This PDF file contains the front matter associated with SPIE Proceedings Volume 10120, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

In the unfolding process a uniformly polarized optical vortex evolves into a complex polarization distribution within a birefringent crystal. In this paper we introduce the “unfolding region” to characterize this process. This is the real space region over which the polarization state travels half way around the Poincar´e sphere relative to that observed at the center of the beam. Ideally the region is a circle, but it can be distorted into an ellipse by a small tilt between the ordinary and extraordinary rays. We have applied the above analysis to an actual unfolding process observed with a birefringent interferometer.

We describe methods of Raman spectroscopy for resolving mono crystalline sucrose using vortex laser beam modes with circular polarization. Research up to this point has led to controversy as to whether beams carrying orbital angular momentum (OAM) are capable of interacting with chiral matter, but there is also a general lack of experimental or theoretical research into the interaction of vortex beams carrying OAM or vector beams with vibrational modes in matter. Our attempts to detect and measure interactions with sucrose in crystal form mediated by OAM have resulted in findings that indicate a worthy path for future inquiry.

Based on the Fraunhofer diffraction theory and the properties of dove prism, the coordinate relationships among the four spatial light modulator (SLM) sections in a vectorial optical field generator (VOF-Gen) are derived and experimentally verified. Taking the coordinate system of the first SLM section as reference, the coordinate displacements between the first SLM section and the subsequent ones are measured through employing the specially designed four-quadrant patterns with varying shifts of the corresponding cross point. Complex optical field could be accurately generated by combining the derived coordinate relationships and pre-compensation of the measured coordinate displacements. A typical complex optical field is generated and the experimental results demonstrate the validity of the proposed transverse alignment method for the VOF-Gen.

In the present presentation, we report the experimentally and theoretically investigated spatial wavefront conversion properties of an optical vortex (OV) generation system including azo-dye doped liquid crystal (ADDLC) polymer composite and vector beam illuminator, focusing on the abilities of flexibility and achromaticity. Threedimensional anisotropic structure was induced by recording vector beam in ADDLC and it can convert a polarized Gaussian beam into polarized OVs whose topological charge is depending on the structure of anisotropy. The photo-induced anisotropic structure can be re-initialized by turning it off and changing the illuminating polarization pattern of vector beam. Numerical simulations and experimental results showed that our anisotropic structure can generate OV with broadband spectrum.

It is widely known that beams that have optical vortices along the direction of propagation can be easily created in the laboratory. However, it is less well known that it is possible to create beams that have vortices transversely through the beam waist. Despite much work on beams with parabolic trajectories the creation of beams with transverse vortices are not well understood. Recently such beams have been created in the laboratory with computer-generated holograms. Though such beams can be created relatively easily, optimization of the vortex structure requires generation of the correct kinoform for the optical system. Imprecise application of such kinoforms can generate multiple vortices at the beam focus, which may not be optimal in many experimental applications. In this paper, we discuss the properties of such beams and investigate the optimal geometry for creating beams with transverse vortices. Applications for beams with transverse vortices may exist in optical micromanipulation, quantum communications and microscopy.

Photon sieves for generating and identifying beams with orbital angular momentum are presented. They are diffractive optical elements (DOEs) based on a traditional Fresnel zone plate (FZP), but composed of a series of microscopic pinholes usually centered on the bright zones. Each circular hole contributes to the focusing and there are multiple possibilities for applying pupil apodization to DOEs that are not possible, and/or difficult, and/or costly compared to optical systems with conventional lenses and mirrors. We will describe in detail the basic spiral photon sieve as well as how various types of the photon sieves can be combined into one optical element for spatial beam shaping.

Light with a complex amplitude structure has been successfully investigated in fundamental and applied optical sciences. Mature devices such phase modulating spatial light modulators (SLM) have allowed a myriad of experimental findings in classical as well as quantum optics. However, state transformations that are more complex than simple phase manipulation are still hard or even impossible to realize. We show that controlled scattering of structured light can be seen as a novel tool to achieve transformations, which haven’t been possible before. By adapting recently developed techniques to control a complex, random scattering process and using a feedback signal, we demonstrate for example how an appropriate phase front shaping can lead to a programmable, custom-tailored mode sorting. We are able to sort up to 7 different orbital angular momentum (OAM) modes with accuracies of up to 98% to arbitrarily chosen spots and verify the coherence between the sorted positions, an essential feature for future applications in quantum experiments. Additionally, we successfully demonstrate the sorting of more complex light modes, such as superpositions of OAM modes and different p-modes, modes with different radial structure, a task which was not demonstrated before. We also investigate the possibility to send structured light modes through otherwise opaque material and test multi-mode fibers as scattering devices to increase transformation efficiencies. Our findings can be seen as first step to use a controlled coherent scattering process as a novel tool for complex transformations of structured light.

We developed a method to extract information of 3-dimensional coherent fields using projective measurements. We are particularly interested in 3-dimensional fields that are produced by the intersection of two orthogonally polarized light beams. We find that for specific symmetric conditions we are able to deduce the 3-dimensional polarization ellipse of the every point in space.

We revisit the quantum weak measurement (QWM) by sketching the polarisation state dynamics on the Poincaré sphere and the associated geometric phase, which is considered the soul of QWM. Our experimental arrangement comprises a coherent laser beam as a source of pure state, two polarizers corresponding to pre- and post-selection and a tilted wave plate placed in-between them to introduce weak interaction. The pre-selected state is a linearly polarised beam that can be represented as a point on the Poincaré sphere equator and the weak interaction with the wave plate results in a small spread in S3 axis. Now, an orthogonal projection of this state leads two different geodesics on the surface of the sphere through its poles, starting from both sides of the spread to the orthogonal point. The post-selection is made by moving the projection point slightly away from the orthogonal position so that both geodesics shift to the equator which results in a rapid accumulation of geometric phase in the beam crosssection. A gradient in the linear momentum is developed as a consequence which gives amplified shift in the beam position.

Here we present different approaches to ultrafast pulse and polarization shaping, based on a “quantum fluid” platform of polaritons. Indeed we exploit the normal modes of two dimensional polariton fluids made of strong coupled quantum well excitons and microcavity photons, by rooting different polarization and topological states into their sub-picosecond Rabi oscillations. Coherent control of two resonant excitation pulses allows us to prepare the desired state of the polariton, taking benefit from its four-component features given by the combination of the two normal modes with the two degrees of polarization. An ultrafast imaging based on the digital off-axis holography technique is implemented to study the polariton complex wavefunction with time and space resolution. We show in order coherent control of the polariton state on the Bloch sphere, an ultrafast polarization sweeping of the Poincaré sphere, and the dynamical twist of full Poincaré states such as the skyrmion on the sphere itself. Finally, we realize a new kind of ultrafast swirling vortices by adding the angular momentum degree of freedom to the two-pulse scheme. These oscillating topology states are characterized by one or more inner phase singularities tubes which spirals around the axis of propagation. The mechanism is devised in the splitting of the vortex into the upper and lower polaritons, resulting in an oscillatory exchange of energy and angular momentum and in the emitted time and space structured photonic packets.

That a paraxial light beam with spin angular momentum (SAM,σ ) propagating in a helical trajectory leads to the appearance of Rytov-Vladimirsky-Berry (RVB) phase has been a topic of extensive research for the past several decades. Recently, using geometrical optics approximation, it was shown that variations in the beam propagation direction leads to generic parallel transport law – a beam with intrinsic orbital angular momentum (IOAM, l ) behaves topologically similar to polarized beam containing only SAM but of magnitude proportional to the total angular momentum TAM = l ± σ . By considering the interaction of a beam with IOAM, propagating in a non-planar trajectory and hence with extrinsic orbital angular momentum (EOAM), in an inhomogeneous medium we study the parallel transport of fiber mode structure as a manifestation of orbit-orbit interaction. The resulting rotation of the transverse beam structure due to the parallel transport of the LP fiber mode propagating along non-planar ray direction is attributed to the ‘orbital’ Berry phase. The mode transformation is simulated based on the interference of the vector-vortex modes excited in the TMF. The LP mode rotation angle calculated as a function of the beam position at the fiber input is expected to show topological features that can be mapped onto orbital Poincaré sphere.

In this paper an on-chip device capable of wavelength-selective generation of vortex beams is demonstrated. The device is realized by integrating a spiral phase-plate onto a MEMS tunable Fabry-Perot filter. This vortex-MEMS filter, being capable of functioning simultaneously in wavelength and orbital angular momentum (OAM) domains at around 1550 nm, is considered as a compact, robust and cost-effective solution for simultaneous OAM- and WDM optical communications. Experimental spectra for azimuthal orders 1, 2 and 3 show OAM state purity >92% across 30 nm wavelength range. A demonstration of multi-channel transmission is carried out as a proof of concept.

Shaping complex light fields such as nondiffracting beams, provide important novel routes to control laser materials processing. Nondiffracting beams are produced from an interference between waves with an angle kept constant along the propagation direction. These beams are of outmost importance for laser materials processing because they offer invariant light-matter interaction conditions. We have used and developed several families of beams generated with phase and amplitude shaping and we will review their impact for laser surface processing and high aspect ratio laser processing in the bulk of transparent materials. Bessel beams and higher order Bessel beams allow for high aspect ratio channel drilling, elongated void creation in the bulk of transparent media, or tubular damage creation. We will also discuss the impact of accelerating beam shaping, ie beams with a curved main intensity lobe, to dice materials with a curved edge. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 682032-PULSAR).

Snap-fits are classified as interlocking connections and commonly used to assemble two or more components in a fast and cost efficient way. The mechanism is simply based on mechanical flexibility. Therefore, the applications cover a broad field ranging from automotive engineering to mobile phone design. By scaling and transferring the snap-fit mechanism into micrometer scale, advantages can also be utilized to assemble complex microsystems. In this paper, a microsnap-fit based on a cantilever design is developed and investigated by means of optical techniques only. Two-photon polymerization as micro-stereolithography is utilized to manufacture the microcomponents and the mechanical flexibility is analyzed by optical forces in a holographic optical tweezer setup. The locking mechanism is theoretically and experimentally characterized, e.g, the flexibility of the polymer with regard to the design is studied. It can be demonstrated that assembling as well as disassembling of microcomponents is achievable. These findings provide fast and easy assembling of complex microsystems in the fields of microrobotics, -sensors, and -mechanics.

We will review recent work on nano and micro structured polymers, in particular liquid crystalline elastomers, such as to realise small, complex, structures that deform when exposed to light. The goal is to create artificial arms, and legs, walking and swimming artificial micro creatures, and photonic components, like micro resonators that adapt to their environment.

We investigate a force that has been predicted to discriminate molecules by their chirality when they are in the presence of an optical field with a polarization-helicity gradient. We investigate several experimental geometries for observing evidence of this force via enantiometer separation in racemic mixtures. We do this with singular-optical beams carrying a polarization helicity gradient across their transverse mode. Molecular diffusion and the dipole force – an intensity-gradient force – have so far precluded measurements of this force.

We present details on how the newly introduced technique of chiral rotational spectroscopy can be used to extract orientated information from otherwise freely rotating molecules in the gas phase. In this technique circularly polarized light is used to illuminate chiral molecules and shift their rotational levels to yield orientated chiroptical information via their rotational spectrum. This enables in particular the determination of the individual, physically relevant components of the orientated optical activity pseudotensor. Using the explicit example of (S)-propylene glycol we show how measuring the rotational spectrum of molecules in the microwave domain allows for the recording of a small set of rotational transitions from which the individual polarizability components can be determined.

We implement digital holograms for the creation and detection of the spatial modes of light. We make use of modal decomposition theory to determine the numerous properties of light, from the modal content of laser beams to decoding the information stored in optical fields carrying orbital angular momentum. We demonstrate the versatility of these techniques to characterize both structured and vector fields with static and propagating optical fields. Finally, we show a holographic technique to realise a communication link using a densely packed spatial mode set where we experimentally multiplex and de-multiplex over 100 spatial modes.

A laser cavity composed of a cylindrical mirror and a gain medium is used to generate scalar flower modes possessing orbital angular momentum. We proposed a new complex modes by using a hemi-cylindrical cavity or spatial light modulator to generate superposition of vector Laguerre-Gaussian modes and vector flower modes. The generated vector fields possessing not only orbital angular momentum but polarization properties which correspond to the specific point on a higher-order Poincaré sphere. This work paves the way to cavity laser in several applications.

Freely propagating light in the most general sense is governed by Maxwell’s equations as written in the strict absence of charge. These demand in particular that the electric and magnetic fields are divergenceless. The electromagnetic field lines must therefore extend indefinitely or else form closed loops. Solutions of the former kind, such as a single plane electromagnetic wave, are well-known. Various solutions of the second kind, such as an electromagnetic knot, are known as well, but the idea as a whole remains relatively unexplored. We will discuss these unusual electromagnetic disturbances, their creation, their dynamics and their potential applications. Our approach is centred upon the fact that any electromagnetic field must be expressible as a superposition of plane waves. If the field is monochromatic, the tips of the wavevectors of these waves must lie on the surface of a sphere in reciprocal space. Stable closed field line configurations can then be built by distributing these wavevectors in a suitably symmetrical manner whilst choosing their polarisations appropriately. Finally, solutions of this kind but with different frequencies can be added together to yield the most general form of freely 'propagating' electromagnetic disturbance. To produce such fields in practice at long wavelengths might require little more than suitable arrangements of antennas. At shorter wavelengths one may more usefully regard the solutions as being superpositions of various vector modes.

Array-specific propagation effects are relevant for evaluating cross-talk or coherent coupling in multichannel processing and designing complex interference maps. At pulse durations in few-cycle range, an important goal is to combine the flexibility of shaping structured beams with a high-quality temporal transfer. Therefore, low-dispersion actuator arrays have to be applied in a diffraction-free approach. Flexible structuring of sub-3-cycle Ti:sapphire laser pulse arrays was studied with collectively or individually tunable liquid crystal devices and thermally actuated mirrors. It is shown that the classical diffractive Talbot effect can be complemented by the spatio-temporal self-imaging of pulsed nondiffracting needle beam arrays.

We calculate transition amplitudes and cross sections for excitation of hydrogen like atoms by the twisted photon states, or photon states with large angular momentum projection on the direction of propagation. It is shown that when the transition rates are normalized to the local photon flux,the resulting cross sections for are singular near the optical vortex center [1], in close relation to the 'quantum core' concept introduced by Berry and Dennis. We also show that the photon state develops polarization singularity in the beam center due to circular dichroism of the photon absorption by atoms via higher multipoles. [1]. A. Afanasev, C.E. Carlson, and A. Mukherjee, High-multipole excitations of hydrogen-like atoms by twisted photons near a phase singularity, Journal of Optics 18, 074013 (2016)

Optical communications has historically experienced capacity growth by multiplexing many channels, and space-division-multiplexing (SDM) appears to be the next domain to exploit. SDM can encompass multiple spatially overlapping “orthogonal” modes to achieve mode-division-multiplexing (MDM). Key advantages of modal orthogonality are the ability to efficiently (de)multiplex independent data streams and co-propagate them, all with little inherent crosstalk. An MDM approach using orbital angular momentum (OAM) has emerged as a potential method to efficiently multiplex many spatially over-lapping data-carrying beams. This presentation will highlight transmission of multiple OAM beams as well as the various technical challenges in realizing such a system.

Emerged as the quantum counterpart of classical random walks, quantum walks are established precious resources in a variety of quantum sciences. Recent studies have shown that quantum walks may be characterized by topological invariants, in close analogy to condensed matter systems exhibiting topological order. Exploiting these features, quantum walks are currently used to simulate topological systems and to probe their exotic features. Here we present the implementation of a one-dimensional quantum walk protocol based on the orbital angular momentum of light, manifesting the topological phases that characterize time-periodic systems (Floquet topological insulators) showing chiral symmetry. By considering the orbital angular momentum spectrum of a light beam undergoing this quantum evolution, we show that the associated statistical moments have marked differences in distinct phases and contain information on the system topology. While varying a control parameter determining the value of the invariants, these moments in the large step-number limit exhibit a sharp variation at the phase changes. We show that these phenomena arise from the singular behavior of the dispersion relation at the transition points. The extension of our results to systems featuring different symmetries, or characterized by higher spatial dimensions, may unveil novel intriguing features associated with these complex systems.

Across various areas in the optical world, there has been a growing interest in exploiting the properties of non-separable optical fields. A class of non-separable fields, known as vector modes, exhibit a coupling between the spatial and polarisation degrees of freedom that is akin of entanglement in quantum mechanics. These vector modes, however, are typically characterized using qualitative measurements which are inadequate in determining to what extent an optical field is non-separable. Here, we present tools to characterize the degree of non-separability of an arbitrary optical field, exploiting the similarities between vector modes and quantum entangled states. As an example, we use vector modes carrying orbital angular momentum to demonstrate the effectiveness of our scheme, and note that the approach can be generalized to vector modes as a whole.

High-dimensional encoding using higher degrees of freedom has become topical in quantum communication protocols. When taking advantage of entanglement correlations, the state space can be made even larger. Here, we exploit the entanglement between two dimensional space and polarization qubits, to realize a four-dimensional quantum key distribution protocol. This is achieved by using entangled states as a basis, analogous to the Bell basis, rather than typically encoding information on individual qubits. The encoding and decoding in the required complementary bases is achieved by manipulating the Pancharatnam-Berry phase with a single optical element: a q-plate. Our scheme shows a transmission fidelity of 0.98 and secret key rate of 0.9 bits per photon. While the use of only static elements is preferable, we show that the low secret key rate is a consequence of the filter based detection of the modes, rather than our choice of encoding modes.

Dexterous contactless manipulation of microscopic matter in three dimensions is possible since the development of optical tweezers. This scheme using a single laser beam can handle particles with forces in the piconewton range with subnanometer resolution. Although various acoustical traps, mainly using standing wave fields, have been proposed over the last 50 years, several difficulties have prevented the demonstration of acoustical tweezers using a single beam of ultrasound. Deriving the analytical expression for the acoustic radiation force applied on an elastic sphere, the feasibility and the experimental demonstration of the trapping of small elastic particles with a single ultrasonic beam in three dimensions was recently achieved. These acoustical tweezers upscale by several orders of magnitude the range of forces and particle sizes available in the realm of contactless manipulation.

Full control of the dark ray structure of an optical beam requires an adequate mathematical framework to describe its properties. In this presentation we will provide a new set of mathematical tools whose ultimate goal is to complete a full mathematical representation of dark ray optics. Using this mathematical representation we will discuss the different possibilities to achieve full control of the dark rays trajectories using standard optical elements in an analogous way to the manipulation of ordinary bright rays in geometrical optics.

The Babinet’s principle is a general theorem that holds for electromagnetic waves and is often applied to diffraction of light. Diffraction pattern of a body and that of the complement body are compared and the sum of both radiation patterns must be the same as for an unobstructed beam. In most cases of practical applications light fields are measured by recording the intensity and is limited by a numerical aperture smaller than one. In our contribution we study amplitude and phase behind amplitude structures. We demonstrate using the example of Talbot images what happens in experiments that try to use the Babinet’s principle to understand diffraction patterns for small periodic structures. Of particular interest is the regime close to the structure, the so-called Fresnel diffraction regime. We present results of simulation and measurement to show the impact of a limited numerical aperture

We investigate disclinations in the orientation of space-variant polarization patterns produced by collinear non-factorizable superpositions of high-order spatial modes and polarization. Asymmetric disclination patterns were formed by superpositions of spatial modes with asymmetric optical vortices. They give rise to monstar patterns of high order that can have a negative or positive disclination index. This has led to an examination of what constitutes a monstar. We present theoretical as well as experimental results.

Widespread use of optical manipulation in combination with advanced imaging techniques will be accelerated by compact, optically simple approaches which are readily integrated into advanced microscopy platforms. For example, optical manipulation has been combined with confocal, multi-photon, and STED microscopes. However, these typically require addition of optical components into the existing beam paths of the microscope, increasing complexity and potentially compromising image quality. Optical fiber trapping (OFT) offers an ultra-compact and simple solution but compromises on trap quality due to the low numerical aperture (NA) and short manipulation distance of optical fibers. Tapered fibers can be fabricated but this further reduces the manipulation distance and requires access to specialist fabrication facilities. Here we present a compact, single-beam, high NA OFT probe design based on a graded-index (GRIN) micro-objective lens and single-mode fiber. The OFT probe uses only off-the-shelf components, enables optical trapping at a distance of 200μm from the probe tip, and is compatible with inverted imaging systems. A challenge with specialist imaging systems is the incompatibility between the specialist imaging modality of the platform and the imaging modality required for trap characterization, resulting in noisy and poor trap characterisation data. To overcome this challenge, we developed an adaptive image filter based on principal component analysis (PCA). The filter separates orthogonal degrees of motion in trap characterisation movies and strong stochastic noise can be removed before tracking, resulting in accurate characterisation. We demonstrate the use of this PCA image filter for in situ characterisation of the GRIN lens OFT probe.

Configurable trapping potentials are of great interest in cold atom physics, as they enable production of dynamical highly flexible fields that exhibit unprecedented stability and diverse geometries. Direct imaging can be used to create large area trapping potentials but is often overlooked due to its inability to correct for wavefront aberrations of the optical system [1]. This need not be a major disadvantage for a well-corrected optical system and brings advantages including the simplicity and speed of direct imaging. This is in contrast to the Fourier plane method which requires complex calculations to generate proper holograms and suffers from phase defects and speckle. For applications in cold atom trapping, these effects are especially detrimental as the atoms are sensitive to perturbations at the ~1% level of the optical potential. Our approach uses off-the-shelf lenses and microscope objectives and is able to achieve 630(10) nm full width half maximum (FWHM) patterning resolution using a 0.45 NA objective, within 5% of the diffraction limit of the system, while imaging through 1.25 mm of glass. The light field patterning is done using a digital micromirror device (DMD) which allows for dynamic trapping potentials due to its ability to store 13,889 frames and its 22 kHz full frame refresh rate. We use this method to pattern planar potentials for the purpose of cold atom experiments and have found that for atoms, which tend to respond relatively slowly to perturbations, it is possible to combine half-toning and time averaging to produce grey scale patterns, additionally allowing for pattern correction [2]. [1] P. C. Mogensen and J. Glückstad, Optics Communications 175, 75–81 (2000). [2] G. Gauthier, I. Lenton, N. McKay Parry, M. Baker, M. J. Davis, H. Rubinsztein-Dunlop, and T. W. Neely, arXiv preprint arXiv:1605.04928 (2016).

Recently, it was predicted that the energy transfer between normal modes of open systems with a specific type of degeneracy known as an exceptional point (EP) could be achieved by topological operations, and that the outcome of these operations would be non-reciprocal.¹ Here we demonstrate this topological transfer of energy between two vibrational modes of a cryogenic optomechanical device using a tunable laser. We also show the non-reciprocity of the energy transfer process. These results open up new directions in system control, as well as other dynamical processes of multimode systems that are robust against small perturbations.

Raman spectroscopy can provide useful chemical information of nanostructures and molecules. We combine Raman spectroscopy with atomic force microscopy, through dual color photo-induced force microscopy (PiFM). In this modality, images with Raman contrast can be generated with a spatial resolution well below 10 nm at ambient temperature and pressure. Here we utilize this technique to visualize molecules on surfaces with high spatial and temporal resolution. Compared to previous Raman sensitive PiFM measurements, we employ femtosecond pulses and show that this technique is highly sensitive to the stimulated Raman scattering interaction in the molecule.

We propose to use optical tweezers to probe the Casimir interaction between micro-spheres inside a liquid medium for geometric aspect ratios far beyond the validity of the widely employed proximity force approximation. This setup has the potential for revealing unprecedented features associated to the non-trivial role of the spherical curvatures. For a proof of concept, we measure femtonewton double-layer forces between polystyrene microspheres at distances above 400 nm by employing very soft optical tweezers, with stiffness of the order of fractions of a fN/nm. As a future application, we propose to tune the Casimir interaction between a metallic and a polystyrene microsphere in saline solution from attraction to repulsion by varying the salt concentration. With those materials, the screened Casimir interaction may have a larger magnitude than the unscreened one.

Trapping nanoscopic objects to observe their dynamic behaviour for extended periods of time is an ongoing quest. Particularly, sub-100nm transparent objects are hard to catch and most techniques rely on immobilisation or transient diffusion through a confocal laser focus. We present an Anti-Brownian ELectrokinetic trap^1–7 (pioneered by A. E. Cohen and W. E. Moerner) to hold nanoparticles and individual F_oF₁-ATP synthase proteins in solution. We are interested in the conformational dynamics of this membrane-bound rotary motor protein that we monitor using single-molecule FRET. The ABELtrap is an active feedback system cancelling the nano-object’s Brownian motion by applying an electric field. We show how the induced electrokinetic forces confine the motion of nanoparticles and proteoliposomes to the centre of the trap.

Early detection of diseases can save lives. Hence, there is emphasis in sorting rare disease-indicating cells within small dilute quantities such as in the confines of lab-on-a-chip devices. However, before diseased cells can be studied in isolation, it is necessary to identify them against normal healthy cells. With the richness of visual information, a lot of microscopy techniques have been developed and have been crucial in biological studies. To utilize their complementary advantages we adopt both fluorescence and brightfield imaging in our optical cell sorter. Brightfield imaging has the advantage of being non-invasive, thus maintaining cell viability. Fluorescence imaging, on the other hand, takes advantages of the chemical specificity of fluorescence markers and can validate machine vision results from brightfield images. Visually identified cells are sorted using optical manipulation techniques. Scattering forces from beams actuated via efficient phase-only efficient modulation has been adopted. This has lowered the required power for sorting cells to a tenth of our previous approach, and also makes the cell sorter safer for use in clinical settings. With the versatility of dynamically programmable phase spatial light modulators, a plurality of light shaping techniques, including hybrid approaches, can be utilized in cell sorting.

We present for the first time a wavelength tunable fiber-based optical tweezer using a graded index multimode optical fiber (GIMF). Optical fiber tweezer is a viable replacement for the bulky objective-based tweezers because of the low-cost and user-friendly operation and maneuverability. The proposed optical fiber tweezer consists of a GIMF spliced to a single mode fiber into which a wavelength tunable laser is launched. The exit field at the end-facet of the GIMF is used for tweezing. The GIMF setup is capable of generating a tunable-distance optical trap over a hundred microns by just tuning the laser wavelength. The position of the optical trap can also be customized with the proper design of the GIMF and straining the fiber. The length of the GIMF also plays an important role in the operation of the device. This length needs to be fined-tuned only over less than 500 microns due to the self-imaging properties of the beam propagating in a GIMF; therefore, the necessary length adjustments can be easily done by polishing the end-facet of the fiber. The numerical results also show that as the optical trap moves farther away from the GIMF tip, the optical trap gets weaker. The results also show that the minimum input power to meet the stability conditions for a particle with a radius of 0.1 micron is around 400 mW.

Recently we proposed the concept of so-called Light Robotics including the new and disruptive 3D-fabricated micro-tools coined Wave-guided Optical Waveguides that can be real-time optically manipulated and remote-controlled with a joystick in a volume with six-degrees-of-freedom. Exploring the full potential of this new ‘drone-like’ light-driven micro-robotics in challenging microscopic geometries requires a versatile and real-time reconfigurable light addressing that can dynamically track a plurality of tiny micro-robots in 3D to ensure continuous optimal light coupling on the fly. Our latest developments in this new and exciting research area will be reviewed.

Transmittance of Laguerre-Gaussian (LG) vortex beams in mouse brain tissue is measured with different orbital angular momentums (OAM). The transition point from ballistic to diffusive region for the mouse brain tissue is determined at about 480 μm. The observed transmittances of the LG beams show independence on OAM modes in both ballistic and diffusive regions, which may be attributed to the interference effects from brain tissue.

We discuss null knotted solutions to Maxwell's equations, their creation through Bateman's construction, and their relation to the Hopf-fibration. These solutions have well-known, conserved properties, related to their winding numbers. For example: energy; momentum; angular momentum; and helicity. The current research has focused on Lipkin's zilches, a set of little-known, conserved quantities within electromagnetic theory that has been explored mathematically, but over which there is still considerable debate regarding physical interpretation. The aim of this work is to contribute to the discussion of these knotted solutions of Maxwell's equations by examining the relation between the knots, the zilches, and their symmetries through Noether's theorem. We show that the zilches demonstrate either linear or more complicated relations to the p-q winding numbers of torus knots, and can be written in terms of the total energy of the electromagnetic field. As part of this work, a systematic multipole expansion of the vector potential of the knotted solutions is being carried out.