We are using the technique of two-photon induced photoprecipitation to fabricate gold and silver nanostructures. Gold and silver nanoparticles are produced in solution as well as in thin films. In both cases an absorption peak associated with the plasmon resonance is clearly observed and is found to vary as particles grow. In addition, we show that this technique also permits the fabrication of 2D and 3D metallic nanostructures with a good quality. The potential for optical applications is discussed and illustrated on some examples. In particular, we observe high efficiency luminescence and strong tunable diffusion.

We investigate the local field spectroscopy of gold dimers by Two-Photon Photoluminescence (TPL) microscopy. A direct comparison with far-field scattering measurements shows that TPL provides additional data on the structure modes of major importance for their use in SERS, enhanced fluorescence and sensing.

The physical processes underlying the complex nanoscale optical responses of metal nanoparticles must be understood both experimentally and theoretically if they are to be developed for use in photonic devices. While many linear optical measurements have been performed on gold nanoparticle arrays, only a handful of nonlinear measurements have been reported. Here, we discuss a collection of experiments of both types on arrays of gold nanoparticles. However, on nanoscale-rough metal surfaces, such as nanoparticles with small-scale defects, local electric fields may vary rapidly and strong field gradients can induce significant multipolar contributions, making a theoretical description of second-harmonic generation (SHG) from nanoparticle arrays infeasible at present. A macroscopic nonlinear response tensor approach based on the input and output fields to the system avoids with these complications. Contributions from higher multipoles are implicitly included, and electric-dipole-type selection rules can be applied to address symmetry issues. While the experimental geometry constrains the formalism, additional insight into the underlying physical processes is expected from experimental variations. Good agreement with direct SHG tensor measurements validates the formalism, providing the framework for a deeper understanding of the nanoscale optical responses of metal nanoparticles.

We present the results of the experimental studies of nonlinear-optical and nonlinear magneto-optical properties of granular magnetic films exhibiting giant magnetoresistance effect. The samples under study are Co-containing nanogranular films of the composition (Co)_x(Al₂O₃)_1-x, the concentration of cobalt, x, being varied in a wide range. A strong azimuthal anisotropy in the intensity of the second (SHG) and third harmonics (THG) is observed which proves the anisotropic crystallographic structure of granular films. The nonlinear magneto-optical Kerr effect (NOMOKE) in SHG and THG is studied in the films for the geometry of the transversal magnetization. The dependence of the NOMOKE contrast in the SHG (THG) intensity is found to be a non-monotonous function of Co content in the films. The dependence of the magnetization-induced components of the quadratic susceptibility on the content of Co in the films is estimated.

The European Patent Office has created a nanotechnology initiative in order to continue to ensure the granting of high-quality patents while coping with the increasing workload and with the multidisciplinarity of the inventions in this area of technology. The classification work in the field of nanotechnology is outlined with special emphasis on the sub-discipline of nanophotonics.

We demonstrate the use of interference between non-diffracting Bessel beams (BB) to generate a system of optical traps. They offer sub-micron particle confinement, delivery and organization over a distance of hundreds of μm. We analyze system of two identical counter-propagating BBs and the case of two co-propagating BBs with different propagation constants separately. In both of these cases, the interference results in periodic on-axis intensity oscillations involving particle confinement. Altering the phase of one of the interfering beams, the whole structure of optical traps can be shifted axially. Implementing this conveyor belt enables the particle delivery over the whole distance where the optical traps are strong enough for particle confinement. Experimentally we succeeded with generation of both of these systems. In case of two counter-propagating BBs we observed a strong sub-micron particle confinement, while in case of co-propagating BBs the confinement was observed only with help of fluid flow against the radiation pressure of both beams.

We present the multi trap optical tweezers system that enables to generate two-dimensional dynamical configurations of focal spot where the trapping force of each element can be individually changed. We apply the system to investigate how substrate rigidity affects the strength of the integrin-extracellular matrix adhesion in living cells. Adhesion sites of different rigidity are mimicked by simultaneously attaching on cell cortex beads held by optical traps of different stiffness. We monitor the effect induced by the local rigidity on cell adhesion by looking at vinculin recruitment in GFP-Vin transfected HeLa cell. To this end the optical tweezers system is inserted in an epifluorescence inverted microscope.

In this paper we elucidate the peculiar behaviour of optically bounded micron-sized objects. For these studies we have modified algorithm based on the coupled dipole method (CDM), which is currently the most effective tool for the analysis. We present how to simulate the optical binding of two dielectric spheres placed in two counter-propagating non-interfering Gaussian laser beams. The results give us an insight into the background of forces acting between optically bound particles concerning the phenomenon of multi-stable particle separations.

We investigate simultaneous optical trapping and optical detection of a single Rb atom near the surface of a toroidal microdisk. Light is coupled into two high-Q whispering-gallery modes of the disk which provide attractive and repulsive potentials, respectively, via their evanescent fields. The sum potential including van-der-Waals and Casimir-Polder surface forces exhibits a minimum at distances of the order of 100 nm from the disk surface. The back-action of an atom held in this trap on the light fields is sufficiently strong to provide a measurable effect. We discuss atom trapping and detection properties in dependence on a variety of system parameters.

Rigorous numerical simulations of Maxwell's equations are extremely helpful in the understanding of physical effects in nano-optics and are essential for the design of nano-optical devices. We have developed a finite-element (FEM) package for the solution of eigenvalue and scattering problems resulting from Maxwell's equations. We have implemented higher order vectorial elements, adaptive mesh refinement, transparent boundary conditions based on the Pole condition, and fast algorithms. In this contribution we discuss the application of the FEM solvers to recent experiments in nano-photonics.

We have performed Finite Element Electromagnetic modeling of light scattering in 'apertureless' Scanning Probe Optical Microscopy. Metal tips above metallic and transparent surfaces were modeled to determine suitable conditions for Tip-Enhanced Raman Spectroscopy (TERS) and fluorescence. Gold, silicon, and oxidized silicon were evaluated as potential tip materials, as were the widely used flat substrates of gold, mica and silicon. The lateral resolution of optical imaging is calculated, as a function of tip-substrate separation. This resolution can be made significantly smaller than the tip radius for small tip-substrate separations. In order to model biologically relevant samples, aqueous environments are investigated for the first time, yielding some surprising results.

We present a wide, theoretical study of the emission of a point source (a quantum dot) in various waveguides: fully dielectric, perfect-conductor-coated, gold-coated and based on photonic crystal. This study aims at determining the most suitable structures to suppress the emission into the radiative modes or equivalently to channel most of the emission into a single guided mode. We conclude that the structures, which exhibit the highest β-factor, are promising devices for photonic applications.

Conventional lithography is a leading high-throughput patterning method for mass production. But the dramatically increasing cost of lithographic equipment and mask sets, which is a consequence of pushing optical lithography to its limits, makes alternative, maskless lithographic techniques attractive. Femtosecond lasers have been found suitable for processing of a wide range of materials with sub-micrometer resolution. The limit of achievable structure sizes is predicted to be below 100 nm. Therefore, it is attractive to use this technique for maskless lithography. In this paper, first results on super-resolution femtosecond laser lithography showing great potential for future applications are presented.

We report on the electromagnetic interactions between a two-dimensional periodic arrangement of resonant gold nanoparticles and a flat gold metallic film. We observe multi-peaks in the extinction spectra attributed to resonant modes of the hybrid system, resulting from the coupling between the Localized Plasmon of the nanoparticles with the underlying Surface Plasmon Mode. Simulations based on the Fourier modal method give good agreement with the experimental measurements and allow for the identification of the respective contributions.

Nanowire composites are considered as a challenge in designing and making a negative index materials. By controlling the distance between parallel nanowires the electric and magnetic resonances of this structure are forced to spectrally coincide. Measurements of amplitude and phase of fabricated samples are provided together with theoretical results.

We homogenize a 2D dielectric photonic crystal by means of a multiple scale approach. We show that if the rods constituting the crystal have Mie resonances at large enough wavelengths, the crystal presents an effective permeability exhibiting anomalous dispersion. When embedding in a negative permittivity medium, this leads to a negative index material.

We present an experimental system based on the use of a spatial light modulator which enables to perform simultaneously 3D optical manipulation and optical sectioning. This has been achieved by modifying the wave front of the trapping beam with properly diffractive optical elements displayed on a computer controlled spatial light modulator. We demonstrated the capability of the system in two experimental schemes, in a first one we performed a 3D optical scanning of 6 trapped beads by displacing the beads through a fixed imaging plane. In a second one we scan the imaging plane and simultaneously compensate for the movement of the objective in order to keep the trapping plane at a fixed position.

We discuss in this paper some general properties of magnetic photonic crystals with simple cubic lattice. Using the theory of magnetic groups, we consider the problem of changing symmetry of photonic crystal with simple cubic lattice by a dc magnetic field and qualitative characteristics of their eigenwaves. The analysis is fulfilled using symmetry arguments alone.

Excitation and cancellation of higher-order elegant Hermite-Gaussian and Laguerre-Gaussian beams under normal incidence at isotropic, lossless, dielectric interfaces are analysed. It is shown that such phenomena are originated in the cross-polarization coupling between orthogonal polarization components of the beams and depend qualitatively on interrelations between beam field spatial distribution and beam polarization. For Laguerre-Gaussian beams these interrelations associate beam orbital and spin angular momenta. Analytic description confirmed by numerical simulations is given for transmission of two types of beams: Hermite-Gaussians of linear polarization and Laguerre-Gaussians of circular polarization.

This presentation describes several important applications of steady-state and time-resolved photoluminescence (PL) instrumentation in the field of nanophotonics. The paper presents a cohesive overview of PL instrument configurations and data analysis methods pertaining to each of the described nanophotonics applications. Key nanomaterials in the nanophotonics field include carbon nanotubes, organic light-emitting diodes and quantum dots. Highlighted carbon nanotube applications focus on the steady state excitation-emission matrix analyses of the semiconducting properties of single-walled nanotubes (SWNTs); these properties are relevant to the implementation of SWNTs in nanophotonics circuitry and high-definition display technology. Quantum dots (QDOTS) are also becoming increasingly important for nanophotonics applications including steady state and time-resolved measurements pertaining to biosensing, tunable bandgap circuitry and cancer imaging-diagnostics. Organic light emitting diodes (OLEDS) are now also recognized for their potential uses in novel display technology and time-resolved PL applications are described as key tools in the OLED research and development arena. The presentation will conclude with a summary of the perceived future of the industrial applications and scientific progress in developing areas of nanophotonics PL.

If semiconductor quantum dots are to be incorporated into hetero-structural devices such as light emitting diodes it is important to understand the influences of the surrounding medium on the properties and particularly the photoluminescence of the nanocrystals. Here we investigate the temperature dependence of emission from CdTe quantum dots in aqueous solution with capping layers of thioglycolic acid. Results from quantum dots both held in suspension and deposited as thin films are shown. In both suspensions and thin film multilayers a reversible spectral shift to lower energy is seen with increasing temperature. This red shift of photoluminescence is thought to be the result of increased exciton carrier transfer between the quantum dots at higher temperatures and the thermal activation of emission from lower energy trap states. Both suspension and thin film devices also show a recoverable loss in photoluminescence intensity when the sample is heated. These changes are explained by the thermal activation of nonradiative surface traps. Finally, an irreversible loss in photoluminescence is reported in the CdTe thin film devices and to a lesser extent also in the quantum dot suspensions. This observation is explained by the heat induced formation of agglomerates imaged by AFM analysis.

A microscopic model for surface-enhanced Raman scattering (SERS) from molecules adsorbed on small noblemetal nanoparticles is developed. In the absence of direct overlap of molecular orbitals and electronic states in the metal, the main enhancement source is the strong electric field of the surface plasmon resonance in a nanoparticle acting on a molecule near the surface. In small particles, the electromagnetic enhancement is strongly modified by quantum-size effects. It is shown that, in nanometer-sized particles, SERS magnitude is determined by a competition between several quantum-size effects such as the Landau damping of surface plasmon resonance and reduced screening near the nanoparticle surface. Using time-dependent local density approximation, the spatial distribution of local fields near the surface and enhancement factor for different nanoparticles sizes are calculated.

We demonstrate the association of two-photon nonlinear microscopy with balanced homodyne detection for investigating second harmonic radiation properties at nanoscale dimensions. Variation of the relative phase between second-harmonic and fundamental beam is retrieved, as a function of the absolute orientation of the nonlinear emitters. Sensitivity of ≈ 1.6 photon per second, in the spatio-temporal mode of the local oscillator, is obtained. This value is high enough to efficiently detect the second-harmonic emission from a single KTiOPO₄ crystal of sub-wavelength size, embedded in a thin polymer film.

Plasmonics applications will benefit if reliable means to alter plasmon absorption and damping properties via external inputs are found. We are working towards this goal by functionalizing noble metal films with polarizable, excitonic molecular films. Examples include molecular j-aggregates, whose excitonic absorptions can be photobleached to modify plasmon absorption properties. We report two developments in this area. The first is the observation of coherent polarization coupling between the exciton of a molecular J-aggregate and the electronic polarization of noble metal nanoparticles. The second is a new far-field method to directly observe surface plasmon propagation, demonstrating that the lateral intensity decay length is affected by a change of the interface property. The method relies on the detection of the intrinsic lossy modes associated with plasmon propagation in thin films. We also uniquely introduce a method to excite a broad spectral distribution of surface plasmon simultaneously throughout the visible spectrum allowing surface plasmon based spectroscopy to be performed.

Photonic and plasmonic structures and devices have attracted a lot of attention during the last years, promising many scientific and technological applications, e. g. in information technology, sensing and detection, and optical data storage. Especially, the rapidly growing field of surface plasmon polaritons (SPP) promises unique integration of microelectronic devices with optics on the microscale. In this contribution, we discuss applications of advanced femtosecond laser technologies for the fabrication of high quality 2D and 3D photonic and plasmonic structures. We present our results on the construction of 3 dimensional photonic crystals by two-photon-polymerization (2PP) technique and optical characterization of these crystals. Furthermore, we show the capability of 2PP in building of 2-dimensional structures for guiding and manipulation of SPPs. Focusing of SPPs at dielectric structures fabricated by 2PP on metal surfaces is demonstrated. Waveguides, splitters, and couplers for application in plasmonics are also fabricated by this technique.

A simple technique to prepare large-area, regular microstructures in glass containing silver nanoparticles is presented. Here the modification of spatial distribution of the nanoparticles is achieved using a direct current (DC) electric field at moderately elevated temperatures. The technique exploits the recently reported effect of "electric field-assisted dissolution" (EFAD) of silver nanoparticles during which the silver nanoparticles embedded in a glass matrix can be destroyed and dissolved in the glass in form of Ag⁺ ions by a combination of an intense DC electric field (~1kV) and moderately elevated temperature (~280°C). This process can lead to a total transparency of the nanocomposite glasses, which to our knowledge can not be achieved via any other technique. In this work, the possibility to produce orderly-oriented array of embedded, 2-D, micron size optical structures in silver-doped nanocomposite glass is demonstrated. This could lead to an easy way for production of many useful optical devices based on the composite materials.

Small metal nanostructures, especially gold and silver nanoparticles, are known for their interesting optical properties caused by plasmons. Isotropic or anisotropic, homogeneous or heterogeneous metal nanoparticles provide a platform for different highly defined functional units with interesting optical properties for applications such as waveguides or (in combination with molecular parts) molecular beacons. We combined such nanoparticles with sub-wavelengths apertures in metal films, and studied the effect of the presence of particles in these nanocavities on the topography as well as on the optical behavior. Therefore, methods were developed that allow for a correlation of topography and optical properties. The transmission through the holes was clearly influenced by the presence of nanoparticles. Combined with the potential of designing the plasmonic properties of particles by customized diameters as well as composition using core-shell techniques, this approach promises an interesting novel class of plasmonic nanostructures.

Interest in photonic nanodevices motivates search for efficient transport of energy in plasmon waveguides. Chains of silver nanoelements guide light in channels of below-the-diffraction-limit size due to surface plasmon coupling. We calculate attenuation factors in chains with several geometries of nanoplates using the Finite Difference Time Domain (FDTD) method for visible and near infrared range of wavelengths, where the Drude model of dispersion is valid. Nanoplates considered in simulations are 1 micrometer high, 50 nm thick and 380 nm long and are embedded in a medium with refractive index reaching n = 1.5. Advantages of proposed waveguides are connected with their small size and possible tuneability by adjustment of geometrical parameters. However, the waveguides highly attenuate signals due to radiation into the far field and internal damping. For the optimum considered geometry and 595 nm wavelength, the energy transmission of 2 micrometers long chain of parallel nanoplates reaches 39%.

In combining time-resolved two-photon photoemission (TR-2PPE) and photoemission electron microscopy (PEEM) the ultrafast dynamics of collective electron excitations in silver nanoparticles (localized surface plasmons - LSP) is probed at femtosecond and nanometer resolution. In two examples we illustrate that a phase-resolved (interferometric) sampling of the LSP-dynamics enables detailed insight into dephasing and propagation processes associated with these excitations. For two close-lying silver nano-dots (diameter 200 nm) we are able to distinguish small particle to particle variations in the plasmon eigenfrequency, which typically give rise to inhomogeneous line-broadening of the plasmon resonance in lateral integrating frequency domain measurements. The observed spatio-temporal modulations in the photoemission yield from a single nanoparticle can be interpreted as local variation in the electric near-field and result from the phase propagation of the plasmon through the particle. Furthermore, we show that the control of the phase between the used femtosecond pump and probe laser pulses used for these experiments can be utilized for an external manipulation of the nanoscale electric near-field distribution at these particles.

In contrast with aperture-limited Scanning Near-field Optical Microscopy, where the focusing of light is achieved only with very high attenuation, in apertureless near-field optics light is both focused and strongly amplified by the surface plasmons of the probe. Although the general feasibility of this idea and the unprecedented in optics lateral resolution of ~ 15-30 nm have already been demonstrated, the actual field enhancement has so far been well below theoretical expectations, and the useful optical signals have been weak. To bridge the gap between the "proof-of-concept" experiments and reliable optical microscopy with molecular-scale resolution, one needs to unify accurate simulation with effective measurements of the optical properties of the tips and with fabrication. We use dark-field microscopy with side collecting optics for measurements of the optical properties of the tip. The side view allows us to observe the radiation of the tip and hence to analyze its optical properties at the apex. In addition, the measured Raman signal provides an estimate of the electric field enhancement by the tip. Our simulation protocol consists of two parts: electrostatics and wave analysis. Electrostatic simulations give good qualitative predictions, are very fast and therefore conducive to multiparametric optimization. Full wave analysis is needed to evaluate the dephasing effects and far-field signals. The Finite Element Method is used for all simulations. Various tip designs with the field enhancement ranging from ~ 50 to over 250 (depending on various parameters), with the commensurate enhancement of the Raman signal by ~ 45⁴ (for gold coating) and ~ 270⁴ (for silver coating), are presented and analyzed.

This paper deals with an efficient computation method for scattered light intensity distributions, which occur, if a nanostructured surface is illuminated with a monochromatic laser beam of several millimeters in diameter. The minimization of the computational amount is an essential precondition in connection with the development of powerful design tools for laser optical surface measuring methods, which derive structure characterizing attributes from structure dependent scattering effects. The presented approach differs from concepts based on near-field solutions of the Maxwell equations (finite element methods (FEM), finite difference time domain methods (FDTD)) or approximation methods for the near-field (Discrete Dipole Approximation (DDA), Generalized Multipole Technique (GMT)) as the near-field is not computed. Instead, an electrically equivalent model based on pre-computed radiation sources like Huygens point sources, dipoles, quadrupoles, etc. is used, which for standard geometrical nanostructures (cylindrical holes, spheres and ellipsoids) leads to the same far-field distributions as the conventional methods. In order to simulate the scattered light by an arbitrary surface it is divided into subwavelength geometries, which can be substituted by electrically equivalent dipole radiation sources. The far-field is calculated with a numerical scalar method. The computational effort is much smaller compared to algorithms based on the solution of Maxwell's equations.

The Si/SiO₂ superlattices were prepared by a molecular beam deposition method, high temperature furnace annealing (1100 °C), and back-side Si wafer etching in tetramethyl ammonium solution. Transmission electron microscopy and Raman spectroscopy show that the layered structure is not preserved during high temperature treatment. The etching of the substrate increases photoluminescence of the Si/SiO₂ material. Optical waveguiding was realized for the free-standing sample demonstrating its reasonable optical quality and providing the optical parameters.

Chemical approaches allow for the synthesis of highly defined metal hetero-nanostructures, such as core-shell nanospheres. Because the material of metal nanoparticles determines the plasmon resonance-induced absorption band, the control of particle composition results in control of the position of the absorption band. Metal deposition on gold or silver nanoparticles yielded core-shell particles with modified optical properties. Besides the optical characterization, the utilization of AFM and TEM yielded important information about the morphology of the nanoparticle complexes. UV-vis spectroscopy on solution-grown and surface-grown particles was conducted as ensemble measurements in solution. Increasing layers of a second metal lead to a shift in the absorption band, and a shell diameter comparable to the original particle diameter leads to a predominant influence of the shell material. The extent of shell growth could be controlled by reaction time or the concentration of either the metal salt or the reducing agent.

This paper presents a simulation approach for light scattering from surfaces containing spherical and elliptical nanoparticles. For this approach an electrically equivalent macro model is derived based on the analytical solutions of Maxwell's equations (e.g. Mie's solution of a sphere). These macro models do not necessarily fulfill the boundary conditions or give the correct near-field but they provide a suitable far-field solution. The benefit of this approach is an abstract model for the far-field computation that is much more efficient than known solutions like FEM. The radiation sources at the surface are reduced to a maximum like a single source for a whole particle, which gives the correct far-field but does not fulfill the boundary conditions. For the set of radiation sources used for the macro models the approach presented here reverts to the accurate computation of simple geometries. In this special case of spherical and elliptical particles the solution of the Mie theory can be used. In this paper it is shown that in the case of nanostructures the far-field of a sphere and an ellipse can be replaced by the radiation field from a set of dipoles. Based on these results it is possible to approximate an equivalent macro model of the surface containing spherical and elliptical elements. The presented macro model provides a very reasonable simulation approach with acceptable simulation times for large surface areas of several square millimeters.

Electroluminescence of the CO₂ laser annealed PECVD-grown silicon-rich silicon oxide (SRSO) based metal-oxide-semiconductor diode with embedded Si nanocrystals is demonstrated. The structural and optical properties of a CO₂ laser rapid thermal annealed Si-rich SiO_1.25 film are investigated. The color of SiO_1.25 film changes from light yellow to dark-yellow as the CO₂ laser annealing intensity enlarges from 1.5 to 13.5 kW/cm². Such a color change is mainly attributed to both the increasing absorption coefficient and refractive index of the SiO_1.25 film under the precipitation of Si nanocrystals. The thickness of the SiO_1.25 film was thinned during the dehydrogenated process at a slightly lower laser intensity of 4 kW/cm², while the complete dehydrogenation is observed after annealing for 1.4 ms associated with a thickness shrinking from 280 nm to 240 nm. TEM analysis and photoluminescence spectroscopy at 806 nm reveal that the Si nanocrystals with maximum diameter and density of 5.3 nm and 10¹⁸ cm^-3, respectively, can be precipitated as the CO₂ laser intensity increase to an ablation threshold intensity of 5.8 kW/cm². The laser ablation introduces numerous structural defects and causes the anomalous absorption as well as photoluminescence at blue-green wavelengths in the SiO_1.25 film. From the reflection spectra with enlarged interfering fringe amplitude, the increasing refractive index (from 1.57 to 1.88) of the SiO_1.25 with increasing laser intensity can be concluded. In comparison with that of the quartz or as-grown sample, the red-shifted optical bandgap energy of the CO₂ laser-annealed SiO_1.25 film from 5.4 eV to 4 eV has evidenced the effect of the strong blue-green absorption on the oxygen vacancy defect. The forward turn-on voltage and current density of the ITO/CO₂ laser annealed SRSO/p-Si/Al MOS diode are 79 V and 33 μA/cm², respectively. The maximum output power of 29 nW associated with a P-I slope of 4.4 mW/A is determined.

Based on the developed method of self-consistent calculations the results of description of tunable optical spectra versus temperature and excitation level for the GaSb doping superlattices of different design are presented. Account of the appearing tails of the density of states allows describing the long-wavelength edges and shape transformation in the spectra of absorption, gain, and luminescence and peculiarities in the optical transitions characteristics. Possible laser diode structures with n-i-p-i crystals in the active region are suggested including ordinary and δ-doped superlattices. Effects of tunable lasing are examined and ways for control of the radiation wavelength are discussed.

Despite of the fact that in the last years a significant effort have been devoted to pulsed laser ablation (PLA), the problem of micro and nanoparticles have not been unambiguous presented (to our knowledge). In this work, we studied the size, size distribution and structure of the particles produced by laser ablation and luminescence as well. Scanning and transmission electron microscopy, X-ray diffraction and optical spectroscopy have been used. The investigations were made on Si/SiO₂ nanopowders as produced, without any post-treatment (chemical, thermal, etc.). The experimental parameters were: silicon target, laser wavelength 355/532 nm, pulse duration 5 ns, repetition rate 10 Hz, fluence 4-8 J/cm², argon/helium, 250-550 mbar, flow rate 1 l/min. Our investigations have shown that the particles are distributed in two main classes: one, with the size 0.1-1 μm, and the other with the diameter less than 14 nm. Our evaluation for optimal experimental conditions shown that around 78% (vol.) of particles are < 10 nm and almost 50% have diameters in the range 2-5 nm. The photo and cathodoluminescence were in the range 400-1000 nm, with main peak at 690-725 nm.

Using third and forth order perturbation, we have derived main GaAs band parameters (such as E_P) from both experimental results (m^*, g^*, ...) and theoretical results (overall band structure from Cohen-Chelikowski pseudo-potential calculations). The analysis of the set of data leads to a drastic change to the "admitted" value of some parameters (E'_P) from the only experimental results and show inconsistency if theoretical results are furthermore taken into account.

We report on a nearly isothermal, reversible transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. The phase transition phenomenon and the related unidirectional mass-transport effect are caused by optically driven molecular motion of azobenzene-functionalised molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. We also show that the selective excitation of chromophores by linear polarized light induces an anisotropic expanding force, which can be used for polarization-selective opto-mechanical actuators and sensors. Moreover, since the molecular motions can be induced also by spatially confined non-propagating optical fields, we are able to manipulate the state and position of nanoscopic elements of matter using optical near-field approaches.

Although coherent light is usually required for the self-organization of regular spatial patterns from optical beams, we show that peculiar light matter interaction can break this evidence. In the traditional method to record laser-induced periodic surface structures, a light intensity distribution is produced at the surface of a polymer film by an interference between two coherent optical beams. We report on the self-organization followed by propagation of a surface relief pattern. It is induced in a polymer film by using a low-power and small-size coherent beam assisted by a high-power and large-size incoherent and unpolarized beam. We demonstrate that we can obtain large size and well organized patterns starting from a dissipative interaction. Our experiments open new directions to improve optical processing systems. We also discuss the relevance of our experiment to other systems such as social insects, for which a self-assembly or spatial pattern is organized within a collective group, starting from amplified fluctuations.

An example of near-field Raman spectroscopy based on the tip-enhancement at an apertureless tetrahedral scanning near-field optical tip (t-tip) is presented. Tip-enhanced Raman spectroscopy (TERS) is based on the excitation of localized surface plasmons (LSP) in the cavity of tip and surface. The LSP provide a highly confined and large field enhancement at the tip apex which allows molecular spectroscopy at the nanoscale. The t-tip consists, in contrast to other TERS configurations which use opaque tips, of a gold coated glass tip which is irradiated from the inside. We demonstrate TERS spectra of the dye malachite green isothiocyanate and show an increased bleaching of the dye in presence of the tip. Data analysis show that the actual experimental conditions support moderate enhancement of the Raman signal.

In device engineering, a high degree of supramolecular organisation is required to achieve certain desired macroscopic properties. Dye-loaded zeolite L host-guest materials have been successfully used in the realisation of efficient light-harvesting antenna systems. A new hierarchy of structural order is introduced by arranging the zeolite L crystals into densely packed, oriented monolayers on a substrate. We developed methods to synthesise such monolayers, to fill them with dyes and to terminate them with a luminescent stopcock. By the subsequent insertion of different types of dye molecules in a zeolite L monolayer, the first unidirectional antenna system was realised. Such antenna materials open possibilities for the design of a novel thin layer, silicon based solar cell, where the excitation energy can only migrate in one direction towards the zeolite-semiconductor interface. The electronic excitation energy is then transmitted to the semiconductor by Forster resonance energy transfer (FRET) via stopcock molecules attached to the channel ends. Direct transfer of electrons is prevented by an insulating layer. We report here on the UV-VIS absorption as well as NIR luminescence spectroscopy results obtained from such materials.

We investigate the mechanisms for fluorescence enhancement and energy transfer near a gold tip in apertureless scanning near-field optical microscopy (ASNOM) and provide a demonstration of sub-diffraction tip-enhanced fluorescence imaging. We have imaged the fluorescence from a single quantum dot cluster using ASNOM and find that when a sharp gold tip is brought within a few nanometres from the sample surface, the resulting enhancement in quantum dot fluorescence in the vicinity of the tip leads to a resolution of about 60 nm. We determine this enhancement of the fluorescence to be about four-fold in magnitude, which is consistent with the value calculated with a simple quasistatic model. Using this model we show that the observed enhancement of fluorescence results from a competition between enhancement and quenching, dependent on a range of experimental parameters. We also demonstrate that optical signals measured in ASNOM under ambient conditions are found to be affected significantly by the thin water layer absorbed on the surface under investigation.

Resonance energy transfer (RET) is a near-field mechanism for propagating optical energy between particles with suitably matching frequency response. The process communicates electronic excitation between suitably disposed (donor and acceptor) dipoles in close proximity, activated on excitation of the donor. In a multi-component system the transfer of excitation between any given donor and acceptor is usually passive, and it competes with loss mechanisms such as radiative decay and the possibility of transfer to one or more other acceptors. It thus appears that any potential exploitation of RET for optical switching is compromised by the innate passivity of the process. Now it emerges that there is a direct, all-optical route to introduce the necessary control. In a system constructed to satisfy frequency-matching conditions, but designedly to inhibit RET by geometric configuration, the throughput of laser pulses can facilitate energy transfer processes that would otherwise be forbidden, by laser-assisted resonant energy transfer. Suitably configuring an arrangement of transition dipoles, it proves possible to design parallel planar arrays of optical donor and acceptor particles such that the transfer of energy from any single donor, to its counterpart in the opposing plane, can be switched by appropriate laser radiation. As the energy transfer is itself mediated electromagnetically, the device operates as an optical transistor. For simplicity, a pair of two-dimensional arrays is envisaged, each consisting of equally spaced, identical particles arranged on a square lattice. A detailed appraisal of the system, including a consideration of competing processes, suggests that this configuration offers a new basis for the design of optically activated nanoscale transistor arrays.

Energy migration between chromophores plays a prominent role in a range of energy harvesting assemblies. Recent advances in the design and production of light-harvesting polymers have led to the synthesis of novel two-photon absorbing dendrimers. To construct increasingly efficient multifunctional macromolecules of this type, understanding the inherent optical processes and disentangling them has become imperative. This paper explores the fundamental processes by means of which energy transfers from a donor chromophore to an acceptor through two-photon absorption from an input laser beam. It is determined that three distinct classes of mechanism can operate: (i) two-photon absorption by individual chromophores is followed by transfer of the energy to an acceptor group; (ii) a singly excited chromophore is excited to a virtual state by the additional absorption of a photon from the pump radiation field, coupled with resonance energy transfer to the acceptor, or; (iii) two-photon excitation of the acceptor results from acquisition of one quantum of energy from a singly excited neighbour group and another from the throughput radiation. These mechanisms may compete and, in certain cases, lead to manifestations of quantum interference. Generally, the most favoured mechanism is determined by a balance of factors and constraints. Principal amongst the latter are the choice of wavelength (connected with the possibility of exploiting certain electronic resonances, whilst judiciously avoiding others) and the precise chromophore architecture (taking account of geometric factors concerned with the relative orientation of transition moments). As the relative importance of each mechanism determines the key nanophotonic characteristics of the assembly, the principles and results reported here afford the means for expediting highly efficient two-photon energy migration.

Subwavelength metallic structures are used to design gratings with a great variety of transmittance levels. Such gratings can answer growing needs for complex transmittance devices, particularly useful for wave-front analysis applications. Having in mind the conception of a perfectly sinusoidal transmittance for the mid-infrared, we have decided to test the ability of subwavelength lamellar gratings to code the transmittance with several levels. In order to calibrate gratings transmission, as a function of the fill factor, we have designed, realized and measured samples made of six 2mm x 2mm gratings, with transmittance ranging from 10% to 95%. Experimental results for TM- and TE-polarized light are reported and analysed.

The knowledge of the near-field of extraordinary transmission through hole-arrays is mostly theoretical; there is less experimental validation of the theory. We study the near-field properties by measuring fluorescent molecules that are immersed in a solution and their Brownian motion. The measurements are performed by filling the space above the hole-array with fluorescent solution and exciting these molecules through the hole-array. By measuring both the fluorescence and the direct exciting light, it is possible to learn about the near-field properties.

Enhanced light transmission through metallic nanostructured films is considered. The response of nanometer annular apertures array in silver films are experimentally and theoretically investigated. The theory, the fabrication process and the experimental characterization are described. The calculations are based on a 3D Finite Difference Time Domain (FDTD) method. Concerning the experiments, optical far-field and near-field results are shown.

The holographic optical storage capacity with photopolymer is improved by creating a multigrating onto the surface of a azopolymer thin film with the use of a liquid droplet. We show by this method that three kinds of gratings can be created and controlled by different laser beam parameters as polarization or incident angle.

In this paper, we demonstrate the capability of the pulsed laser deposition techniques for designing the novel/new multifunctional materials which are usually unachievable by classical synthesis routes. It details about the sequential growth of various materials in form of superlattices by controlling them at nano-scale level in order to design the new structures with multifunctional properties. A discussion on the issues related with role of thickness of the oxides in designing the novel materials viz., multiferroics, together with how one can enhance the multifunctionality by controlling the size of the oxides at nano-level are presented. Also a brief comments on the issues related to the growth of the nano-oxides by pulsed laser deposition is discussed.

The fabrication of a rhenium containing hyperbranched polymer (1) and poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS) multilayer on different ZnO nanostructures, including free standing ZnO tetrapods and ZnO nanorod arrays using layer-by-layer approach was demonstrated. The growth of the multilayer film and the attachment of the metal nanoparticles on the ZnO surface were investigated by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The results show that accurate control in multilayer film growth can be achieved. This paper presents a versatile method in modifying the surface of different ZnO nanostructures.

Short microcavities consisting of two identical tapered hole mirrors etched into silicon-on-insulator ridge waveguides are investigated. They are designed for operating at telecom wavelength. We describe theoretically and experimentally two different ways to boost quality factors to some thousands. In one hand, we investigate the adaptation of mode profile to suppress mismatch losses. In an other hand, we explore the recycling of the losses. We obtained quality factor up to 3000, which opens the route to WDM applications.

By rapid thermal annealing the Ni film evaporated on thin SiO₂ layer covered Si substrate, we have successfully demonstrated the self-aggregation of two-dimensional randomized Ni nano-dots on Si wafer. The thin oxide layer prevents the formation of NiSi₂ compounds and facilitates the self-assembly of Ni nanodots from retaining the thermal power on SiO₂ layer. This greatly shrinks the annealing time required for metallic nanodot formation from >10 min to <30 sec. With the advantage of the self-assemble Ni/SiO₂ nano-dots based nano-mask, a large-area Si nano-pillar array with rod size of <50 nm can be formatted on Si substrate through the induced coupled plasma reactive ion etching (ICP-RIE) procedure. After removing Ni dots and the SiO₂ film on the Si substrate, both the visible and near infrared photoluminescence from the Si nano-pillar sample were observed and analyzed.

We study a set of low temperature (LT, 250°C) Stranski-Krastanow InAs/GaAs quantum dots (QDs) grown using molecular beam epitaxy (MBE). The QDs are studied by Photoluminescence (PL) and Time Resolved Differential Reflectivity (TRDR) for obtaining the carrier dynamics also. The LT-growth is expected to combine an ultrafast response time with a large QD optical nonlinearity, making it a good candidate for ultrafast all-optical switching devices. We observe a QD photoluminescence peak around 1200 nm on top of a background due to the As_Ga-V_As center. We observe that the PL-efficiency is quenched above 30K. The PL-efficiency increases by a factor of 45 - 280 as a function of excitation wavelength around the GaAs bandgap, for different samples. This points towards good optical quality QDs, which are embedded in an LT-GaAs barrier with high trapping efficiency. In the TRDR measurements, we observe an initial fast decay (80ps) followed by a much slower decay of about 800ps. The strong temperature dependence of the PL-signal is not observed in the reflectivity signal. This leads us to conclude that the electrons tunnel out of the QD and are subsequently efficiently trapped by As antisite defects while the hole decay dynamics take place at a slower rate, which is monitored in TRDR. Our observations point towards QDs with good optical quality, embedded in a LT-GaAs barrier in which the carriers are efficiently trapped at anti-site defects.