This PDF file contains the front matter associated with SPIE Proceedings Volume 7950, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We give an exact self-consistent operator description of the spin and orbital angular momenta, position, and spin-orbit interactions of nonparaxial light in free space. We apply the general theory to symmetric and asymmetric Bessel beams exhibiting spin- and orbital-dependent intensity profiles. The exact wave solutions are clearly interpreted in terms of the Berry phases, quantization of caustics, and Hall effects of light, which can be readily observed experimentally.

Orbital angular momentum (OAM) entangled bi-photons are a resource for the higher dimensional implementation of quantum cryptography, which allows secure communication over various channels. In the case where free-space is used as communication channel the initial OAM entangled bi-photon loses some or even all of its entanglement because of the scintillation that it experiences while propagating through the turbulence in the atmosphere. This decoherence of OAM entanglement has so far only been studied for the case of weak turbulence. Unfortunately, it is the more challenging strong turbulence scenario that is relevant for the practical implementation of free-space quantum communication through the atmosphere. Using an approach that differs from previous approaches, we derive a master equation for the evolution of an OAM entangled bi-photon during propagation through turbulence. However, in our approach the equation contains a derivative with respect to the propagation distance instead of time. The principle is to consider the propagation over an infinitesimal distance of OAM basis states through a random medium. This approach allows one to include, not only the effect of turbulence of arbitrary strength, but also the effect of the inner and outer scale of the turbulence, as represented by the Tartarskii and von Karman spectra. The resulting expression can predict the rates of decoherence for arbitrary initial OAM entangled states and can be used to calculate the concurrence, which measures the amount of entanglement, as a function of propagation distance for different initial entangled OAM states.

We report development of a two-photon polymerization (TPP) microscope, for micro-fabrication of microstructures, which is capable of optical manipulation by use of optical tweezers. The system is based on an inverted Nikon microscope with a tunable Ti: Sapphire femto-second (fs) laser coupled to the upper back port. While in modelocked condition, nanoparticles and wires were fabricated in photo-polymerizable synthetic materials using TPP. By axial positioning of the focused TPP laser beam, 1D-structures (for use as wave guide) were fabricated at desired height above the surface of the substrate. In the mode lock-OFF condition the same tunable laser microbeam was employed as optical tweezers to the hold the nanostructures and manipulate them even in highly viscous medium before immobilizing. Size of the TPP induced structure was found to depend on the fs laser intensity and exposure. Further, by shaping the fs laser beam to line pattern, linear 1D structures could be fabricated without scanning the beam or stage, which remain aligned along the line intensity profile due to anisotropic trapping force of the line tweezers in X and Y-directions. Use of optical tweezers with two-photon polymerization not only allowed in-situ corrective positioning of the polymerized structures, but also the integration of fluorescent microspheres (resonator/detector) with polymerized waveguide.

The total internal reflection of an optical beam with a phase singularity can generate evanescent light that displays a rotational character. At a metalized surface, in particular, field components extending into the vacuum region possess vortex properties in addition to surface plasmon features. These surface plasmonic vortices retain the phase singularity of the input light, also mapping its associated orbital angular momentum. In addition to a two-dimensional patterning on the surface, the strongly localized intensity distribution decays with distance perpendicular to the film surface. The detailed characteristics of these surface optical vortex structures depend on the incident beam parameters and the dielectric mismatch of the media. The static interference of the resulting surface vortices, achieved by using beams suitably configured to restrict lateral in-plane motion, can be shown to give rise to optical forces that produce interesting dynamical effects on atoms or small molecules trapped in the vicinity of the surface. As well as trapping within the surface plasmonic fields, model calculations reveal that the corresponding atomic trajectories will typically exhibit a variety of rotational and vibrational effects, significantly depending on the extent and sign of detuning from resonance.

High throughput analysis of trapped samples requires effective loading and unloading into the trap in a microfluidic environment. We demonstrate development of a hybrid optical transport trap (HOTT) which combines a tapered fiberoptic 2D trap for transport of microscopic objects into and out of the optical tweezers trap in an orthogonal geometry. For small cone angle of the tip, the microscopic objects (polystyrene and red blood cells) were found to be trapped in two-dimensions and pushed along the axial direction by domination of scattering force. This was found to be in consistence with the estimated axial forces caused by the beam profiles emerging from the small-cone tapered fiber tip. While for loading of the microscopic objects into the optical tweezers trap, the fiber tip was placed ~ 30μm away from the tweezers trap, unloading was carried out in presence of the tip close (<15 μm) to the tweezers trap. Further, for a fixed fiber trap and tweezers separation (~ 30 μm), both loading and unloading could be achieved by reducing the tweezers trap power so that the scattering force exerted by the fiber trap exceeded the transverse gradient force of tweezers trap. Since the tapered tip can be easily integrated onto a microfluidic channel, the proposed configuration can find potential applications in lab-on-a-chip devices. We demonstrate analysis of transported microscopic objects using digital holographic microscopy integrated with the HOTT.

For an extended wavefront analysis, structured materials processing, optical information technologies, or superresolving microscopy with ultrashort pulses, more flexible and robust techniques of beam shaping are required. Non-Gaussian fringe-free Bessel beams ("needle beams") can be generated with programmable phase maps of phase-only displays. Such beams behave propagation invariant over relatively extended regions with respect to their characteristic spatio-temporal signatures. Here, we extend the concept of needle pulses towards other types of nondiffracting fields including significantly more complex ones. It is shown that also nondiffracting light slices, tubular beams or pixellated images can be composed from simple nondiffracting constituents of higher degree of symmetry. With arrangements of multiple small phase axicons programmed into liquid-crystal-on-silicon spatial light modulators, a large variety of non-conventional nondiffracting beams of even highly asymmetrically partitions can be achieved with widely propagation invariant spectral and temporal properties. Modified Shack-Hartmann sensors with integrated temporal sensitivity, advanced types of multichannel autocorrelators and adaptive materials processing with variable focal spots are proposed.

The nanocomposites on the base of long (5-10μm, o-MWCNTs) and short (~ 2μm, m-MWCNTs) multi-walled carbon nanotubes (MWCNTs) hosted by nematic 5CB were investigated in details by means of polarizing microscopy, studies of electrical conductivity and electro-optical behaviour. The spontaneous self-organization of MWCNTs was observed and investigated both theoretically and experimentally. The efficiency of MWCNT aggregation in these composites is controlled by strong, long ranged and highly anisotropic van der Waals interactions and Brownian motion of individual nanotubes and their aggregates. The simple Smoluchowski approach was used for estimation of the half-time of aggregation. It was shown that aggregation process includes two different stages: fast, resulting in formation of loose aggregates (L-aggregates) and slow, resulting in formation of compacted aggregates (C-aggregates). Both L- and C- aggregates possess extremely ramified fractal borders. Formation of the percolation structures was observed for o-MWCNTs at C=C_p≈0.025-0.05 % wt and for m-MWCNTs at C=C_p≈0.1- 0.25 % wt. A physical model describing formation of C-aggregates with captured 5CB molecules inside was proposed. It shows good agreement with experimentally measured characteristics. It was shown that MWCNTs strongly affect the structural organization of LC molecules captured inside the MWCNT skeleton and of interfacial LC layers in the vicinity of aggregate borders. Moreover, the structure of the interfacial layer, as well as its birefringence, drastically changed when the applied electric voltage exceeded the Freedericksz threshold. Finally, formation of the inversion walls between branches of the neighbouring MWCNT aggregates was observed and discussed for the first time.

We measure the complete electric field of extremely complex ultrafast waveforms using the simple linear-optical, interferometric pulse-measurement technique, MUD TADPOLE. In its scanning variation, we measured waveforms with time-bandwidth products exceeding 65,000 with ~40 fs temporal resolution over a temporal range of ~3.5ns. In the single-shot variation we measured complex waveforms time-bandwidth products exceeding 65,000. The approach is general and could allow the measurement of arbitrary optical waveforms.

In conical refraction, when a collimated light beam passes along the optic axis of a biaxial crystal it refracts conically giving rise to a characteristic conical refraction (CR) ring. At each point of the CR ring the light electric field is linearly polarized with the polarization plane rotating along the ring such that every two opposite points of the ring present orthogonal linear polarizations. With a pinhole we have spatially filtered a small part of the CR ring and experimentally reported that this filtered light does not yield a ring pattern when it refracts along the optic axis of a second biaxial crystal, called the CR-analyzer in what follows. Instead, after crossing the CR-analyzer the filtered beam splits into two beams with orthogonal linear polarizations that correspond to two opposite points of the otherwise expected CR ring. We have experimentally derived the transformation rules of the filtered beam. For a CR-analyzer rotated by an angle ω around the optic axis, the filtered beam splits in two beams with intensities following the fermionic transformation rule cos² (ω / 2) , in contrast to the Malus law of cos ²ω followed by double refraction.

We report a new simple optical system for the highly efficient measurement of the Orbital Angular Momentum States of Light. It uses an image reformatter to map each input state onto a different lateral position in the output aperture. This, near perfect, separation of states potentially makes available the high information capacity of OAM in both classical and quantum applications.

We present experiments on Orbital Angular Momentum (OAM) induced beam shifts in optical reflection. Specifically, we observe the spatial Goos-Hänchen shift in which the beam is displaced parallel to the plane of incidence and the angular Imbert-Fedorov shift which is a transverse angular deviation from the geometric optics prediction. Experimental results agree well with our theoretical predictions. Both beam shifts increase with the OAM of the beam; we have measured these for OAM indices up to 3. Moreover, the OAM couples these two shifts. Our results are significant for optical metrology since optical beams with OAM have been extensively used in both fundamental and applied research.

We experimentally investigate Raman optical activity in the scattering of light with spin and orbital angular momentum. Varying combinations of spin and orbital angular momentum of light, associated with circular polarization and the helical phase structure of Laguerre-Gaussian modes, respectively, are generated by transforming a cylindrical vector beam into a circular polarized Laguerre-Gaussian mode. Raman back scattered light of a circular polarized Laguerre-Gaussian beam propagating along the optic axis of a c-cut uniaxial birefringent quartz sample is collected with a spectrometer. The resulting Stokes shifted spectra is analyzed and discussed in relation to traditional Raman optical activity.

It is well established that a light beam can carry angular momentum and therefore when using optical tweezers it is possible to exert torques to twist or rotate microscopic objects. Both spin and orbital angular momentum can be transferred. This transfer can be achieved using birefringent particles exposed to a Gaussian circularly polarized beam. In this case, a transfer of spin angular momentum will occur. The change in spin, and hence the torque, can be readily measured optically. On the other hand, it is much more challenging to measure orbital angular momentum and torque. Laguerre-Gauss mode decomposition, as used for orbital angular momentum encoding for quantum communication, and rotational frequency shift can be used, and are effective methods in a macro-environment. However, the situation becomes more complicated when a measurement is done on microscale, especially with highly focused laser beams. We review the methods for the measurement of the angular momentum of light in optical tweezers, and the challenges faced when measuring orbital angular momentum. We also demonstrate one possible simple method for a quantitative measurement of the orbital angular momentum in optical tweezers.

In optics, the Goos-Hänchen shift is a transverse displacement of a reflected light beam along a material interface. It is usually associated with the presence of evanescent waves beyond the interface. We describe an analogous displacement effect for scalar waves at a boundary satisfying Robin, or mixed, boundary conditions, although the wave does not penetrate the boundary. We briefly discuss how the reflection of electromagnetic plane waves differs from reflection due to Robin boundary conditions.

A method for the generation of cylindrical vector beams based on the design of a multicore optical fiber is presented. This design consists of N elliptical cores symmetrically arranged in a circular array about the fiber axis, where the orientation of each core's major axes has an azimuthally varying distribution. A cylindrically symmetric amplitude and polarization state is produced in the far field of the fiber output by the coherent superposition of the individual core outputs. Such a fiber with N=6 cores is fabricated and experimentally investigated. Numerical simulations show the dependence of the far field intensity of an array of Gaussian beamlets on the number of beamlets and their spacing in the array.

Numerous theoretical and experimental studies have established the principle that beams conveying orbital angular momentum offer a rich scope for information transfer. However, it is not clear how far it is practicable to operate such a concept at the single-photon level - especially when such a beam propagates through a system in which scattering can occur. In cases where scattering leads to photon deflection, it produces losses; however in terms of the retention of information content, there should be more concern over forward scattering. Based on a quantum electrodynamical formulation of theory, this paper aims to frame and resolve the key issues. A quantum amplitude is constructed for the representation of single and multiple scattering events in the propagation an individual photon, from a suitably structured beam. The analysis identifies potential limitations of principle, undermining complete fidelity of quantum information transmission.

We study laser induced spin-orbit (SO) coupling in cold atom systems where lasers couple three internal states to a pair of excited states, in a double tripod topology. Proper choice of laser amplitudes and phases produces a Hamiltonian with a doubly degenerate ground state separated from the remaining "excited" eigenstates by gaps determined by the Rabi frequencies of the atom-light coupling. After eliminating the excited states with a Born- Oppenheimer approximation, the Hamiltonian of the remaining two states includes Dresselhaus (or equivalently Rashba) SO coupling. Unlike earlier proposals, here the SO coupled states are the two lowest energy "dressed" spin states and are thus immune to collisional relaxation. Finally, we discuss a specific implementation of our system using Raman transitions between different hyperfine states within the electronic ground state manifold of nuclear spin I = 3/2 alkali atoms.

Optical trapping and manipulation have established a track record for cell handling in small volumes. However, this cell handling capability is often not simultaneously utilized in experiments using other methods for measuring single cell properties such as fluorescent labeling. Such methods often limit the trapping range because of high numerical aperture and imaging requirements. To circumvent these issues, we are developing a BioPhotonics Workstation platform that supports extension modules through a long working distance geometry. Furthermore, a long range axial manipulation range is achieved by the use of counter-propagating beam traps coupled with the long working distance. This geometry provides three dimensional and real time manipulation of a plurality of traps - currently 100 independently reconfigurable - facilitating precise control and a rapid response in all sorts of optical manipulation undertakings. We present ongoing research activities for constructing a compact next generation BioPhotonics Workstation.

Three dimensional finite element method is employed to determine optical trapping forces on hollow glass spheres on an optical waveguide. The evanescent field from the waveguide interacts mostly with the shell of the hollow glass sphere. We describe how the optical forces vary with shell thickness and particle size, and find the minimum shell thickness allowing trapping and propulsion of hollow glass spheres. Hollow glass spheres with shell thickness less than the minimum are repelled away from the optical waveguide. The simulation results are compared with analytical Mie calculations and experimental data.

In its standard version, our BioPhotonics Workstation (BWS) can generate multiple controllable counter-propagating beams to create real-time user-programmable optical traps for stable three-dimensional control and manipulation of a plurality of particles. The combination of the platform with microstructures fabricated by two-photon polymerization (2PP) can lead to completely new methods to communicate with micro- and nano-sized objects in 3D and potentially open enormous possibilities in nano-biophotonics applications. In this work, we demonstrate that the structures can be used as microsensors on the BWS platform by functionalizing them with silica-based sol-gel materials inside which dyes can be entrapped.

In this paper, we explore the propagation of light through disordered material and ask whether we can create an optimal focus in such a scenario. We use the complex modulation of the input light (i.e. modulation in both phase and amplitude) for these studies, implemented by use a spatial light modulator (SLM) and show trapping and manipulation through a static turbid medium. We then extend the system to create a tandem SLM system with an acousto-optic deflector. This has further advantages as we can now not only project light fields into turbid media but can also create interference-free mode superpositions of light fields such as Laguerre-Gaussian (LG) and Bessel modes. This is illustrated by controlled rotation of trapped particles in weighted, interference-free superpositions of LG beams of opposite order but equal magnitude.

We present a geometric phase arising from transformations along the surface of a Poincare sphere representation for cylindrical vector beams. Cylindrical vector beams are expressed as the superposition of orthogonal circular polarized Laguerre-Gaussian modes of opposite topological charge. Two spheres are described where the poles of each sphere are circular polarized Laguerre-Gaussian modes, and points along the equator are cylindrical vector beams. A closed loop transformation on the sphere's surface is carried out using combinations of wave plates and cylindrical lens mode converters, and an acquired geometric phase is experimentally measured interferometrically.

Stochastic vortex fields are found in laser speckle, in scintillated beams propagating through a turbulent atmosphere, in images of holograms produced by Iterative Fourier Transform methods and in the beams produced by certain diffractive optical elements, to name but a few. Apart from the vortex fields found in laser speckle, the properties and dynamics of stochastic vortex fields are largely unexplored. Stochastic vortex fields with non-equilibrium initial conditions exhibit a surprisingly rich phenomenology in their subsequent evolution during free-space propagation. Currently there does not exist a general theory that can predict this behavior and only limited progress has thus far been made in its understanding. Curves of the evolution of optical vortex distributions during free-space propagation that are obtained from numerical simulations, will be presented. A variety of different stochastic vortex fields are used as input to these simulations, including vortex fields that are homogeneous in their vortex distributions, as well as inhomogeneous vortex fields where, for example, the topological charge densities vary sinusoidally along one or two dimensions. Some aspects of the dynamics of stochastic vortex fields have been uncovered with the aid of these numerical simulations. For example, the numerical results demonstrate that stochastic vortex fields contain both diffusion and drift motions that are driven by local and global variations in amplitude and phase. The mechanisms for these will be explained. The results also provide evidence that global variations in amplitude and phase are caused by variations in the vortex distributions, giving rise to feedback mechanisms and nonlinear behavior.

Optical vortices are points of zero intensity in a two dimensional, classical optical field. As first discussed by Berry and Dennis [Berry, M. V. and Dennis, M. R., "Quantum cores of optical phase singularities" Journal of Optics A 6, S178-S180 (2004)] these singularities are replaced by 'quantum cores' in a deeper level of description. In a fully quantized theory of optical fields an excited atom trapped at the singularity can emit light spontaneously and hence soften the perfect zero of an optical vortex. More recently Barnett [Barnett, S. M., "On the quantum cores of a optical vortex," Journal of Modern Optics 55, 2279-2292 (2008)] presented a more realistic analysis of quantum cores which accounts for the effect of the trapping potential on the transition dynamics inside a vortex core. Here, we revisit the scenario of emission near an optical vortex in the realistic setting of Barnett.

We demonstrate an on-chip microparticle passive sorting device employing a 3-dB optical splitter that consists of a slot waveguide and a conventional channel waveguide. Simulations indicate that the optical force in the vertical direction exerted on small particles (d < 1 μm) by the slot waveguide is larger than that by the channel waveguide. On the other hand, the channel waveguide provides a stronger vertical force on large particles (d > 1 μm) than the slot waveguide. The in-plane optical force provides a double-well trapping potential for small particles only. We perform experiments in which small (320 nm diameter) and large (2 μm diameter) particles are brought to the splitter by the channel waveguide. Due to a structural perturbation provided by a stuck bead, the small particles are transferred to the slot waveguide. The large particles remain on the channel waveguide. The automated nature of this method, along with the low guided power employed (20 mW in these experiments), makes this a promising approach for sorting sub-micron particles.

We present the use of n - phase cylindrical vector beams in optical trapping. The vector beams are created via a Mach- Zehnder interferometer equipped with tunable phase plates, and the "n" prefix indicates the relative phase between the Hermite-Gaussian modes comprising the output beam. The optical trapping efficiency is measured via the Stokes drag force method for radial and azimuthal vector beams with n = 0 and π, giving a total of 4 unique input beams. Additionally, their trapping efficiencies are compared with that of a standard Gaussian input beam of equal input power. We find that the axial trapping efficiency can be optimized by increasing the amount of longitudinal (z) polarization at the focal plane of the trapping objective. Further, the lateral trapping efficiency is determined by the focal spot diameter, as expected, and can be similarly tuned by varying the relative phase between the vector beams' eigenmodes. The results suggest that cylindrical vector beams may be tuned such that both axial and lateral trapping efficiencies can be maximized.

We report a method to optically trap and micromanipulate metallic particles using IR laser. The experiment demonstrates the trapping of metallic particle using low NA objective lens (0.6 N.A). Unlike single beam gradient trapping of dielectric objects, the optical trapping of metallic particles occurs due to diffraction effect. We thus provide evidence for non-gradient forces playing a dominant role in the trapping of metallic particles, in here for the case of 3μm Fe particles, efficient trapping occurs at off-axis position (in the side lobes) of a focused laser beam. The optical trap is characterized by measuring the external magnetic field required to dislodge the Fe particle, and was found to be 0.03T to 0.11T for laser power 5 to 55mW at the sample.

We experimentally demonstrate the generation of a class of spatially variant polarization beams called hybrid vector beams. Hybrid vector beams have cylindrically symmetric amplitude and a spatially varying degree of polarization ellipticity in their transverse profile about the beam axes, varying from linear to elliptical to circular every 45 degrees. We describe a method for the generation of various hybrid vector beam polarizations based on the transformation of various cylindrical vector beams using conventional wave plates. The Stokes parameters for the overall polarization of each hybrid vector beam generated are experimentally measured and mapped numerically.