This PDF file contains the front matter associated with SPIE Proceedings Volume 9884, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The external control of biologically-active substrates with high spatial and temporal resolutions has already strongly impacted many fields of Biology. This lecture will illustrate how light can be used to control and analyze biological processes.

Nanophotonic systems such as plasmonic and 2-D materials and metamaterials serve as excellent platforms to study and control several optical and chemical phenomena such as spontaneous emission, absorption, Raman scattering and photocatalysis. Techniques such as atomic force microscopy and scanning electron microscopy enable the imaging of nanoscale features, while other techniques such as scanning tunneling microscopy and scanning near-field optical microscopy, enable the near-field optical characterization of nanoscale materials. However, most of these techniques do not allow for simultaneous imaging of topographical features and spectroscopic characterization with high spectral selectivity and temporal resolution. Here, we make use a new imaging technique called photo-induced force microscopy [1,2], which enables imaging and optical characterization of nanoscale materials with very high spatial and temporal resolution. In this technique, a nanoscale tip is brought in the vicinity of the sample, which is optically excited. The photo-induced gradient forces between the tip and the sample can be detected with nanometer-scale spatial resolution, along with topographical information, akin to an atomic force microscope. The photo-induced gradient forces, which are very sensitive to polarization and the distance of the tip from the sample, can be read out and converted to electric fields [2]. As a proof-of-concept demonstration, we image the transverse and longitudinal resonances in gold nanorods and compare their field enhancements to gap plasmons of gold dimers. [1] J. Jahng et al. Gradient and scattering forces in photo-induced force microscopy. Phys. Rev. B 90, 155417 (2014). [2] F. Huang et. al., Imaging nanoscale electromagnetic near-field distributions using optical forces, Sci. Rep. 5, 10610 (2015).

Often, in bio-sensing applications rely on fluorescence as the transduction mechanism. The emission from the fluorescently labeled molecules is detected and quantified to obtain the concentration. Most current techniques, such as ELISA, FISH, next generation DNA sequencing and others need one or several washing steps to remove the unreacted fluorescent molecules to reduce the background noise. To address that problem, we propose an integrated nano-photonic solution for on-chip fluorescence detection. The proposed platform is tailored for bio-sensing applications and has the potential to analyze bio-molecular interactions down to the single molecule level. The technology is based on near-field excitation and collection using PECVD Silicon Nitride (SiN) nano-photonic rib waveguides. SiN provides the combination of high-index-contrast and compatibility with CMOS processing technology, and unlike silicon, Silicon Nitride does not absorb in the visible wavelength window. The evanescent tail of the used SiN waveguide mode extends from 80 nm to 200 nm above the waveguide surface depending on the waveguide geometry, cladding material and excitation wavelength. Hereby, the evanescent field of the waveguide mode excites a very thin layer of molecules near to the surface. The subsequent emission from the excited fluorophore is collected in the near field by coupling to another waveguide. The coupling strength mainly depends on the distance between the waveguide and fluorophore. This way, both the excitation and collection efficiency have an exponential dependency on the distance between the molecule and waveguide surface. Therefore, exciting and collecting fluorescence using photonic waveguides improves the separation between the surface bound fluorescence signal from the bulk background noise, paving the way for wash free bio-sensing. Wash-free assays allow to examine the bio-molecular interactions in real time and simplify the sample/liquid handling system. Next to bulk fluorescence, autofluorescence generated in the SiN waveguide is another large contributor to noise. In the proposed design, the two separate single mode waveguides we use to excite fluorophores and collect the emission, are placed orthogonally in a cross configuration. The orthogonal placement of two Transverse Electric (TE) mode waveguides makes sure that the auto-fluorescence generated in the excitation waveguide is not coupled to the emission waveguide. As a result, we observe an improved signal-to-noise-ratio (SNR) which is a very critical parameter towards single molecule detection. In this talk, I will talk about the design, fabrication and characterization of the proposed cross-configured waveguide based fluorescence detection platform. Experimental results to quantify the excitation efficiency, collection efficiency and SNR will be discussed. A comparison will be shown between the Finite Difference Time Domain (FDTD) simulation and experimental results.

Resonance energy transfer (RET), both radiative and nonradiative, is a well-known process in the molecular fluorescence field. On the other hand, RET has been much less explored in connection with phosphorescent systems. We have recently studied in detail phosphorescence reabsorption (radiative transfer) of polycyclic aromatic hydrocarbons in the presence of excited-state absorption. In this case, reabsorption of phosphorescence results from triplet-triplet (T-T) absorption overlapping the emission spectrum, i.e. Tn ← T1 radiative transitions, and not from absorption by ground state molecules, owing to the forbidden nature of the Tn←S0 radiative transitions. In this way, all absorbing molecules are already in the T1 state, and are generated in the first place by the external source, whose intensity and spatial distribution completely determines the set of allowed sites for excitation diffusion. The excitation moves from one triplet, that returns to the ground state, to another, that undergoes the fast sequence T1→Tn→T1 and thus remains unchanged, hence the elementary process for radiative transfer is T1 + T1 → S0 + T1. The process may take place a number of times. In this mechanism there is no radiation imprisonment, only a peculiar type of inner filter effect, as the emitted photon is lost and does not reach the detector. Unlike the fluorescence reabsorption process, phosphorescence reabsorption depends significantly on the excitation intensity, which determines the number and spatial distribution of triplets. Furthermore, the reabsorption probability is time-dependent, as the T-T absorption contribution to the optical thickness of the medium continuously decreases with time, after excitation cut-off: For sufficiently long times, the phosphorescence absorption probability is negligible, and the decay becomes exponential. However, for shorter times the decay has a distinctive form, displaying an initial concavity when reabsorption is significant [3,4]. For sufficiently high concentrations (typically around 0.01 M), nonradiative transfer of the type T1 + T1 → S0 + Tn (the final triplet state after relaxation being T1) by the dipole-dipole mechanism can also occur. Here, the phosphorescence decay is affected owing to an increase of the nonradiative decay rate. This process is sometimes called long-range triplet-triplet annihilation. For even higher concentrations (typically around 0.1 M) a significant fraction of molecules is so close that the exchange interaction is now operative. In this way, for high excitation intensities short-range triplet-triplet annihilation, T1 + T1 → S0 + S1, eventually preceded by triplet energy migration, T1 + S0 → S0 + T1, comes into play. The phosphorescence decay is again affected and delayed fluorescence may be observed. In this work, we discuss radiative and nonradiative transfer of energy owing to triplet-triplet absorption, including the effect of dimensionality. [1] D. L. Andrews and A. A. Demidov eds., Resonance Energy Transfer, Wiley, Chichester, 1999. [2] B. Valeur and M. N. Berberan-Santos, Molecular Fluorescence. Principles and Applications, Wiley-VCH, Weinheim, 2nd ed., 2012. [3] T. Palmeira, M. N. Berberan-Santos, J. Lumin. 158 (2015) 510-518. [4] T. Palmeira, A. Fedorov, M. N. Berberan-Santos, ChemPhysChem 16 (2015) 640-648.

In this work, an electromagnetic energy harvester operating at microwave frequencies is designed based on a cut- wire metasurface. This metamaterial is known to contain a quasistatic electric dipole resonator leading to a strong resonant electric response when illuminated by electromagnetic fields.1 Starting from an equivalent electrical circuit, we analytically design the parameters of the system to tune the resonance frequency of the harvester at the desired frequency band. Subsequently, we compare these results with numerical simulations, which have been obtained using finite elements numerical simulations. Finally, we optimize the design by investigating the best arrangement for energy harvesting by coupling in parallel and in series many single layers of cut-wire metasurfaces. We also discuss the implementation of different geometries and sizes of the cut-wire metasurface for achieving different center frequencies and bandwidths.

Sub-wavelength Fabry-Perot like resonators are studied both in reflection and transmission for the purpose of second order frequency conversion. The latter are able to hugely confine incoming electric field at resonance inducing great quantity of non linear polarization and thus resonant Sum or Difference Frequency Generation. A metamaterial model is used to homogenize the structure composed of an alternation of non linear dielectric crystal and of metal to predict its resonance wavelengths. The subsequent effective non linear susceptibility for the homogenized layer is driven by the nonlinearities of the dielectric material and by the geometrical parameters, thus leading to much higher susceptibility than existing materials. Besides, the obtained frequency spectra offer a great visibility on the various mode matching scenarios that allow to reach enhanced non linear efficiency highly depending on whether the produced wave is back- or forward propagating.

Nanolasers have steadily gained interest in the past years thanks to considerable technological advances. Interest in very small lasers dates back to the early 1980’s and considerable effort was placed throughout the 1990’s on understanding the threshold and coherence properties of the so-called thresholdless laser. Little progress has been made on this front, mostly due to the scant amount of information coming from experiments, limited by the current detection technology. Very small-sized lasers, thanks to their extremely reduced cavity (and active medium) volumes, offer very low thresholds, but also an accompanying exiguous photon flux, which renders detection extremely challenging. Coupled to very fast internal constants, this requirement renders most kinds of measurements currently impossible: only statistical information, based on photon counting, has been gathered from nanolasers. The problem is aggravated from a fundamental understanding viewpoint, by the fact that most of these devices are optically pumped – i.e., they suffer from poor stability and reproducibility in operating parameters – and emit very short light pulses. This paper gives a brief overview of these problems and discusses the potential for using somewhat larger devices (mesolasers), for which full detection capabilities (barely) exist. As shown with the help of a new modeling approach compared to experimental results, lasers in the mesoscale display emerging properties which can be expected to exist in nanolasers, but are unknown at the macroscopic scale.

Plasmonic waveguides, which support surface plasmon polaritons (SPP) propagating along metal-dielectric interfaces, offer strong field confinement and are ideal for the design of integrated nano-scale photonic devices. However, due to free-carrier absorption in the metal, the enhanced mode confinement inevitably entails an increase in the waveguide loss. This lowers the device figure-of-merit achievable with passive plasmonic components and in turn hinders the performance of active plasmonic components such as optical modulators.

Nanophotonic structures with narrow optical resonances, such as high-quality factor photonic crystal cavities, in principle enable spectral sensing with high resolution. This can also result in high-sensitivity displacement and/or acceleration sensing if a part of the cavity is compliant. However, the control of the resonance and its optical read-out are complex and usually not integrated with the sensing part. In this talk we will introduce a novel nano-opto-electromechanical system (NOEMS), where actuation, sensing and read-out are integrated in the same device. It consists of a double-membrane photonic crystal cavity, where the resonant wavelength is tuned by electrostatically controlling the separation between the membranes. The output current signal provides direct information about either the wavelength of the incident light or the cavity resonance. This nanophotonic sensing system can be employed to measure the spectrum of incident light, to determine the wavelength of a laser line with pm-range resolution, or equivalently to measure tiny displacements.

Plasmonics has long been seen as a promising technology for integrated optical devices for many fundamental applications such as telecommunications, chemistry, quantum science, and medicine. However, for these devices to be realized in a large scale, they should be CMOS-compatible – a problem for plasmonic devices which have generally relied on noble metals. Recently, CMOS compatible materials titanium nitride and transparent conducting oxides (such as doped zinc oxide) have been proposed as the most promising materials for telecommunication applications. TiN is a gold-like ceramic material with a permittivity cross-over near 500 nm. In addition, TiN can attain ultra-thin, ultra-smooth epitaxial films on substrates such as c-sapphire, MgO, and silicon. Partnering TiN with CMOS-compatible silicon nitride enables a fully solid state waveguide which is able to achieve a propagation length greater than 1 cm for a ~8 μm mode size at 1.55 μm. In fact, similar designs using TiN have outperformed gold waveguides due in large part to the reduced scattering loss of epitaxial quality films. Utilizing highly doped zinc oxide films as a dynamic photonic material, high performance modulators can also be realized. Together, these alternative materials form the base of a fully integrated nanophotonic system, capable of exceptional performance with speeds greater than 1 THz, in large part due to the development of alternative materials. Consequently, nanophotonic technologies are reaching a critical point where many applications including telecom, medicine, and quantum science can see practical systems which provide new functionalities.

Surface plasmon-polariton (SPP) modes supported by various dielectric-metal waveguide configurations facilitate strong enhancement and (subwavelength) confinement of electromagnetic fields, enabling miniaturization of SPP-based nanophotonic components and circuits [1], while also strongly enhancing interaction of quantum emitters (QEs) with SPP guided modes [2]. The latter feature has important implications in quantum optics, sensing and lab-on-a-chip applications. One of the main challenges in developing future nano-scale quantum photonic circuits is to manage combining on a single chip a single-photon source, waveguides, modulators and detectors. In this talk, I discuss the motivation for developing quantum SPP-based components despite inherent propagation losses associated with light absorption by metals and review our latest theoretical and experimental results concerning QE coupling to the SPP modes supported by V-grooves cut in gold, i.e., to channel plasmon polaritons (CPPs) [3]. The results of careful theoretical simulations that enabled us to determine the QE position and orientation for the optimum QE-CPP coupling are presented. Furthermore, the deterministic positioning of a single QE (created by a nitrogen vacancy embedded in a diamond nanoparticle) is described, resulting in the experimental demonstration of efficient (> 40%) coupling to the CPP mode. It is argued that this approach can enable realistic and functional single-photon based plasmonic circuitry and therefore, paves the way towards the development of efficient and long distance transfer of energy in integrated solid-state quantum systems. References: 1. D. K. Gramotnev and S. I. Bozhevolnyi, Nat. Photon. 4, 83 (2010). 2. M. S. Tame et al., Nat. Phys. 9, 329 (2013). 3. E. Bermúdez-Ureña et al., Nat. Commun. 6, 7883 (2015).

We develop a systematic method for deriving a quantum optical multi-mode Hamiltonian for the interaction of photons and phonons in nanophotonic dielectric materials by applying perturbation theory to the electromagnetic Hamiltonian. The Hamiltonian covers radiation pressure and electrostrictive interactions on equal footing. As a paradigmatic example, we apply our method to a cylindrical nanoscale waveguide. We use the resulting multi-mode Hamiltonian to derive an effective phonon-mediated interaction between photons propagating in the material. We predict strong non-linear phase shifts even among two photons, comparable to what can be achieved in nonlinear atomic media (comprising cold Rydberg atoms).

The influence of ripple waves on the band diagram of zigzag strained graphene nanoribbons (GNRs) is analyzed by utilizing the finite element method. Such waves have their origin in electromechanical effects. With a novel model, we demonstrate that electron-hole band diagrams of GNRs are highly influenced (i.e. level crossing of the bands are possible) by two combined effects: pseudo-magnetic fields originating from electroelasticity theory and external magnetic fields. In particular, we show that the level crossing point can be observed at large external magnetic fields (B ≈ 100T ) in strained GNRs, when the externally applied tensile edge stress is on the order of -100 eV/nm and the amplitude of the out-of-plane ripple waves is on the order of 1nm.

We present a full study of an improved nonlinear plasmonic slot waveguides (NPSWs) in which buffer linear dielectric layers are added between the Kerr type nonlinear dielectric core and the two semi-infinite metal regions. Our approach computes the stationary solutions using the fixed power algorithm, in which for a given structure the wave power is an input parameter and the outputs are the propagation constant and the corresponding field components. For TM polarized waves, the inclusion of these supplementary layers have two consequences. First, they reduced the overall losses. Secondly, they modify the types of solutions that propagate in the NPSWs adding new profiles enlarging the possibilities offered by these nonlinear waveguides. In addition to the symmetric linear plasmonic profile obtained in the simple plasmonic structure with linear core such that its effective index is above the linear core refractive index, we obtained a new field profile which is more localized in the core with an effective index below the core linear refractive index. In the nonlinear case, if the effective index of the symmetric linear mode is above the core linear refractive index, the mode field profiles now exhibit a spatial transition from a plasmonic type profile to a solitonic type one. Our structure also provides longer propagation length due to the decrease of the losses compared to the simple nonlinear slot waveguide and exhibits, for well-chosen refractive index or thickness of the buffer layer, a spatial transition of its main modes that can be controlled by the power. We provide a full phase diagram of the TM wave operating regimes of these improved NPSWs. The stability of the main TM modes is then demonstrated numerically using the FDTD. We also demonstrate the existence of TE waves for both linear and nonlinear cases (for some configurations) in which the maximum intensity is located in the middle of the waveguide. We indicate the bifurcation of the nonlinear asymmetric TE mode from the symmetric nonlinear one through the Hopf bifurcation. This kind of bifurcation is similar to the ones already obtained in TM case for our improved structure, and also for the simple NPSWs. At high power, above the bifurcation threshold, the fundamental symmetric nonlinear TE mode moves gradually to new nonlinear mode in which the soliton peak displays two peaks in the core. The losses of the TE modes decrease with the power for all the cases. This kind of structures could be fabricated and characterized experimentally due to the realistic parameters chosen to model them.

A new concept of short wavelength infrared (SWIR) to visible upconversion integrated imaging device is proposed, modeled and some initial measured results are presented. The device is a hybrid inorganic-organic device that comprises six nano-metric scale sub-layers grown on n-type GaAs substrates. The first layer is a ~300nm thick PbSe nano-columnar absorber layer grown in (111) orientation to the substrate plan (100), with a diameter of 8- 10nm and therefore exhibit quantum confinement effects parallel to the substrate and bulk properties perpendicular to it. The advantage of this structure is the high oscillator strength and hence absorption to incoming SWIR photons while maintaining the high bulk mobility of photo-excited charges along the columns. The top of the PbSe absorber layer is coated with 20nm thick metal layer that serves as a dual sided mirror, as well as a potentially surface plasmon enhanced absorption in the PbSe nano-columns layer. The photo-excited charges (holes and electrons in opposite directions) are drifted under an external applied field to the OLED section (that is composed of a hole transport layer, an emission layer and an electron transport layer) where they recombine with injected electron from the transparent cathode and emit visible light through this cathode. Due to the high absorption and enhanced transport properties this architecture has the potential of high quantum efficiency, low cost and easy implementation in any optical system. As a bench-mark, alternative concept where InGaAs/InP heterojunction couple to liquid crystal optical spatial light modulator (OSLM) structure was built that shows a full upconversion to visible of 1550nm laser light.

The optical properties of metal nanostructures result from their localized surface plasmon resonances (LSPRs). The exact spectral positions of LSPRs depend on the geometry of the particles and optical parameters of the surrounding material. In addition, when the nanoparticles are arranged in an array (metasurface) the LSPRs associated with isolated particles are affected by the presence of other array members. As a result, sharp spectral features related to surface lattice resonances (SLRs) can be observed. SLRs are sensitive to the angle of incidence of incoming light due to their association with the appearance and disappearance of diffraction orders in the optical response. The resonances lead to strong local fields (hot spots) in the proximity of the particles. Such hot spots are particularly important when one wants to enhance nonlinear optical effects, for example second-harmonic generation (SHG). In the case of SHG, the sample needs to be also non-centrosymmetric, which can be fulfilled by using, e.g., V-shaped nanoparticles. In this paper, we show that SHG from arrays of V-shaped gold nanoparticles can be enhanced when the angle of incidence is matching optimal conditions for the excitation of SLRs. Our sample consists of an array of V-shaped nanoparticles fabricated by standard electron-beam lithography and lift-off techniques. The gold particles are distributed in the array with a spacing of 500 nm and have the same dimensions to obtain a resonance close to fundamental wavelength for the polarization along the symmetry axis. The SHG experiments were performed in transmission mode with the incident beam weakly focused on the samples. Polarizers and a half-wave plate were used to control the polarizations of the fundamental and second-harmonic beams. The SHG signal was collected by a photon-counting system for varying incident angles (rotation with respect to the symmetry axis (y) of the sample or orthogonal to it (x)). SLRs can modify LSPRs leading to visible features in the SHG response. When the incident angle is increased, a redshift towards fundamental wavelength is observed together with narrowing of the resonance. Such improvement in the quality of the resonance results in stronger SHG. Thus, the sample needs to be rotated significantly to meet the optimal conditions for SHG enhancement, which can be as high as by a factor of four (projection x-z) or a factor of 10 (projection y-z) comparing to SHG measured at normal incidence. The maximum enhancement of the SHG signal is related to the SLRs which occur near incident angles that allow diffraction orders to propagate along the sample plane (in air or in the substrate). Our investigation of the role of SLRs in SHG from metasurfaces shows that such resonances lead to prominent features in the angle-dependent SHG responses, which results in the enhancement of SHG by a factor of up to ten. In order to achieve the optimal conditions of SHG enhancement the sample needs to be rotated from normal incidence to match the angle that allows diffraction order to propagate in the substrate.

Raman scattering is most commonly associated with a change in vibrational state within one molecule, with signals in the corresponding spectrum widely used to identify material structures. When the corresponding theory is developed using quantum electrodynamics, the fundamental scattering process is described by a single photon of one radiation mode being annihilated with the concurrent creation of another photon; the two photon energies differ by an amount corresponding to the transfer of vibrational energy within the system. Here, we consider nanoscale interactions between neighboring molecules to mediate the process, by way of a virtual photon exchange to connect the evolution of the two molecular states. We consider both a single and pair of virtual photon exchanges. Our analysis deploys two realistic assumptions: in each pairwise interaction the two components are considered to be (i) chemically different and (ii) held in a fixed orientation with respect to each other, displaced by an amount equivalent to the near-field region; resulting in higher order dependences on displacement R becoming increasingly significant, and at the limit the short-range R-6 term can even dominate over R-3 dependence. In our investigation one center undergoes a change in vibrational energy; each neighboring molecule returns to the electronic and vibrational state in which it began. For the purposes of providing results, a Stokes transition has been assumed; analogous principles hold for the anti-Stokes counterpart. Experimentally, there is no change to the dependence on the intensity of laser light. However, the various mechanisms presented herein lead to different selection rules applying in each instance. In some cases specifically identifiable mechanisms will be active for a given transition, leading to new and characteristic lines in the Raman spectrum. A thorough investigation of all physically achievable mechanisms will be detailed in this work.

We present theoretical studies of elementary exciton and charge transfer processes in functional organic materials, in view of understanding the key microscopic factors that lead to efficient charge generation in photovoltaics applications. As highlighted by recent experiments, these processes can be guided by quantum coherence, despite the presence of static and dynamic disorder. Our approach combines first-principles parametrized Hamiltonians, based on Time-Dependent Density Functional Theory (TDDFT) and/or high-level electronic structure calculations, with accurate quantum dynamics simulations using the Multi-Configuration Time-Dependent Hartree (MCTDH) method. This contribution specifically addresses charge generation in a novel class of highly ordered oligothiophene-perylene diimide type co-oligomer assemblies, highlighting that chemical design of donor/acceptor combinations needs to be combined with a detailed understanding of the effects of molecular packing.

Plasmon-enhanced nonradiative energy transfer is demonstrated in two inorganic semiconductor systems. The first is comprised of colloidal nanocrystal CdTe donor and acceptor quantum dots, while the second is a hybrid InGaN quantum well-CdSe/ZnS quantum dot donor-acceptor system. Both structures are in a planar geometry. In the first case a monolayer of Au nanospheres is sandwiched between donor and acceptor quantum dot monolayers. The largest energy transfer efficiency is seen when the donor is ~3 nm from the Au nanopshere. A plasmon-enhanced energy transfer efficiency of ~ 40% has been achieved for a separation of 3 nm between the Au nanopshere monolayer and the acceptor monolayer. Despite the increased energy transfer efficiency these conditions result in strong quenching of the acceptor QD emission. By tuning the Au nanosphere concentration and Au nanosphere-acceptor QD separation the acceptor QD emission can be increased by a factor of ~2.8. The plasmon-enhanced nonradiative energy transfer is observed to extend over larger distances than conventional Forster resonance energy transfer. Under the experimental conditions reported herein, it can be described by the same d-4 dependence but with a larger characteristic distance. Using a Ag nanobox array plasmonic component plasmon-enhanced nonradiative energy transfer has also demonstrated from an InGaN quantum well to a ~80 nm thick layer of CdSe/ZnS colloidal quantum dots. An efficiency of ~27% is achieved, with an overall increase in the QD emission by ~70%.

Besides inorganic semiconducting and dielectric nanowires, the study of pi-conjugated and hybrid 1D-nanostructures is a fastly growing domain of research because of the great versatility offered by their architectures at the scale of the characteristic physical lengths. Novel nano-architectures give opportunities to control the optoelectronic properties, that could result in new paradigms for devices, such as nano-sources for tagging, sensing and lasing. Moreover, the 1D geometry promotes sub-wavelength optical propagation and cavity effects suitable for integrated nanophotonic devices (for a review, see [1]). Here, the color control in coaxial hybrid nanowires and the visible light propagation in polymeric nanotubes are reported, as well as nanosources combined within a single nanowire waveguide. In the first study, we propose an alternative strategy to get bright nano-emitters whose spectral emission can be precisely and simply anticipated. It consists in minimizing the role of charge and energy transfer mechanisms between the two species, in contrast to the common donor-acceptor strategy. In a practical way, the first key point is the selection of two luminophores with no overlapping in their absorption and emission spectral range. The second key point is the spatial separation of the two types of luminophores in a coaxial geometry to prevent charge and energy transfer. [2] For nanowires fabricated by a template strategy, this was achieved by first depositing nanotubes of a pi-conjugated green polymer with a solvent-assisted method. Then, the nanotubes were filled with a PMMA-red emitter composite. It has been shown that this strategy promotes a simple and fine tuning of the photoluminescence features with both species in similar concentration. These advantages could make our strategy a new paradigm for nano-emitters. In the second study, the propagation of light in the visible range along polymeric nanotubes has been investigated. The case of nanotubes is of particular interest because only few studies are reported in the literature and it permits higher interactions between the propagating light and both the surrounding medium and the inner channel, highly suited for nanosensors. The light was directly injected within nanotubes of SU-8 photoresist (a standard in integrated microdevices). The attenuation coefficient estimated by a cut-back like method has typical values of about 10 dB/cm. Simulation by FDTD has shown that most of the losses are due to leakages through the SiO2 substrate. [3] Thus, such polymeric nanowires and nanotubes are very competitive structures as sub-wavelength waveguides. Recent developments focused on combining fluorescent conjugated molecules within passive polymeric nanotubes will also be reported. [1] A. Garreau, J.L. Duvail Advanced Optical Materials 2, 1122-1140 (2014) [2] A. Garreau et al., ACS Nano 7, 2977–2987 (2013) [3] J. Bigeon, N. Huby, J.L. Duvail, B. Bêche, Nanoscale 6, 5309 (2014)

Optical antennas have the prospect to redirect light rays into engineered directions at the subwavelength scale. They offer new options for photodetection, color routing, fluorescence emission and sensing applications. Previously, metallic nanoantennas based on localized surface plasmon resonance (LSPR) have commonly been exploited to fulfill this purpose, e.g. the gold Yagi-Uda array and split-ring resonator. However, the intrinsic ohmic losses of metals are large especially in the visible range, hindering further efficiency improvement for practical applications. In addition, the interaction of the metallic nanoantennas with the magnetic component of light is relatively weak, adding to their lack of highly tunable scattering directionality. In this presentation, we will demonstrate our recent experimental progress on all-dielectric nanoantennas made of amorphous silicon with tunable scattering directionality. Our nanoantennas are designed as V-shaped single element and fabricated using electron-beam lithography followed by dry reactive ion etching. It is illustrated that the scattering cross section of the silicon nanoantenna can be considerably higher than that of comparable Au antennas. In addition, the extinction coefficient of amorphous silicon is adequately low in the considered wavelength range, resulting in minimal absorption losses and an enhanced scattering efficiency. More interestingly, compared to Au nanoantennas that exhibit light scattering in a single particular direction, by carefully engineering the geometry of the silicon nano-antennas, their scattering can be effectively tuned into two opposite directions within the visible range (Supporting figure). Over a spectral range of less than 100 nm, the scattering directionality gradually shifts from the leftward to the rightward. More simulation results based on the finite difference time domain (FDTD) methods are available to perfectly match and corroborate our experimental measurement. Initial analysis of the underlying physics for the tunable scattering directionality will also be discussed. Such unique optical properties make the silicon nanoantenna promising candidates for novel low-loss optical devices that can enable unprecedented control over the scattering directionality.

We present an optical slot antenna integrated with a metal-dielectric-metal (MIM) plasmonic waveguide. By integrating optical slot antenna on top metal layer of MIM waveguide, we can couple the plasmon guide mode into the feed antenna directly. The resonantly excited slot antenna works as a magnetic dipole and then radiates in dipole-like far-field pattern. By adding an auxiliary groove structure along with the slot antenna, the radiation can be directed into the direction where the structure determined. The demonstrated optical slot antenna integrated with a plasmonic waveguide can be used as a “plasmonic via” in plasmonic nanocircuits.

Scanning Near-field Optical Microscopy (SNOM) is an essential tool in nano-optics and plasmonics. Among many variants of SNOM, a plasmonic tip is a new type of SNOM tip that is based on a resonant excitation and a superfocusing of a radially polarized conical surface plasmon polariton (SPP). The plasmonic tip is made of a tapered and fully metal-coated M-profiler fiber tips. An M-profile fiber guides the radially polarized fiber mode securely to the tapered region of the tip where it resonantly excites the radially polarized plasmon mode. This resonant excitation process allows us to have higher energy conversion efficiency that is up to 70% for 50 nm gold coating thickness from far-field to near-field than other SNOM tips like aperture tips (0.01% for 100 nm aperture). As the radially polarized plasmon mode further propagates towards the apex, its’ intensity increases anomalously, and its’ phase velocity decreases. Thus, the plasmon gets localized longitudinally as well as transversally due to the SPP nature. This phenomenon is known as a superfocusing of SPP, and in conical structure, it happens only for the fundamental radially polarized mode in the region where the tip radius is smaller than 50 nm. In this study, we introduce the plasmonic tip and explore the plasmon excitation process on a planar gold surface by plasmonic tips and circular aperture SNOM tips to understand the tip emission behavior in near-field. In the experiment, we use ring gratings that are milled on a planar gold surface and place a tip at the center of the structure to excite a planar SPP that propagates toward the grating and gets scattered. By imaging the scattered light through the grating, we study the plasmon excitation pattern and deduce the near-field at the apex. An emission through a small metal aperture (~10 nm) is well explained by Bethe theory that states that the near-field emission resembles that of a dipole. However, for an aperture tip with an aperture as large as 100 nm, we demonstrated that the dipole approximation well describes the excited SPP as long as a linearly polarized single mode is guided within the tip. When the aperture gets larger, the guided light within the tip becomes multimode; thus, the dipole approximation is no longer valid although the tip far-field emission looks like a Gaussian mode. For the plasmonic tip, we showed the emission can be approximated that of an out-of-plane dipole (oscillating perpendicular to the surface) despite the size of the apex. This method allows us also estimate the tilt of a tip with respect to the sample surface and purity of guided mode within the tip, and these information are essential for interpreting the detected signal from the sample. In conclusion, we introduce the plasmonic tip as an efficient SNOM tip due to its resonant excitation of SPP and superfocusing processes, and studied the near-field excitation characteristics in comparison with the conventional aperture tips.

Plasmonic nanostructures with strong near field “hot spots” are highly demanded in many applications such as surface enhanced Raman spectroscopy (SERS). Here, we present some specially designed plasmonic hierarchical nanostructures that combine geometric features of micro- and nanoscales. Owing to the mode coupling and hybridization in these multiscale systems that can produce the cascaded field enhancement (CFE) effect, extremely strong and highly confined field hot spots can be readily generated in nanoscale volumes. Two typical hierarchical nanostructures are presented: an Mshaped grating with 30 nm narrow V-shaped grooves and a nanoparticle-in-cavity (PIC) plasmonic nanoantenna array. A cost-effective, efficient and reliable fabrication technique based on room-temperature nanoimprinting and anisotropic reactive ion etching is developed to fabricate these plasmonic hierarchical nanostructures in large area, during which the nano-features can be finely controlled and tuned. The field distributions and enhancement in the proposed structures are experimentally characterized, which agree very well with the numerical simulations. SERS experiments show the SERS enhancement factor as high as 5×10⁸ by employing these hierarchical nanostructures as SERS substrates, which verify the strong light-matter interaction and show the great potential of these devices as low-cost and highly-active substrates for SERS applications.

Confocal fluorescence lifetime imaging microscopy method is used to obtain individual fluorescence intensity and lifetime values of aromatic Perylene dye molecules encapsulated into PMMA based nanofibers. Fluorescence spectrum of aromatic hydrocarbon dye molecules, like perylene, depends on the concentration of dye molecules and these dye molecules display an excimeric emission band besides monomeric emission bands. Due to the dimension of a nanofiber is comparable to the monomer emission wavelength, the presence of nanofibers does not become effective on the decay rates of a single perylene molecule and its lifetime remains unchanged. When the concentration of perylene increases, molecular motion of the perylene molecule is restricted within nanofibers so that excimer emission arises from the partially overlapped conformation. As compared to free excimer emission of perylene, time-resolved experiments show that the fluorescence lifetime of excimer emission of perylene, which is encapsulated into NFs, gets shortened dramatically. Such a decrease in the lifetime is measured to be almost 50 percent, which indicates that the excimer emission of perylene molecules is more sensitive to change in the surrounding environment due to its longer wavelength. Fluorescence lifetime measurements are typically used to confirm the presence of excimers and to construct an excimer formation map of these dye molecules.

The unique optical properties of fluorophores nanoparticles doped with rare earth elements have attracted a lot of attention in the scientific community due to their potential application from biological imaging to quantum information. In this work, we compare the photoluminescence of nanoparticles measured by two different means: traditional objective based microscopy and fiber based optical tweezers. Our doped NaYF4 nanocrystals are prepared through solvothermal synthesis. Ytterbium and erbium codoping provides nanoparticles with luminescence properties. Under IR laser excitation, the nanoparticles present strong and photostable upconversion signals in the visible range. In addition, by changing the gadolinium content of the host matrix, we obtain nanorods with a controlled aspect ratio up to 20 and a well defined crystalline structure. The high anisotropy of the nanoparticles results in a strong polarisation of the photoluminescence. To investigate this property, we observed our nanoparticles using a confocal microscope and studied the dependency of the polarisation with the length of the particles. To complete our characterization, we used optical tweezers to trap nanoparticles in water. We first show the possibility to trap these nanoparticles with an original optical tweezers based on two chemically etched fibers. Due to the optical forces applied by the laser beam coupled into the fibers, the nanorods align themselves between the two fibers along their long axis. Afterwards, the fibers are not only used to trap the particles but also to collect the luminescence emitted only by the trapped nanoparticles. By this mean, we can analyse the emitted light with a spatial resolution. This result will be compare to previous observation done on the same particles with our confocal microscope. Moreover, an orthogonal third fiber was implemented in the set up. This fiber can move along the particle and collect the light emitted at different point. We present the link between the photoluminescence properties and the emission point by moving this last fiber. In addition, our optical tweezers are associated to a traditional objective-based optical microscope. We compared the photoluminescence emitted by particles in a homogeneous medium (water) or at an interface when drop casted on a coverslip.

Hyperbolic plasmonic metamaterials provide numerous opportunities for designing unusual linear and nonlinear optical properties. Here we report a full vectorial numerical model to study SHG in a plasmonic nanorod metamaterial slab. Our frequency-domain implementation of the hydrodynamic model of the metal permittivity for conduction electrons provided a full description of the nonlinear susceptibility in a broad spectral range. We show that the modal overlap of fundamental and second-harmonic light in the plasmonic metamaterial slab results in the frequency tuneable enhancement of radiated second-harmonic intensity by up to 2 orders of magnitudes for TM- and TE-polarized fundamental light, compared to a smooth Au film under TM-polarised illumination. A double-resonant condition with both the enhancement of fundamental field and the enhanced scattering of the second-harmonic field can be realised at multiple frequencies due to the mode structure of the metamaterial slab. The nanostructured geometry of the Au nanorod metamaterial provides a larger surface area compared to the centrosymmetric crystal lattice of gold, which is needed for exploiting the intrinsic surface nonlinearity of gold. The numerical model allows us to explain experimental investigations on the spectral behaviour and radiation diagram of the second harmonic signal. In the experiments SHG generated under femtosecond excitation with varying wavelength, polarization, and angle of incidence, was characterized in backward and forward directions. We show that the excitation of plasmonic modes in the array can remarkably enhance the nonlinear response of the system, as predicted by the model. The results open up wide ranging possibilities to design tuneable frequency-doubling metamaterial with the goal to overcome limitations associated with classical phase matching conditions in thick nonlinear crystals.

A photovoltaic technology that is not limited to the Shockley–Queisser efficiency limit and that is amenable to low-cost and large-area production requirements is studied in our team. The principle is based on the optical rectification of sunlight. Quarter-wave antennas allow the conversion of optical waves into a potential that is maximum at the tip of the antennas. We use molecules to rectify the potential. We study the rectification at the top of our antennas using the formalism and instrumentation of nonlinear optics. We monitor simultaneously the optical rectification and harmonic generation effects. Careful analysis of the tensorial response of the process allows studying the nature of the rectification happening in various types of nano-structured diodes. The enhancement of the nonlinearity related to the nonlinear process is discussed. It reveals the key ingredients needed to achieve efficient conversion of sunlight into electricity using optical rectification.

I will report on our recent progress in the development of laser printing technologies for fabrication of complex metallic and dielectric nanoparticle structures. Fabrication, characterization, and applications of the generated nanoparticle arrays in nanophotonics, plasmonics, and optical sensing will be demonstrated and discussed.

The emergence of photonic metasurfaces has enabled a new paradigm of light control through the introduction of surface discontinuities. Space-gradient metasurfaces consist of planar arrays of nano-structured antennas which induce spatially varying phase and/or polarization to propagating light. As a consequence, photons propagating through space-gradient metasurfaces can be engineered to undergo a change to their momentum, angular momentum and/or spin state. This has led to a relaxation of Snell’s law, a pivotal relation in optical engineering, and has enabled a whole new family of flat optical devices. We have utilized the engineered control over photonic spin and momentum to develop a set of ultra-compact metasurface based devices including a chiroptical spectrometer that can be used for biochemical sensing, a polarization rotator with possible applications for secure quantum communication, and nano-cavities to enhance photonic spontaneous emission using the Purcell effect. It has been recently demonstrated that the field of flat photonics is further empowered by utilizing time-gradient metasurfaces with dynamic responses to propagating light. A new genus of optical devices and physical effects can be realized provided one can overcome some fundamental limitations of metasurfaces with space-gradient alone. Photons experience inelastic interactions with time-varying metasurfaces resulting in a Doppler-like wavelength shift. Furthermore, Snell’s relations are modified to a more universal form not limited by Lorentz reciprocity, hence meeting all the requirements to build magnetic-free optical isolators. Consequently, metasurfaces with both space- and time-gradients can have a strong impact on a plethora of photonic applications and provide versatile control over the physical properties of light.

The control of the Förster resonance energy transfer (FRET) rate between molecules has recently received a lot of interest, opening opportunities in the development of sources of incoherent illumination, photovoltaics and biosensing applications. The design of nanostructured materials with appropriate electromagnetic properties, particularly with the engineered local density of electromagnetic states (LDOS), allows the enhancement of the spontaneous emission rate of emitters in their vicinity. However, the question of the influence of the LDOS on the energy transfer rate between emitters remains controversial. To date, several contradicting theoretical and experimental studies involving emitters on metallic surfaces and plasmonic metamaterials as well as in optical cavities and plasmonic antennas have been reported. In this work we study the influence of the LDOS on the energy transfer between donor-acceptor pairs placed inside the anisotropic metamaterial. The study of the emission kinetics of both the donor and the acceptor allow us to experimentally compare FRET efficiencies in different electromagnetic environments including dielectric and plasmonic substrates as well as metamaterials.

Plasmonics in the UV-range constitutes a new challenge due to the increasing demand to detect, identify and destroy biological toxins, enhance biological imaging, and characterize semiconductor devices at the nanometer scale. Silver and aluminum have an efficient plasmonic performance in the near UV region, but oxidation reduces its performance in this range. Recent studies point out rhodium as one of the most promising metals for this purpose: it has a good plasmonic response in the UV and, as gold in the visible, it presents a low tendency to oxidation. Moreover, its easy fabrication through chemical means and its potential for photocatalytic applications, makes this material very attractive for building plasmonic tools in the UV. In this work, we will show an overview of our recent collaborative research with rhodium nanocubes (NC) for Plasmonics in the UV.

Two-photon polymerization, optionally combined with stimulated emission depletion (STED) lithography, allows two and three dimensional polymer fabrication with structure sizes and resolution below the diffraction limit. Structuring of polymers with photons, whose wavelength is within the visible range of the electromagnetic spectrum, gives new opportunities to a large field of applications e.g. in the field of biotechnology and tissue engineering [1]. Radical photoinitiator molecules (fluorophores) in an acrylic negative tone photoresist are excited with a near infrared laser via two photon absorption; this allows writing of features as small as ~100 nm. To achieve spatial polymerization restriction similar to STED-microscopy [2, 3], the excited photoinitiators are depleted in the outer rim of the excitation volume via stimulated emission by a second laser beam. An appropriate beam shaping shrinks the volume of excited photoinitiators. Thereby, polymerization initiation is furtherly confined. The feature size can be decreased to several tens of nanometers in any desired geometry using stimulated emission depletion (STED) [2-5]. Currently, feature sizes as small as 55 nm and a lateral resolution of 120 nm of adjacent lines can be achieved [5, 6]. Feature size as well as structure resolution are mainly limited by the used photoresists. Future applications of sub-diffraction optical lithography include optical data storage and nanophotonic devices. Recently, STED lithography allows us to produce well characterized, biocompatible nanoanchors as platforms for single, biochemically active proteins, applicable to many biological assays [6, 7]. 1. Maruo, S., O. Nakamura, and S. Kawata, Three-dimensional microfabrication with two-photon-absorbed photopolymerization. Opt Lett, 1997. 22(2): p. 132-4. 2. Klar, T.A. and S.W. Hell, Subdiffraction resolution in far-field fluorescence microscopy. Opt Lett, 1999. 24(14): p. 954-6. 3. Klar, T.A., et al., Fluorescence microscopy with diffraction resolution barrier broken by stimulated emission. Proc Natl Acad Sci U S A, 2000. 97(15): p. 8206-10. 4. Fischer, J., G. von Freymann, and M. Wegener, The Materials Challenge in Diffraction-Unlimited Direct-Laser-Writing Optical Lithography. Advanced Materials, 2010. 22(32): p. 3578-+. 5. Wollhofen, R., et al., 120 nm resolution and 55 nm structure size in STED-lithography. Opt Express, 2013. 21(9): p. 10831-40. 6. Klar, T.A., R. Wollhofen, and J. Jacak, Sub-Abbe resolution: from STED microscopy to STED lithography. Physica Scripta, 2014. 162: p.14049 7. Wolfesberger, C., et al., Streptavidin functionalized polymer nanodots fabricated by visible light lithography. J Nanobiotechnology, 2015. 13(1): p. 27.

Measuring the state of polarization (SoP) of light beams is of paramount importance in many scientific and technological disciplines, including chemistry, biosensing, astronomy and optical communications. Commercial polarimeters are built by using bulky and expensive optical elements, including half-wave plates or grid polarizers, with little prospect for miniaturization. Inspired by the concept of spin-orbit coupling, here we introduce a nanophotonic polarimeter that measures the full SoP – Stokes parameters – of a light beam over an ultrabroad wavelength range. The active region of the device, formed by a metallic nanoantenna on top of a silicon waveguide crossing, is less than a square wavelength, one order of magnitude smaller than polarimeters based on metasurfaces and many orders of magnitude smaller than commercial devices. Our approach is universal and therefore applicable to any wavelength regime and technological platform, opening a new route for miniaturized polarimeters.

The technique of the laser controlled deposition of sodium and rubidium deposits on the sapphire substrate is presented. The metals were deposited on the clean sapphire substrate from the vapor phase contained in the evacuated and sealed cell. We use an axicon to produce a non-diffracting Bessel beam out of the beam got from the cw diode laser with 200 mW power at the wavelength of 532 nm. After 30 minutes of the laser-controlled deposition the substrates were examined in the optical microscope. The obtained metal deposits form the sharp-cut circles with the pitch of 10 μm, coincident with the tens of dark rings of the Bessel beam. Reduction of the laser power leads to the build up of the continuous metal film over the whole substrate.

Nonlinear optical processes are known to be weak in bulk materials and extremely small at the nanoscale since they mainly scale with the volume. Here I will show how we enhance second-harmonic generation in two typical χ2 non centrosymmetric nanomaterials. First, in barium titanate nanoparticles, we take advantage of various resonances occurring in the visible wavelength range. Contrary to plasmonics occurring in metallic nanostructures, those resonances take place in dieletric nanoparticles and they are well described by the Mie scattering theory. Second, in lithium niobate nanowires, we demonstrate phase-matching and use it to increase the guided second-harmonic power by a factor of more than 80. We also increase non-phase-matched guided second-harmonic by engineering the nanowire length. Those bright nanostructures can serve for developing compact efficient nonlinear optical sources or waveguides.

Two-dimensional metamaterials (metasurfaces) have led to many exciting phenomena both in linear and nonlinear optics. In this talk I will present an overview of some recent results for both metallic and dielectric metasurfaces. Record second order nonlinearities can be obtained when metallic metasurfaces are coupled with resonant electronic transitions in semiconductors such as intersubband transitions. Additionally, since the nonlinear unit in this case is a single resonator coupled to the semiconductor heterostructure, additional functionality can be obtained at the second harmonic beam. This phenomena can be described as a phased-array source. Using this principle, we have created beam and polarization splitters operating at the second harmonic wavelength. This is new functionality that has no counterpart in conventional nonlinear optical materials. Another interesting case is the combination of all-dielectric metasurfaces with nonlinear optical phenomena, both bulk and surface enhanced. All-dielectric metasurfaces provide a platform to engineer magnetic and electric resonant modes in wavelength-scale nanoresonators with very low loss. Fabricating such dielectric metasurfaces from different types of semiconductors can be used to enhance their second and third order nonlinearities by several orders of magnitudes.

In recent years, nanotechnology and nanoscience have been expanding their toolbox dramatically. Metallic nanoantennas – also known as plasmonic resonators – can be considered as one of these novel tools providing an effective route to couple photons in and out of nanoscale volumes. The higher the level of control over the way a nanoantenna interacts with light, the more effective this tool becomes and the further its applications will reach. Essential to this end is a detailed knowledge of such an antenna’s scattering characteristics. Especially in nanophotonics applications where every photon counts, one immediately benefits from directed photon routing for efficient photon collection. Recent studies have demonstrated that proper antenna designs can result in scattering patterns strongly deviating from the trivial dipole distribution, allowing one to route light in specific directions. [1–4] For instance, left-to-right directionality or unidirectional side scattering (i.e. preferential scattering in a single direction perpendicular to the incident wave) with only a single nanoparticle geometry, namely a V-antenna, was demonstrated by our group. [3, 4] Nevertheless, selectively steering photons at the nanoscale remains a fundamental challenge and most works are, unfortunately, lacking a clear rigorous analysis of the antenna behavior. This constrains the further development of more complex radiative functionality, such as for instance bi-directional scattering where photons of different energy are routed into opposite directions. Here, first, we elucidate the basic principles underlying directional plasmonic nanoantennas. By applying an eigenmode decomposition of full-field 3D simulations (Method of Moments and Finite Difference Time Domain) we are able to rigorously determine the underlying mode interferences that give rise to the experimentally observed directional behaviour. [4] An important result from this analysis is the conclusion that directional behaviour is strongly dependent on the type of antenna feed that is applied, an effect mostly ignored so far. For instance, plane wave excitation is directed in opposite direction from the radiation of a point dipole source. Next, the obtained design principles are applied to construct a bi-directional metallic nanoantenna with a single feed-gap. This means that, for instance, a mix of quantum emitters can be placed in the antenna gap and that the multi-colored emission can be de-multiplexed by beaming different spectral bands in opposite directions. Both the bi-directional scattering of a plane wave and bi-directional emission of local dipole emitters are experimentally verified by means of back-focal-plane microscopy. We demonstrate directional tunability by varying the antenna structural parameters, allowing further optimisation and spectral control. The obtained insight in how directional emission and scattering are generated and how different modes come together to form far-field properties of a nanoantenna device is indispensable to create new nanoscale optical devices for sub-wavelength color routing and self-referenced directional sensing. Moreover, we believe the same concepts are applicable to dielectric nanoantennas. [1] T. Kosako, et al. Nature Photonics (2010) 4(5), 312–315 [2] T. Shegai, et al. Nat. Comm. (2011) 2(481) [3] D. Vercruysse, et al. Nano Lett. (2013) 13 (8), 3843–3849 [4] D. Vercruysse, et al. ACS Nano (2014) 8(8), 8232−8241

Luminescent lattice defects (so called “color centers”) in diamond provide a robust, solid-state architecture for exploring quantum optics, with many facilitating direct access to highly coherent electron and nuclear spins. The past two decades have seen tremendous advances in our ability to prepare and control the quantum states of these atom-like systems. For instance, demonstrations that leverage the diamond nitrogen vacancy (NV–) center as a spin-photon interface have included the generation of indistinguishable photons, a quantum bit memory exceeding 1 second, entanglement of two distance solid-state qubits, and deterministic long distance quantum teleportation. While diamond color centers are an attractive platform for scalable quantum information processing, the diamond solid-state matrix, by its very nature, inhibits efficient photon collection into either free-space or fiber-optical systems. Due to its large refractive index, emitted photons are inevitably trapped within the diamond crystal by total internal reflection, limiting count rates and overall scalability of information processing via quantum optical protocols. To this end, there has been significant progress towards integrating individual diamond color centers within well-defined radiation channels: namely, those provided by monolithic diamond nanophotonic networks. Currently, on-chip low loss (~ few db/cm) diamond waveguide networks are available, as well as key passive photonic elements like micron scale ring and disk resonators and photonic crystal cavities, with high optical quality (Q) factors. Specifically, we recently demonstrated a scalable ‘angled-etching’ nanofabrication method for realizing nanophotonic networks starting from bulk single-crystal diamond substrates (MJ Burek et al., Nano Letters 2012, MJ Burek et al., Nat Comm. 2014). Angled-etching employs anisotropic oxygen-based plasma etching at an oblique angle to the substrate surface, resulting in suspended optical structures with triangular cross-sections. Using this approach, we demonstrated high Q-factor (> 10^5) optical nanocavities fabricated in bulk single-crystal diamond, operating over a wide wavelength range (visible to telecom). Beyond isolated photonic devices, we have further developed free-standing angled-etched waveguides which efficiently route photons between diamond optical nanocavities, while maintaining physical support through attachment to the bulk substrate. Although on-chip diamond nanophotonics realized by angled-etching continue to mature, efficient off-chip optical coupling schemes which provide near seamless transition of photons on-chip into commercial optical fibers remain an outstanding challenge. This is especially pertinent in applications involving single photons, such as quantum optics with diamond color centers. Herein, we demonstrate a high efficiency fiber-optical interface with aforementioned on-chip diamond nanophotonic networks, achieving > 90% power coupling at both telecom and visible wavelengths. The coupling scheme utilizes a single mode optical fiber, with one end fabricated into a conical taper, to adiabatically transition guided light between on-chip tapered diamond waveguides and off-chip optical fiber networks. Additionally, we develop techniques to robustly pigtail single-mode fibers with diamond waveguide couplers, yielding a packaged technology that may potentially enable deployment in harsh environments, including vacuum, sub-Kelvin cryogenics, or even liquid/biological environments. With these newly developed optical integration schemes, single-crystal diamond is now a viable integrated nanophotonics platform, servicing a range of applications, from non-linear optics and chemical sensing, to quantum science and cavity optomechanics.

Here, we report our investigations on the development of novel, metal-free, organic materials able to harvest triplet states using efficient thermal activated delayed fluorescence (TADF), and dual fluorescence-phosphorescence emissions at room temperature (RT-DFP). These materials show enormous potential in different technological applications, including the development of materials for oxygen,[1] and temperature[2] sensing, optical power limiters,[3] bio-imaging,[4] and in organic light emitting diodes (OLEDs).[5] TADF, also known as E-type delayed fluorescence, has gained very rapid interest as a mechanism to improve efficiencies in OLEDs, due to the possibility of harvesting approx. 100% of the excitons formed from charge recombination, without requiring the use of expensive and scarce materials such as iridium or platinum.[6] As TADF, the observation of RT-DFP in pure organic materials has also potential for many technological applications, and in particular in sensing applications. Recently, organic materials with long lived triplet photo-induced absorption were used to develop optical power limiters for low light levels.[7] Magnetic modulation over visible room temperature phosphorescence using weak magnetic fields was also reported.[8] Moreover, RT-DFP in principle, can be also used as a way to harvest triplet states in OLEDs and produce light directly from both singlet and triplet states, which may allow the design of metal free organic white emitters for lighting applications. In this talk, the complex and rich photophysics of materials showing very efficient TADF and RT-DFP is discussed in detail, showing how a simple change on the molecular structure allows switching-off the strong TADF and opening the channel for efficient RT-DFP to be observed.[9] The role of the energy ordering of electronic states on the efficiency of both mechanisms is also discussed, giving clear guidelines for the design of new emitters, and opening the way for TADF and RT-DFP to be explored in technological applications. References [1] Feng, Y. et al., Analyst, 2012, 137, 4885. [2] Wolfbeis, O.S., Adv. Mater. 2008, 20, 3759. [3] Zhou, G. et al., Adv. Funct. Mater. 2009, 19, 531. [4] Zhang,G. et al,. Nat. Mater. 2009, 8, 747. [5] Chaudhuri, D. et al., Angew. Chem. Int. Ed. 2013, 52, 1. [6] Dias, F.B. et al. Adv. Mater. 2013, 25, 3707. [7] Hirata,S. et al., Nat. Mater. 2014, 13, 938. [8] Mani, T. et al., J. Phys. Chem. Lett. 2012, 3, 3115. [9] Ward, J.S. et al., Chem. Commun., 2016,52, 2612-2615

New approach to increase density of sensing units for higher precision as well as the selectivity of biological components under investigation in microcavity evanescent wave optical sensor systems is proposed. Long-term functionalization results of array sensor cells by different agents are represented.

Research on the surface chemistry of quantum dots (QDs) has been rapidly developing in recent years, since the understanding of the processes that occur on their surface is prerequisite for successful exploration of the outstanding fluorescence properties and superior stability of these nanomaterials in numerous applications. The lack of stability during long-term storage under atmospheric conditions restricts QD applications. Here, we have investigated the interaction of QDs with carbon dioxide as a model system for studying their long-term storage or operation in atmospheric environment. Quenching of the photoluminescence of CdSe/ZnS semiconductor QDs continuously treated with CO₂ has shown that this process depends on the type of the QD surface ligands. The luminescence of QDs capped with amine ligands is quenched to a higher degree, the quenching being caused by the formation of carbamic acid precipitate. The luminescence of QDs capped with thiols remain absolutely stable upon CO₂ treatment due to the chemical resistance of thiol functional groups to CO₂, which makes this type of QDs suitable for long-term storage and operation under atmospheric conditions. However, further functionalization of such QDs may be difficult, because the strong bond between thiol ligands and QD surface may limit the efficiency of ligand-exchange procedures. A new ligand system of alkylamine salts of fatty acids has been proposed as an alternative to thiols. It has been shown to be inert to CO₂, and also can be easily replaced with functional surface ligands. The results are important for development of nextgeneration QDs with superior stability suitable for various applications requiring efficient ligand exchange and operation in the atmospheric environment.

We describe the use of UV light under different radiation time induces a variety of fluorescence wavelength of gold quantum clusters. First, we synthesize blue-emitted gold quantum clusters by dissolving the gold trichloride in pure toluene. To simplify the expression, we assume that the several featured PL peak (425, 450, 470 nm) is the signal for blue-emitted gold quantum clusters. Undergo UV irradiation can brighten and broaden the PL spectra of gold quantum clusters, which are observed by the evolutional spectra versus exposure time. After UV light exposure, the major population of gold quantum clusters @425nm decreased and turned to gold quantum clusters@450nm, followed by the growing population of gold quantum clusters@470nm clusters. Until 2 hour exposure, the spectra become broad with major peak shifted to 525 nm. The tunable spectra from blue to green attributes to the induced growth of gold quantum clusters by UV irradiation. The UV energy indeed tunes and broadens the emission covering the whole visible-spectra range. Finally, we also utilize via proper selection of organic surfactant (such as: trioctyl phosphine, TOP) can coordinate the quantum yield enhancement of blue-emitted gold quantum clusters under UV irradiation. The experiment method is easily for gold quantum clusters synthesis. Thus we expect this materials can be developed for fluorescence labeling application in the future.

A local, low-energy, electrical method for the excitation of localized and propagating surface plasmon polaritons (SPPs) is attractive for both fundamental and applied research. In particular, such a method produces no excitation background light and may be integrated with nanoelectronics. Here we report on the electrical excitation of SPPs through the inelastic tunneling of low-energy electrons from the tip of a scanning tunneling microscope (STM) to the surface of a two-dimensional plasmonic lens. The plasmonic structure is a series of concentric circular slits etched in a thick gold film on a glass substrate. An out-going circular SPP wave is generated from the tip-sample junction and is scattered into light by the slits. We compare the resulting emission pattern to that observed when exciting SPPs on a thin, unstructured gold film. For optimized parameters, the light emitted from the plasmonic lens is radially polarized. We describe the effects of the slit period and number, and lens diameter on the emission pattern and we diskuss how the light beam of low divergence is formed.

This paper is devoted to experimental and theoretical studies of nonlinear propagation of a long-range surface plasmon polariton (LRSPP) in gold strip waveguides. The plasmonic waveguides are fabricated in house, and contain a gold layer, tantalum pentoxide adhesion layers, and silicon dioxide cladding. The optical characterization was performed using a high power picosecond laser at 1064 nm. The experiments reveal two nonlinear optical effects: nonlinear power transmission and spectral broadening of the LRSPP mode in the waveguides. Both nonlinear optical effects depend on the gold layer thickness. The theoretical model of these effects is based on the third-order susceptibility of the constituent materials. The linear and nonlinear parameters of the LRSPP mode are obtained, and the nonlinear Schrödinger equation is solved. The dispersion length is much larger than the waveguides length, and the chromatic dispersion does not affect the propagation of the plasmonic mode. We find that the third-order susceptibility of the gold layer has a dominant contribution to the effective third-order susceptibility of the LRSPP mode. The real part of the effective third-order susceptibility leads to the observed spectral broadening through the self-phase modulation effect, and its imaginary part determines the nonlinear absorption parameter and leads to the observed nonlinear power transmission. The experimental values of the third-order susceptibility of the gold layers are obtained. They indicate an effective enhancement of the third-order susceptibility for the gold layers, comparing to the bulk gold values. This enhancement is explained in terms of the change of the electrons motion.

The outstanding optical properties of Semiconductor Quantum Dots (QDs) have attracted much interest for over two decades. The development of synthetic methods for the production of core-shell QDs has opened the way to attaining almost ideal emitting properties. Their implementation in opto-electronic devices, such as light emitting diodes (LEDs) and lasers, requires a full understanding of the fine details of their photophysics. The exciton dynamics of core and coreshell QDs was extensively studied by means of pump and probe (P and P) and transient photoluminescence (TRPL) spectroscopies. Nevertheless, the wealth of possible exciton and multi-exciton decay mechanisms, operating on comparable time-scales, results in complex signals. In this work, the exciton dynamics of a complete CdSe/Cd_1-xZn_xS series is investigated, with a focus on exciton trapping processes. Insights into the energy distribution of exciton traps are unveiled by wavelength resolve QY measurements. Multicolor P and P measurements give a deeper insight into the dynamics of exciton trapping and Auger recombinations. An inversion method is proposed as a powerful tool for separating different contribution in complex P and P transients. The outcomes of this work clarify the role of core/shell interfaces and surfaces in modulating the optical properties and suggest possible routes for their improvement.

Metallic nanoparticles have been used as a way to tailor the fluorescence properties like quantum yield, but regular fluorescence quantum yield measurements have to counter the reflection and dispersion of a sample for an accurate result. Thermal lens spectroscopy is a good alternative to resolve this problem because doesn’t measure the fluorescence intensity but the heat generated by absorption. We studied the changes induced by silver nanoparticles, generated by laser ablation, in the fluorescence peak and quantum yield of Rhodamine B. We fund that the silver nanoparticles lowered the fluorescence peak and quenched the fluorescence of the Rhodamine B and how much is quenched also depends on its concentration.

Synthesis of quantum dots (QDs) in aqueous medium is advantageous as compared to the organic solvent mediated synthesis, as the aqueous synthesis is less toxic, reagent effective, easily reproducible and importantly, synthesized QDs have biological compatibility. The QDs should be aqueous in nature for use in cell imaging, drug labeling, tracking and delivery. Structural modifications are necessary to enable their use in biosensing application. In this work, mercaptopropionic acid capped cadmium telluride QDs (MPA-CdTe QDs) were synthesized by hydrothermal method and characterized by various techniques. Water and various biochemical buffers were used to study the fluorescence intensity stability of the QDs at different physicochemical conditions. QDs stored in 4° C showed excellent stability of fluorescence intensity values as compared to the samples stored at room temperature. Staphylococcal protein A (SPA) was conjugated with the QDs (SPA-QDs) and characterized using UV and fluorescence spectroscopy, zeta potential, HRTEM, FTIR, and AFM. Blue shift was observed in the fluorescence emission spectra that may be due to reduction in the surface charge as carboxyl groups on QDs were replaced by amino groups of SPA. This SPA conjugated to QDs enables binding of the C-terminal of antibodies on its surface allowing N-terminal binding site remain free to bind with antigenic biomarkers. Thus, the biosensor i.e. antibody bound on SPA-QDs would bind to the antigenic biomarkers in sample and the detection system could be developed. As QDs have better fluorescence properties than organic dyes, this biosensor will provide high sensitivity and quantitative capability in diagnostics.

Synthesis of nanotructured metal-carbon materials by laser irradiation is an actual branch of laser physics and nanotechnology. Laser sources with different pulse duration allow changing the heating rate with realization of different transition scenarios and synthesis materials with various physical properties. We study the process of the formation of nanostructured metal-clusters and complexes using laser irradiation of colloidal systems which were consisted of carbon micro- nanoparticles and nanoparticles of noble metals. For carbon nanoparticles synthesis we use the method of laser ablation in liquid. For the realization of different regimes of laser surface modification of the target (glassycarbon and shungite) and the formation of micro- nanoparticles in a liquid the YAG:Nd laser with a pulse duration from 0.5 ms up to 20 ms (pulse energy up to 50J) was applied. We have used the CW-laser with moderate intensity in liquid (water or ethanol) for nanoparticle of noble metals synthesis. Thus, colloidal systems were obtained by using CW-laser with λ = 1.06 μm, I ~ 10^5-6 W/cm², and t = 10 min. The average size of resulting particles was approximately about 10 to 100 nm. The nanoparticle obtaining was provided in the colloidal solution with different laser parameters. In this work we have investigated the mechanism of the metal-carbon cluster formation during the process of irradiation of colloidal system which were consisted of separate carbon, silver and gold nanoparticles. This system was irradiated by nanosecond laser (100 ns) with average power up to 50W.

Random laser actions in a disordered media based on ethylene glycol doped with Rh6G dye and Au nanorods have been demonstrated. It was observed that the size of Au nanorods strongly affects the pump threshold. The experiment results suggesting that the random lasing properties are dominated by the surface plasmons.

Experimental elastic-scattering characteristics of single evaporating liquid microdroplet of solution and suspension are reported. The microdroplets studied were composed of: (i) silica (SiO2) nanoparticles (225 nm radius) dispersed in diethylene glycol (DEG) liquid suspension (ii) DEG and Sodium dodecyl sulfate (SDS) solution, and (iii) SiO₂ nanoparticles dispersed in DEG and SDS solution. We observed regular Mie type fringes from (i), (ii) and (iii) at the initial stages of the evaporation process followed by intensity fluctuations (speckles) for (i) and surface reflections (blinking of scattered light intensities) for (ii) during the inclusions surface layer formation. For (iii), Mie-type fringes, and a mixture of surface reflections (blinking of scattered light intensities) and intensity fluctuations (speckles) was observed. The changes in the intensities and polarization of the scattered light showed characteristic stages of evaporation driven processes occurring at the droplet surface. The observed phenomenon carry information about the inclusions’ mean distances, size, and stages of aggregation of SiO₂ nanoparticles and crystallization of SDS nanocrystallites on the droplet surface. Additionally, we deposited samples of the final dried composite microobject on a silicon substrate and analyzed with SEM. The study provide different surface diagnostic methods of configuration changes in complex systems of nano-and microparticles evolving at the sub-wavelength scale and serves as an alternative method for studying stages of droplet with submicron inclusions evaporation processes.

Traditional fluorescent labelling techniques has severe photo-bleaching problem such as organic dyes and fluorescent protein. Quantum dots made up of traditional semiconductor (CdSe/ZnS) material has sort of biological toxicity. This research has developed novel Cd-free quantum dots divided into semiconductor (Indium phosphide, InP) and noble metal (Gold). Former has lower toxicity compared to traditional quantum dots. Latter consisting of gold (III) chloride (AuCl3) and toluene utilizes sonochemical preparation and different stimulus to regulate fluorescent wavelength. Amphoteric macromolecule surface technology and ligand Exchange in self-Assembled are involved to develop hydrophilic nanomaterials which can regulate the number of grafts per molecule of surface functional groups. Calcium phosphate (CaP) nanoparticle (NP) with an asymmetric lipid bilayer coating technology developed for intracellular delivery and labelling has synthesized Cd-free quantum dots possessing high brightness and multi-fluorescence successfully. Then, polymer coating and ligand exchange transfer to water-soluble materials to produce liposome nanomaterials as fluorescent probes and enhancing medical applications of nanotechnology.

A Grating Based hybrid-Plasmonic-waveguide with subwavelength optical-confinement is proposed which exhibits large-propagation-length with low-modal-propagation-loss. The Grating is formed in Si region by varying the grating period and duty cycle. The thickness of the grating region is 600 nm and the grating period is 700 nm. The mode is confined in the 10 nm SiO₂ region. The Si layer below the SiO₂ provides the large propagation length of 4 mm with low modal propagation loss of 1 dB/mm with subwavelength mode confinement 0.00079/ μm² is obtained.

We model the linear and nonlinear optical response of disk-shaped AlGaAs nanoantennas. We design nanoantennas with a magnetic dipole resonant mode in the near-infrared wavelength range, and we analyze volume second-harmonic generation driven by a magnetic dipole resonance by predicting a conversion efficiency exceeding 10^-3 with 1 GW/cm² of pump intensity.

We have precisely positioned and embedded a single gold nanoparticle (Au NP) into a desired polymeric photonic structure (PS) using a simple and low-cost technique called low one-photon absorption direct laser writing (LOPA DLW), with a two-step process: identification and fabrication. First, the position of the Au NP was identified with a precision of 20 nm by using DLW technique with ultralow excitation laser power (μW). This power did not induce the polymerization of the photoresist (SU8) due to its low absorption at the excitation wavelength (532 nm). Then, the structure containing the NP was fabricated by using the same DLW system with high excitation power (mW). Different 2D photonic structures have been fabricated, which contain a single Au NP at desired position. In particular, we obtained a microsphere instead of a micropillar at the position of the Au NP. The formation of such microsphere was explained by the thermal effect of the Au NP at the wavelength of 532 nm, which induced thermal polymerization of surrounding photoresist. The effect of the post-exposure bake on the quality of structures was taken into account, revealing a more efficient fabrication way by exploiting the local thermal effect of the laser. We studied further the influence of the NP size on the NP/PS coupling by investigating the fabrication and fluorescence measurement of Au NPs of different sizes: 10, 30, 50, 80, and 100 nm. The photon collection enhancements in each case were 12.9 ± 2.5, 12.6 ± 5.6, 3.9 ± 2.7, 5.9 ± 4.4, and 6.6 ± 5.1 times, respectively. The gain in fluorescence could reach up to 36.6 times for 10-nm gold NPs.

The limitation of conventional electronics is mitigated by all optical integrated circuits which have potential of high speed computing and information processing. In this work, an all optical AND gate using optical Kerr effect and optical bistability of a plasmonic based Mach-Zehnder interferometer (MZI) is proposed. An MZI is capable for switching of light according to the intensities of optical input signal. The paper constitutes with mathematical formulation of device and its study is verified using finite difference time domain (FDTD) method.

The resonance conditions of localized surface plasmon resonances (LSPRs) can be perturbed in any number ways making plasmon nanoresonators viable tools in detection of e.g. phase changes, pH, gasses, and single molecules. Precise measurement via LSPR of molecular concentrations hinge on the ability to confidently count the number of molecules attached to a metal resonator and ideally to track binding and unbinding events in real-time. These two requirements make it necessary to rigorously quantify relations between the number of bound molecules and response of plasmonic sensors. This endeavor is hindered on the one hand by a spatially varying response of a given plasmonic nanosensor. On the other hand movement of molecules is determined by stochastic effects (Brownian motion) as well as deterministic flow, if present, in microfluidic channels. The combination of molecular dynamics and the electromagnetic response of the LSPR yield an uncertainty which is little understood and whose effect is often disregarded in quantitative sensing experiments. Using a combination of electromagnetic finite-difference time-domain (FDTD) calculations of the plasmon resonance peak shift of various metal nanosensors (disk, cone, rod, dimer) and stochastic diffusion-reaction simulations of biomolecular interactions on a sensor surface we clarify the interplay between position dependent binding probability and inhomogeneous sensitivity distribution. We show, how the statistical characteristics of the total signal upon molecular binding are determined. The proposed methodology is, in general, applicable to any sensor and any transduction mechanism, although the specifics of implementation will vary depending on circumstances. In this work we focus on elucidating how the interplay between electromagnetic and stochastic effects impacts the feasibility of employing particular shapes of plasmonic sensors for real-time monitoring of individual binding reactions or sensing low concentrations – which characteristics make a given sensor optimal for a given task. We also address the issue of how particular illumination conditions affect the level of uncertainty of the measured signal upon molecular binding.

Structural and optical properties of TiO2 ALD coated silicon nanostructures were investigated. The morphology and chemical composition of TiO2 coated silicon nanopillars and porous silicon were studied by using methods of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Optical characteristics were studied using measurements of reflectance and luminescence spectra. Detailed analysis of morphological features and photoluminescence mechanisms were provided. Peculiarities of reflectance spectra were discussed. It was shown the possible application of these structures as antireflectance coatings.

Mask-aligner (MA) lithography is a well-known method for the fabrication of micrometer sized structures on a substrate with a diameter up to 300 mm. In spite of a theoretical resolution below 200 nm, the minimum printable feature sized remained above 1μm due to diffraction effects and limit its utilization to advanced packaging, or MEMS fabrication. Recently, developments in the illumination system and mechanical parts (known as AMALTIH for Advanced MA LITHography) as well as mask design, have permitted to used diffractive based photo-mask, and then reach the resolution limit mentioned above. This opens the possibility to fabricate smaller structures, usually accessible only by ebeam lithography. We propose here to demonstrate a fast and robust fabrication method of large area plasmonic absorber structures based on 2D sub-micrometric (350 nm period) nano-needles in a transparent polymer on a glass substrate and coated with a 50 nm thick gold layer. The interaction of the incoming light with metallic structured surface leads to the small total reflections of the 0th order below 5 %, over a large spectral band (460-660 nm) and a large set of incidence angles with TE and TM polarizations. Those results demonstrate that our fabrication process is a step toward the implementation of plasmonic based effect structures for a wide range of application.

Graphene Oxide (GO) has been prepared by modified Hummers method and it has been reduced using an IR bulb (800-2000 nm). Both as grown GO and reduced graphene oxide (RGO) have been characterized using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Raman spectra shows well documented Dband and G-band for both the samples while blue shift of G-band confirms chemical functionalization of graphene with different oxygen functional group. The XPS result shows that the as-prepared GO contains 52% of sp² hybridized carbon due to the C=C bonds and 33% of carbon atoms due to the C-O bonds. As for RGO, increment of the atomic % of the sp² hybridized carbon atom to 83% and rapid decrease in atomic % of C=O bonds confirm an efficient reduction with infrared radiation. UV-Visible absorption spectrum also confirms increment of conjugation with increased reduction. Non-linear optical properties of both GO and RGO are measured using single beam open aperture Z-Scan technique in femtosecond regime. Intensity dependent nonlinear phenomena are observed. Depending upon the intensity, both saturable absorption and two photon absorption contribute to the non-linearity of both the samples. Saturation dominates at low intensity (~ 127 GW/cm²) while two photon absorption become prominent at higher intensities (from 217 GW/cm² to 302 GW/cm²). We have calculated the two-photon absorption co-efficient and saturation intensity for both the samples. The value of two photon absorption co-efficient (for GO~ 0.0022-0.0037 cm/GW and for RGO~ 0.0128-0.0143 cm/GW) and the saturation intensity (for GO~57 GW/cm² and for RGO~ 194GW/cm²) is increased with reduction. Increase in two photon absorption coefficient with increasing intensity can also suggest that there may be multi-photon absorption is taking place.

Small particles tend to connect to each other and create large geometries, namely aggregates. To simplify the light scattering simulation process, they are usually modelled as assemblies of spheres positioned in point contact. This is a rough approximation because connections between them always exist. In this work we present answers to the three following questions: which optical properties of fractal-like aggregates are strongly dependent on the particle shape, what is the magnitude of the relative extinction error σC^ext when non-spherical particles are modelled as spheres and whether the relative extinction error σC^ext is dependent on the aggregate size N_p. The paper was aimed at tropospheric black carbon particles and their complex refractive index m was based on the work by Chang and Charalampopoulos. The incident wavelength λ varied from λ = 300nm to λ = 900nm. For the light scattering simulations the ADDA algorithm was used. The polarizability expression was IGT_SO (approximate Integration of Greens Tensor over the dipole) and each particle, regardless of its shape, was composed of ca. N_d ≈ 1000 volume elements (dipoles). In the study, fractal-like aggregates consisted of up to N_p = 300 primary particles with the volume equivalent to the volume of a sphere with the radius r_p = 15nm. The fractal dimension was D_f = 1:8 and the fractal prefactor was k_f = 1:3. Geometries were generated with the tunable CC (Cluster-Cluster) algorithm proposed by Filippov et al. The results show that when the extinction cross section σC^ext is considered, the changes caused by the particle shape, which are especially visible for longer wavelengths λ cannot be neglected. The most significant difference can be observed for the regular tetrahedron. The relative extinction error σC^ext diminishes slightly along with the number of primary particles N_p. However, even when large fractal-like aggregates are studied, it should not be considered as non-existent. On the contrary, when light scattering diagrams or the asymmetry parameter g are needed, spherical models can be used, even with relatively small fractal-like aggregates.

For the analysis of ZnO luminescence and the influence of surface plasmon resonance (SPR) on it the simplified approach is proposed. This approach is based on the set of rate equations (SRE), which describes processes taking part in the luminescence. The SRE includes the set of parameters that describe processes determining luminescence of an investigated sample. The proposed approach gives an opportunity for modeling the dependence of radiation intensity on pumping level and to estimate the values of parameters in SRE. As a result it is possible to make conclusions about peculiarities of samples and investigated processes. A number of experimental facts can be explained using this SRE, in particular the proposed approach was applied to consideration of insulating spacer role in ZnO/Ag system. It was shown that it is possible to interpret experimental results using SRE where values of some parameters depend on the spacer thickness. The proposed approach can be applied not only to ZnO-based structures but also to other emitters.

Optical Tweezers are capable of trapping individual particles of sizes that range from micrometers to sub micrometers. One can compute the trap strength experienced by a particle by analyzing the fluctuations in the position of the trapped particle with time. It is reported that the trap strength of a dielectric bead increases linearly with increase in the power of the trapping laser. The situation with metallic particles, however, is strongly dependent on the particle size. Available literature shows that metallic Rayleigh particles experience enhanced trap strengths when compared to dielectric particles of similar sizes due to a larger polarizability. On the contrary, micrometer sized metallic particles are poor candidates for trapping due to high reflectivity. We report here that commercially available micrometer sized metal oxide core - dielectric shell (core – shell) beads are trapped in a single beam optical tweezer in a manner similar to dielectric beads. However as the laser power is increased these core – shell beads are trapped with a reduced corner frequency, which represents a lowered trap strength, in contrast to the situation with ordinary dielectric beads. We attribute this anomaly to an increase in the temperature of the medium in the vicinity of the core – shell bead due to an enhanced dissipation of the laser power as heat. We have computed autocorrelation functions for both types of beads at various trapping laser powers and observe that the variation in the relaxation times with laser power for core - shell beads is opposite in trend to that of ordinary dielectric beads. This supports our claim of an enhanced medium temperature about the trapped core – shell bead. Since an increase in temperature should lead to a change in the local viscosity of the medium, we have estimated the ratio of viscosity to temperature for core – shell and dielectric beads of the same size. We observe that while for ordinary dielectric beads this ratio remains a constant with increasing laser power, there is a decrease for core – shell beads. We plan to extend this work towards studying the hydrodynamic correlations between a pair of trapped beads where one of the beads acts as a heat source.

The photoluminescence (PL) properties in GaN epilayers were investigated after depositing graphene quantum dots (GQDs) on the GaN surface. A seven-fold enhancement of the PL intensity in GaN was observed in the GQD/GaN composite. On the basis of the PL dynamics, the enhancement of PL in GaN is attributed to the carrier transfer from GQDs to GaN. Such a carrier transfer is caused by the work function difference between GQDs and GaN, evidencing by Kelvin probe measurement. The improved PL is promising toward applications in the GaN-based optoelectronic devices.

We analyzed and demonstrated the double layered metallic nano-structures using polystyrene lift-off process on the conventional surface plasmon resonance (SPR) sensor to enhance the sensitivity of an SPR surface. The double layered plasmonic structures are optimized using the three-dimensional finite-difference time-domain method for the width, thickness, and period of the polystyrene beads. The thickness of the metal film and the metallic nano-hole is 20 and 20 nm in the 305 nm wide nano-hole size, respectively. The double layered metallic nano-structures are fabricated with monolayer polystyrene beads of chloromethyl latex 4% w/v 0.4 μm. The sensitivities of the conventional SPR sensor and the double layered plasmonic sensor are obtained to 42.2 and 60 degree/RIU, respectively. The SPR devices are also applied to the lead ion sensor. The resonance shifts of SPR sensors with and without a poly(vinyl chloride) membrane are 1328 RU and 788 RU from 10^-5 M to 10^-2 M concentration, respectively.

Self-assembled silver, gold, and copper nanostructures on the monocrystalline GaAs (100) wafer surface were obtained via physical vapor deposition and characterized by optical reflection spectroscopy, scanning electron microscopy, and current-voltage curve measurements. Reflection spectra of the samples with Ag equivalent thicknesses of 2, 5, 7.5, and 10 nm demonstrated wide plasmonic bands in the visible range of spectra. Thermal annealing of the nanostructures led to narrowing of the plasmonic bands of Au and Ag nanostructures caused by major transformations of the film morphology. While the as prepared films predominantly had a small scale labyrinth structure, after annealing well-separated nanoislands are formed on the gallium arsenide surface. A clear correlation between films morphology and their optical and electrical properties is elucidated. Annealing of the GaAs substrate with Ag nanostructures at 100 °C under control of the resistivity allowed us to obtain and fix the structure at the percolation threshold. It is established that the samples at the percolation threshold possess the properties of resistance switching and hysteresis.

Two-Photon Polymerization (2PP) has become an established process for fabricating individual micro-and nanostructures nearly in the last two decades. Its high degree of freedom opened up novel possibilities for a large range of applications like functional structures for cell growth, photonic crystals, nanoantennas, diffractive optical elements and lab-on-a-chip structures (just to name a few). Since the measurement of structures written with 2PP is always very time consuming, we present a comparison between white light interferometry (WLI) and confocal microscopy (CM) which were used for measuring structures written with 2PP. By performing a GageRR analysis with both metrology devices, we calculated the process tolerance one has to accept when measuring these structures with WLI or CM.

A morphology and photoinduced changes of luminescence properties of two types of hybrid structures based on TiO₂ nanoparticles and CdSe/ZnS QDs were examined. A spin-coating method and a modified Langmuir- Blodgett technique have been applied to form the multilayer hybrid structures on glass slides. It was demonstrated that uniformity of QD surface concentration in hybrid structures depends on the method of structure formation. A photodegradation of luminescence properties of the structures is associated with the formation of QD aggregates. The QD aggregate concentration and their size depend on the method of the structure formation and the concentration of TiO₂ nanoparticles. A decay of luminescence of QD aggregates in hybrid structures contains a microsecond components. An exposure of the hybrid structures with uniform QD surface concentration by visible light resulted in a photopassivation of their surface, which is accompanied by significant increase of luminescence quantum yield of QDs.

Experimental investigation of circular dichroism (CD) spectra of complexes based on ZnS:Mn/ZnS and CdSe/ZnS QDs and chlorin e6 (Ce6) molecules in aqua solutions at different pH level, in methanol and in DMSO were carried out. The changes in CD spectra of Ce6 upon its bonding in complex with semiconductor QDs were analyzed. Application of CD spectroscopy allowed to obtain the CD spectrum of luminescent Ce6 dimer for the first time, and to discover a nonluminescent Ce6 aggregate, preliminary identified as a "tetramer", dissymmetry factor of which is 40 times larger than that for its monomer. The analysis of obtained data showed that in complexes with QDs Ce6 can be either in the monomeric form or in the form of non-luminescent tetramer. The interaction of relatively unstable luminescent Ce6 dimerwith QDs leads to its partial monomerization and formation complexes with chlorin e6 in monomeric form.

Stacked multi-layer films have a range of well-known applications as optical elements. The various types of theory commonly used to describe optical propagation through such structures rarely take account of the quantum nature of light, though phenomena such as Anderson localization can be proven to occur under suitable conditions. In recent and ongoing work based on quantum electrodynamics, it has been shown possible to rigorously reformulate, in photonic terms, the fundamental mechanisms that are involved in reflection and optical transmission through stacked nanolayers. Accounting for sum-over-pathway features in the quantum mechanical description, this theory treats the sequential interactions of photons with material boundaries in terms of individual scattering events. The study entertains an arbitrary number of reflections in systems comprising two or three internally reflective surfaces. Analytical results are secured, without recourse to FTDT (finite-difference time-domain) software or any other finite-element approximations. Quantum interference effects can be readily identified. The new results, which cast the optical characteristics of such structures in terms of simple, constituent-determined properties, are illustrated by model calculations.

We investigate a full-dielectric guided mode resonant photodiode. It has been designed to enhance the absorption by excitation of several resonances in the SWIR domain. The device consists of an InP/InGaAs/InP P-i-N heterojunction containing an active layer as thin as 90 nm on top of a subwavelength lamellar grating and a gold mirror. We successfully compared the electro-optical characterizations of individual pixels with electro-magnetic simulations. In particular, we observe near perfect collection of the photo-carriers and external quantum efficiency (EQE) of up to 71% around 1.55 μm. Moreover, compared with InGaAs resonator state-of-the-art detector, we show a broader spectral response in the 1.2-1.7 μm range, thus paving the way for SWIR low dark current imaging.

The optical transmission between two metalized optical fiber tips with sub-wavelength open apertures was studied for tip-to-tip distances down to ten nanometers. Transverse transmission maps with sub-wavelength structures clearly indicated optical near-field coupling. Depending on light polarization in the emission fiber tips one or two transmission peaks were observed. All these results were explained by a straightforward analytical model.

Using nanostructured thin metal films as colour filters offers several important advantages, in particular high tunability across the entire visible spectrum and some of the infrared region, and also compatibility with conventional CMOS processes. Since 2003, the field of plasmonic colour filters has evolved rapidly and several different designs and materials, or combination of materials, have been proposed and studied. In this paper we present a simulation study for a single- step lithographically patterned multilayer structure able to provide competitive transmission efficiencies above 40% and contemporary FWHM of the order of 30 nm across the visible spectrum. The total thickness of the proposed filters is less than 200 nm and is constant for every wavelength, unlike e.g. resonant cavity-based filters such as Fabry-Perot that require a variable stack of several layers according to the working frequency, and their passband characteristics are entirely controlled by changing the lithographic pattern. It will also be shown that a key to obtaining narrow-band optical response lies in the dielectric environment of a nanostructure and that it is not necessary to have a symmetric structure to ensure good coupling between the SPPs at the top and bottom interfaces. Moreover, an analytical method to evaluate the periodicity, given a specific structure and a desirable working wavelength, will be proposed and its accuracy demonstrated. This method conveniently eliminate the need to optimize the design of a filter numerically, i.e. by running several time-consuming simulations with different periodicities.

Metallic nanoparticles are important on several scientific, medical and industrial areas. The control of nanoparticles characteristics has fundamental importance to increase the efficiency on the processes and applications in which they are employed. The metallic nanoparticles present specific surface plasmon resonances (SPR). These resonances are related with the collective oscillations of the electrons presents on the metallic nanoparticle. The SPR is determined by the potential defined by the nanoparticle size and geometry. There are several methods of producing gold nanoparticles, including the use of toxic chemical polymers. We already reported the use of natural polymers, as for example, the agar-agar, to produce metallic nanoparticles under xenon lamp irradiation. This technique is characterized as a “green” synthesis because the natural polymers are inoffensive to the environment. We report a technique to produce metallic nanoparticles and change its geometrical and dimensional characteristics using a femtosecond laser. The 1 ml initial solution was irradiate using a laser beam with 380 mW, 1 kHz and 40 nm of bandwidth centered at 800 nm. The setup uses an Acousto-optic modulator, Dazzler, to change the pulses spectral profiles by introduction of several orders of phase, resulting in different temporal energy distributions. The use of Dazzler has the objective of change the gold nanoparticles average size by the changing of temporal energy distributions of the laser pulses incident in the sample. After the laser irradiation, the gold nanoparticles average diameter were less than 15 nm.

Photoinduced changes in luminescent and photoelectrical properties of the hybrid structure based on CdSe/ZnS QDs and multilayer graphene nanobelts were studied. It was shown that an irradiation of the structures by 365 nm mercury line in doses up to 23 J led to growth of QD luminescent quantum yield and photocurrent in the QD/graphene structures. This confirms the proximity of the rates of the QD luminescence decay and energy/charge transfer from QDs to graphene, and opens an opportunity to photoinduced control of the photoelectric response of the graphene based hybrid structures with semiconductor quantum dots.

Optical properties of composite structures comprised of the island films of silver nanoparticles with a thin molecular layer of a dye rhodamine 6G were obtained and studied in this paper. In the near field of plasmonic nanoparticles enhancement and shifting of the maximums of the absorption and fluorescence spectra were observed. In the absorption and fluorescence spectra of thin molecular films with nanoparticles the new red-shifted band in comparison with spectra of thin films without nanoparticles was found. This band was associated with the formation of aggregates. Thus, the silver nanoparticles can contribute to fluorescence enhancement and formation of the aggregates in the rhodamine thin films.

Recent research on hybrid plasmonic systems has shown the existence of a loss channel for energy transfer between organic materials and plasmonic/metallic structured substrates. This work focuses on the exciton-plasmon coupling between para-Hexaphenylene (p-6P) organic nanofibers (ONFs) and surface plasmon polaritons (SPPs) in organic/dielectric/metal systems. We have transferred the organic p-6P nanofibers onto a thin silver film covered with a dielectric (silicon dioxide) spacer layer with varying thicknesses. Coupling is investigated by two-photon fluorescence-lifetime imaging microscopy (FLIM) and leakage radiation spectroscopy (LRS). Two-photon excitation allows us to excite the ONFs with near-infrared light and simultaneously avoids direct SPP excitation on the metal layer. We observe a strong dependence of fluorescence lifetime on the type of underlying substrate and on the morphology of the fibers. The experimental findings are complemented via finite-difference time-domain (FDTD) modeling. The presented results lead to a better understanding and control of hybrid-mode systems, which are crucial elements in future low-loss energy transfer devices.

We investigate optical trapping light-absorbing particles in the air employing photophoretic forces with optical tweezers generated by a spatial light modulator (SLM). SLM gives us the opportunity to form optical tweezers for multiple trapping in several planes. We investigate the possibility of using lenses with various focal lengths for trapping light-absorbing microparticles with the SLM. We used lenses with a large focal length and a large depth of focus. The results shown in this paper could be useful in various applications of optics and biology.

In this paper we investigated the optical properties of a composite material consisting of a thin film of polymer doped by CdSe/ZnS quantum dots and silver nanoparticles on a transparent insulating substrate. It is found that in the presence of silver nanoparticles the quantum dots absorption is increased fivefold, the luminescence intensity is increased twelvefold while the luminescence lifetime is reduced.

Photoinduced dissociation of surface complexes of CdSe/ZnS quantum dots with azo-dye 1-(2- pyridylazo)-2-naphthol (PAN) was investigated. It was shown that the Förster resonance energy transfer contributes in the complexes photodissociation rate, which depends on resonance condition between electronic levels of donor (quantum dots) and acceptor (azo-dye) and donor photoluminescent quantum yield. It has allowed to estimate energy transfer efficiency in the complexes and disclosed a new nonradiative channel that has minor contribution in the deactivation of excited states of quantum dots in the complexes.

We use three dimensional finite-difference-time-domain simulations to study the dynamics of extraordinary optical transmission through arrays of nanoholes in 200 nm-thick Au films on silicon nitride substrates. By diving the light source into two identical 5 femtosecond pulses and tuning the relative delay between them, we are able to modulate both the intensity and spectra of the transmitted light on ultrashort time scales. Simulations demonstrate that the intensity and distribution of the electric fields on the surface of the film and within the nanoholes are altered by changing the pulse delay.

A physical model of compact generator producing short optical pulses with a controllable terahertz repetition rate is presented. The pulse generation is produced by modulation instability of surface plasmon polaritons in a structure with a silver film of subwavelength thickness.

Synthesis of transparent conductive coatings is a promising direction of modern nanotechnological research. Thin nanostructured noble-metallic films demonstrate nonlinear optical effects in visible spectral range because of their plasmonic properties [1]. In addition, optical characteristics of these thin films strongly depend on the period of the formed surface structures [2]. If the distance between deposited particles almost equals their sizes, the optical properties of the randomly deposited structures may considerably differ from these for periodical structures [3]. In this work, we have studied the degree of the morphology influence (particle diameter in the colloid, the distance between the deposited particles, the number of layers etc.) on the optical and electrical properties of the deposited thin film of bimetallic gold and silver clusters. In this work we used CW-laser with moderate intensity in liquid (water or ethanol) for synthesis nanoparticles of noble metals. For the formation of quasi-periodically arranged clusters, particle deposition from the colloidal systems is used. The optical properties of the deposited bimetallic films are shown to change as a function of composition and geometry in agreement with the modeling of the optical properties.

Susceptibility and polarization of two-level quantum dot (QD) with Coulomb correlations between localized electrons weakly connected to the reservoirs were carefully analyzed. It was revealed that both susceptibility and polarization depend strongly on high-order correlation functions of localized in QD electrons. It was demonstrated that susceptibility and polarization can be controlled by changing of applied bias voltage value, Coulomb correlations strength and Rabi frequency.

It has been demonstrated that photo-induced changes in the optical properties of semiconductor quantum dots (QDs) can be controlled by tuning the parameters of their laser irradiation to vary the relative contributions of photo-brightening and photo-darkening of QDs. For this purpose, the effects of the QD size, photon energy, and intensity of irradiation of QDs on the competing processes of photo-darkening and photo-brightening have been investigated. We have found that photo-brightening of QDs is not accompanied by detectable growth of their photoluminescence (PL) decay time, this process being most pronounced for QDs with an originally low PL quantum yield (QY). In this case, an increase in the PL QY is assumed to be caused by transition of some QDs from the dark (non-emissive) state to the bright (emissive) state. On the other hand, the photo-darkening effect, which was observed only under UV irradiation at 266 nm, was accompanied by simultaneous drop of both the QD QY and their PL decay time. We have also found that, at a constant dose of absorbed energy, the photo-brightening and photo-darkening processes do not depend on the excitation intensity. Thus, the photo-induced changes in the optical properties of QDs are one-photon processes. These data may help to optimize the QD operational conditions in practical applications requiring their intense excitation and add to understanding the fundamental mechanisms of the irreversible photo-induced changes that occur in colloidal QDs under illumination.

The optical properties of hybrid film based on plasmon Ag nanoparticles of different size and cyanine dyes with different length of conjugation chain depending on the relative position of the plasmon resonance and the absorption of organic molecules were studied. The absorption spectra of the films revealed several molecular forms, such as all-trans- and cisisomers, dimers and J-aggregate, which also exist in pure organic films without Ag nanoparticles. It’s shown that the absorption of aggregate bands increased after exposure by nanosecond laser on the hybrid films due to photo-induced additional self-organization of aggregates. In the presence of Ag nanoparticles, laser radiation leads to the change of molecular forms at a comparatively low threshold.

Within inharmonious plasma oscillation model the superconducting crystal AB is considered consisting of two subsystems 2AB=A2+B2. In high-temperature superconductors spontaneous division into two phases: superconducting and isolating was revealed. Phase separation was caused by plasma instability. It is obtained the transition superconducting phase temperature dependence T_c = F (q₁₂, q₁, q₂, V₁₂, V₁, V₂) on the isotopic substitution physical parameters: q – initial and component interaction parameters, V - volume in initial and component crystal lattices. The isotopic transition superconducting phase temperature displacement ΔT_c is associated with the change of the initial and component interaction and crystal lattice parameters. From the plasma mechanism of superconductivity follows superconducting crystals exist at room temperature.