This PDF file contains the front matter associated with SPIE Proceedings Volume 8274, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

A spinning medium is predicted to induce a slight rotation in a transmitted image. We amplify this effect by use of ruby as a slow light medium, giving image rotations of several degrees. In terms of the orbital angular momentum such rotations are analogous to the mechanical Faraday effect.

The interaction of light's orbital angular momentum (OAM) with matter has still several unexplored aspects. In particular, it is unknown if there exists for OAM an effect analogous to spin angular momentum-based optical activity. Here we study experimentally the influence of OAM on the interaction of light with a cholesteric liquid crystal polymer. We use strongly focussed light where the polarization and the orbital degrees of freedom are coupled. Two possible manifestations of an OAM-sensitive interaction are investigated: (i) the modification of circular dichroism, and (ii) the occurrence of intermodal dispersion of the {l = +1, l = -1} modes. We conclude that such an interaction does not exist within the experimental parameter range studied here.

The recent interest in "superchiral" fields, generated near planar chiral metamaterials, has prompted questions of deeper links between beam helicity and optical angular momentum. To address the issues invites consideration of the most appropriate metrics and their physical interpretation. This paper develops the photonic attributes of the chirality density, one of several measures that are conserved quantities for a vacuum electromagnetic field. The chirality density is explored with reference to an arbitrary polarization basis, and related to optical angular momentum. Analyzing multimode beams with complex wavefront structures affords a deeper understanding of the interplay between optical chirality and angular momentum.

In this report we theoretically calculate and experimentally measure the OAM density of a coherent superposition of both symmetric and non-symmetric non-diffracting Bessel beams. Although the intensity pattern of the superimposed field rotates at a fixed angular velocity (which is due to the differing wave-vectors of the component fields), we show that the magnitude and direction of the OAM is dependent on the radial position within the field. We outline a simple approach using only a spatial light modulator to measure the OAM density for a superposition of non-diffracting Bessel beams. Our quantitative measurements are in good agreement with predicted values.

A recently proposed higher order Poincare sphere constructed from the total optical angular momentum eigenstates of circular polarized optical vortices and the higher order states of polarization of vector vortex beams is presented. This novel representation can be applied to facilitate the description of various vector polarization beams such as radial and azimuthally polarized cylindrical vector beams, as well as the spin orbit conversion of q-plates. An experimental method with which to measure higher order Stokes parameters in terms of a spin and orbital decomposition of a light beam is also discussed.

Recently, we presented an experimental realization of a deterministic optical rocking ratchet [Arzola, A. V., et al. Phys Rev. Lett. 106: 168104 (2011)]. We obtained a systematic motion of microparticles and demonstrated that it is possible to control their average velocity and their direction of motion in real time by properly tuning experimental parameters. We have extended our study in order to establish the conditions for observing the crucial effect of current reversals in deterministic conditions, phenomenon predicted more than a decade ago, but experimentally demonstrated for the first time in our system.

We have built a compact light source for bright squeezed twin-beams at 795nm based on four-wave-mixing in atomic ⁸⁵Rb vapor. With a total optical power of 400mW derived from a free running diode laser and a tapered amplifier to pump the four-wave-mixing process, we achieve 2.1 dB intensity difference squeezing of the twin beams below the standard quantum limit, without accounting for losses. Squeezed twin beams generated by the type of source presented here could be used as reference for the precise calibration of photodetectors. Transferring the quantum correlations from the light to atoms in order to generate correlated atom beams is another interesting prospect. In this work we investigate the dispersion that is generated by the employed fourwave- mixing process with respect to bandwidth and dependence on probe detuning. We are currently using this squeezed light source to test the transfer of spatial information and quantum correlations through media of anomalous dispersion.

We have developed a new approach to measuring the spatial position of a single photon. Using fibers of different length, all connected to a single detector allows us to use the high timing precision of single photon avalanche diodes (SPAD) to spatially locate the photon. We have built two 8-element detector arrays to measure the full-field quantum correlations in position, momentum and intermediate bases for photon pairs produced in parametric down conversion. The strength of the position-momentum correlations is found to be an order of magnitude below the classical limit.

High-dimensional entangled photons pairs are interesting for quantum information and cryptography: Compared to the well-known 2D polarization case, the stronger non-local quantum correlations could improve noise resistance or security, and the larger amount of information per photon increases the available bandwidth. One implementation is to use entanglement in the spatial degree of freedom of twin photons created by spontaneous parametric down-conversion, which is equivalent to orbital angular momentum entanglement, this has been proven to be an excellent model system. The use of optical fiber technology for distribution of such photons has only very recently been practically demonstrated and is of fundamental and applied interest. It poses a big challenge compared to the established time and frequency domain methods: For spatially entangled photons, fiber transport requires the use of multimode fibers, and mode coupling and intermodal dispersion therein must be minimized not to destroy the spatial quantum correlations. We demonstrate that these shortcomings of conventional multimode fibers can be overcome by using a hollow-core photonic crystal fiber, which follows the paradigm to mimic free-space transport as good as possible, and are able to confirm entanglement of the fiber-transported photons. Fiber transport of spatially entangled photons is largely unexplored yet, therefore we discuss the main complications, the interplay of intermodal dispersion and mode mixing, the influence of external stress and core deformations, and consider the pros and cons of various fiber types.

This article presents a proposal for preparing photon pairs in states that are entangled in their spatial modes. The method allows the encoding of any pair of spatial modes that is desired, without restrictions; a procedure that up to now has been elusive. This method consists of three steps: preparing photon pairs in polarization-entangled states, filtering the spatial mode, and use of polarization interferometers with diffractive mode-encoding elements to effect entanglement swapping between polarization and spatial modes. An extension of the method consists of entangling polarization and spatial mode, allowing the preparation of a 4-qubit cluster state of two photons.

We explore the optical flux lattices produced for ultra-cold atoms in the radiation field when both the atom-light coupling and the detuning exhibit an oscillatory behavior. We analyze not only the magnetic flux but also the geometric vector potential generating the flux, as well as the accompanying geometric scalar potential. We show how to deal with the gauge-dependent singularities of the Aharonov-Bohm (AB) type appearing in the vector potentials for the optical flux lattices. We present a way to calculate the continuous magnetic flux through the elementary cell via the singularities of the vector potential inside the cell. The analysis is illustrated with a square optical flux lattice. We present a way of creating such a lattice using the Raman transitions induced by a set of properly chosen polarization-dependent standing waves propagating at a right angle and containing a time-phase difference.

We decompose the light field in the focal plane of an imaging system into a set of optical eigenmodes. Subsequently, the superposition of these eigenmodes is identified, that optimizes certain aspects of the imaging process. In practice, the optical eigenmodes modes are implemented using a liquid crystal spatial light modulator. The optical eigenmodes of a system can be determined fully experimentally, taking aberrations into account. Alternatively, theoretically determined modes can be encoded on an aberration corrected spatial light modulator. Both methods are shown to be feasible for applications. To achieve subdiffractive light focussing, optical eigenmodes are superimposed to minimize the width of the focal spot within a small region of interest. In conjunction with a confocal-like detection process, these spots can be utilized for laser scanning imaging. With optical eigenmode engineered spots we demonstrate enhanced two-point resolution compared to the diffraction limited focus and a Bessel beam. Furthermore, using a first order ghost imaging technique, optical eigenmodes can be used for phase sensitive indirect imaging. Numerically we show the phase sensitivity by projecting optical eigenmodes onto a Laguerre-Gaussian target with a unit vortex charge. Experimentally the method is verified by indirect imaging of a transmissive sample.

The cell-BOCS is a novel microfluidics based cell-sorting instrument utilizing next generation optical trapping technology developed at the Technical University of Denmark. It is targeted emerging bio-medical research and diagnostics markets where it for certain applications offers a number of advantages over conventional fluorescence activated cell-sorting (FACS^TM) technology. Advantages include gentle handling of cells, sterile sorting, easy operation, small footprint and lower cost allowing out-of-core-facility use. Application examples are found within sorting of fragile transfected cells, high value samples and primary cell lines, where traditional FACS technology has limited application due to it's droplet-based approach to cell-sorting. In the diagnostics field, in particular applying the cell-BOCS for isolating pure populations of circulating tumor cells is an area that has generated a lot of interest.

We present laser trapping behavior of individual smectic 4'-n-pentyl-4-cyanobiphenyl liquid crystalline micro-droplet dispersed in heavy water; in particular, laser trapping-induced molecular reconfiguration of the optically trapped droplet when the laser trapping power is above a definite threshold. The reconfiguration undergoes throughout the inside of the droplets even though their size is larger than the focal spot, and the threshold laser power depends on the droplet size. We propose that the reconfiguration mechanism involves optical reorientation at the focal volume competing with the droplet-liquid interfacial anchoring effect, leading to symmetry breaking throughout the inside of the optically confined droplet. With this mechanism, we qualitatively described the existence of the threshold power and the dependence of the threshold upon the droplet size.

We develop an active cell sorter that utilizes machine vision for cell identification. Particles are identified based on visual features such as shape, size and color using image processing. The sorter shares features from our previously developed BioPhotonics Workstation. Hence, it benefits from the extended axial manipulation range provided by the low numerical aperture geometry. Detected particles are catapulted axially by several hundred microns, allowing them to be moved from one laminar flow region to another. As the sorting motion is transverse to the viewing plane, multiple particles can be catapulted at the same time, therefore enabling parallel sorting. The sorter is developed with a minimal footprint such that it can operate as a table top device, an advantage over flow cytometry or FACS systems.

We report on the investigation of crossed-Bessel-beam and hybrid Bessel-Gauss configurations for optical trapping of microscopic particles. The non-diffractive nature of the Bessel beam removes the need for high-NA optics. Crossed beam configurations allow creating trapping volumes with small aspect ratio, in comparison to single-beam Bessel traps that create wave-guide like structures. We present numerical simulations of said geometries and present experimental data of in-situ Bessel beam forces on polystyrene beads as precursor to the realization of a random access Bessel trap.

Microscopic structuring and organization of matter utilizing optically induced forces has a high potential to enable novel material properties and photonic features. We briefly review two promising classes of light fields that combine a high degree of order with exciting propagation properties, and demonstrate applications in optical micromanipulation and the creation of refractive index gratings in photorefractive materials. While the class of nondiffracting beams allows for axially extended optical potential landscapes and corresponding structuring of the refractive index, the class of selfsimilar beams offers continuous diffraction during propagation that can be exploited for two- and three-dimensional optical organization. We demonstrate how the transverse organization of the structured light fields can be transferred to corresponding structuring of bulk material and colloidal systems.

Fine complex light structure, optical singularities and electroconductivty of nematic 5CB doped by multi-walled carbon nanotubes (MWCNTs) were investigated. MWCNTs gather spontaneously to system of micro scale clusters with random fractal borders at small enough concentration. They are surrounded by the striped micro scale cladding which creates optical singularities in propagating laser beam. Applied transverse electric field above the Freedericksz initiates homeotropic arrangement of 5CB and the striped inversion walls between nanotubes clusters what diminishes free energy of a composite. Theory of their appearance and properties was built. Simultaneously the striped cladding disappears what can be treated as new mechanism of structure orientation nonlinearity in nonlinear photonics. Polarization singularities (circular C points) were measured firstly. Percolation of clusters enhances strongly electrical conductivity of the system and creates inversion walls even without applied field. Carbon nanotubes composites in LC form bridge between nano dopants and micro/macro system and are promising for applications. Elaborated protocol of singular optics inspection and characterization of LC nanocomposites is promising tool for applications in modern nanosience and technique.

We present optical vortex beams interaction via degenerate two-wave mixing in liquid crystal light-valve, LCLV. The LCLV is made by combining a transparent photosensitive substrate with a nematic liquid crystal and displays a large Kerr-like effect. Being characterized by a large transverse size and spatial homogeneity, the LCLV allows performing nonlinear mixing experiments with several vortex beams and testing the interaction of different topological charges. We show that the wave-mixing occurring in the LCLV leads to the exchange of topological charge between vortex and to a cascaded generation of vortex beams. A mean-field model is developed and is shown to account for the charge selection rules observed after the mixing process. Fractional charges are demonstrated to participate to the wave-mixing in a robust way, following the same charge selection rules as for integer charges.

We report on the generation of photonic nanojets, which resemble optical bottle beams. They are realized by manipulating the illumination of dielectric microspheres. As illumination we use the outer region of deliberately truncated Bessel-Gauss beam or a focused Gaussian beam with intentionally induced spherical aberrations. For the Bessel-Gauss beam possessing a single side lobe only, the nanojet spot resembles an optical bottle beam with a strong confinement due to the nanojet effect. When multiple side lobes of the aberrated focal spot are used, a chain of 3D optical bottle beams appears. We show the 3D intensity distributions close to the spot and discuss the main characteristics of such optical bottle beams.

Interactions between femtosecond solitons in a nonlinear photonic-crystal fiber are of fundamental interest. But many practical applications would abound if solitons could be arbitrarily superposed into multiples in the fiber. Here, we numerically and experimentally demonstrate a first step towards this aim, the creation of a soliton pair with arbitrary relative phase, delay, and frequency throughout almost the entire output parameter space with the aid of a pre-shaped fiber input field.

Dynamics of polarization optical singularities chain reactions in generic elliptically polarized speckle fields created in photorefractive crystal LiNbO3 was investigated in details Induced speckle field develops in the tens of minutes scale due to photorefractive 'optical damage effect' induced by incident beam of He-Ne laser. It was shown that polarization singularities develop through topological chain reactions of developing speckle fields driven by photorefractive nonlinearities induced by incident laser beam. All optical singularities (C points, optical vortices, optical diabolos,) are defined by instantaneous topological structure of the output wavefront and are tangled by singular optics lows. Therefore, they have develop in tangled way by six topological chain reactions driven by nonlinear processes in used nonlinear medium (photorefractive LiNbO3:Fe in our case): C-points and optical diabolos for right (left) polarized components domains with orthogonally left (right) polarized optical vortices underlying them. All elements of chain reactions consist from loop and chain links when nucleated singularities annihilated directly or with alien singularities in 1:9 ratio. The topological reason of statistics was established by low probability of far enough separation of born singularities pair from existing neighbor singularities during loop trajectories. Topology of developing speckle field was measured and analyzed by dynamic stokes polarimetry with few seconds' resolution. The hierarchy of singularities govern scenario of tangled chain reactions was defined. The useful space-time data about peculiarities of optical damage evolution were obtained from existence and parameters of 'islands of stability' in developing speckle fields.

This article presents a study of Poincare-mode patterns produced by superpositions of high-order Laguerre-Gauss modes in orthogonal polarization eigenstates. We cover the cases of three polarization bases: circular, linear and elliptical. We show that a variety of patterns can be created, many containing polarization singularities and multiple mappings of the Poincaré sphere onto the beam mode.

Localized near field on a nanostructure has been attracting much attention for a template for size-selective optical trapping beyond the diffraction limit. The near-field optical trapping has mainly been studied by using metallic substrates such as Au nanodot pairs, periodic Al nanoslits, and nanoapertures in an Au film. In this paper, we newly design a Miescattered near-field optical trapping scheme for size-selective photocatalysis by using pairs of poly-rutile TiO₂ nanospheres. The optical intensity distribution in a gap between the nanospheres was simulated by a FDTD (Finite- Difference Time-Domain) method. The simulation system consists of two nanospheres of 240 nm in diameter placed on a silica substrate in water. The 400 nm excitation laser is used for both the near-field generation and the photocatalyst pumping. The optical force for the trapping was calculated based on the near-field intensity distribution. The results suggest that the optical force generated by the proposed system is sufficient for near-field optical trapping which provides size-selective photocatalysis for killing virus, etc.

We developed a Matlab based procedure for tracking phase singularities in optical fields. It visualises the motion of the singularities and quantifies their charges while the wave field propagates. We will explain how this procedure works and present some singularity trajectories calculated by this method. It will turn out that this procedure might be very useful for investigating the behaviour of phase singularities.

The first experimental evidence of speckle instability is realized by using a liquid crystal cell with a photosensitive wall. The light is transversally scattered in the liquid crystal cell, where a two-dimensional controlled disorder is imprinted through suitable illuminations of the photoconductive wall and the nonlinearity is obtained through optical reorientation of the liquid crystal molecules. Above a critical threshold of the input intensity, the speckle pattern starts spontaneously to oscillate with a characteristic frequency related to the response time of the nonlinear medium. Moreover, the oscillation threshold depends on the scattering mean free path, thus, confirming the crucial role played by disorder in inducing the instability.

We previously developed an achromatic method for the generation of the white-light optical and polarization vortices using axially-symmetric polarizer (ASP). In the present presentation, we report the experimental study on the Fresnel diffraction characteristics of the vortices generated by ASP. The diffraction pattern of the optical vortex has a dark core whose diameter is not scaled by the beam diameter. This behavior is described by the numerical simulation for a point-like vortex at ASP. We also studied the polarization change of a radially polarized light from ASP owing to the diffraction. This change can be explained by the decomposition of the radially polarized light into a plane wave and a point-like optical vortex which are respectively circularly-polarized with opposite handedness.

We introduce two high efficiency thin-film optical elements, operating over a wide spectral range, to generate and control the Orbital Angular Momentum (OAM) of various light sources: a broadband q-plate and a broadband Forked Polarization Grating (FPG). The broadband OAM manipulation is achieved by thin liquid crystal polymer layers that are aligned to provide the required spatially varying anisotropy. These elements operate using geometric phase principles to generate raised and lowered OAM modes whose efficiencies are sensitive to the polarization state of the incident light. We discuss the design principles involved and experimentally demonstrate broadband q-plates and FPGs that are highly efficient (> 90%) in the visible wavelength range. These thin film elements enable easy integration into various optical systems requiring broadband OAM manipulation such as optical trapping and high capacity information.