This PDF file contains the front matter associated with SPIE Proceedings Volume 8637, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

In 1992 Allen et al. recognized that light beams could carry an angular momentum in addition to that arising from the photon spin. This orbital angular momentum can be created using lenses or diffractive optics, the later often formed using liquid crystal displays. Both whole beams and single photons can carry this twist, and transfer it to particles causing them to spin. This paper introduces the underlying principles of orbital angular momentum and reviews a number of its manifestations and applications. These effects highlight how optics still contains surprises and opportunities for manipulation, imaging and communication in both the classical and quantum worlds.

We obtain a well-defined topological charge signature from the intensity correlation of two spatially incoherent Laguerre-Gauss beams of differing orders when each beam is diffracted by a triangle. We show that the value of the obtained topological charge follows a correlation rule such that its value is related to the topological charges associated to both incoherent beams. This paper suggests a way to measure an effective topological charge of the coherence function, and opens a new window for studies of correlation between different orders of optical vortex beams.

We image optical singularities by exploiting the connection between scalar and vector fields. We examine the sensitivity of optical vortices to perturbations and suggest a method of study via imaging polarimetry of the optical field. This is possible by converting optical vortices to polarization-singularity C-points. We present the deliberate creation of C-points using a superposition of two circularly polarized beams of opposite helicity, with a phase vortex in one and a planar wavefront in the other. We present a theoretical analysis and measurements of the transformation of C-points from lemon to star, going through the monstar stage. We do this by varying the phase gradient of the optical vortex.

For a plane electromagnetic wave, where the electric and magnetic fields are precisely disposed in the transverse plane and the Poynting vector is parallel to the propagation vector, it is well known that the classical text-book analysis of angular momentum density gives a vanishing result for any longitudinal component. In particular, under these assumptions, a circularly-polarized wave (or photon) might be construed to have no angular momentum in the propagation direction. Of course this is untrue; indeed it is the basis of Beth’s famous measurement of spin angular momentum for circularly polarized light that a torque is exerted about the beam axis. This presentation reviews some of the calculational aspects, and the associated physics, involved in a resolution of the issue. In particular it is shown unnecessary to artificially impose on the beam a transverse intensity profile, vanishing at infinity, to resolve the matter. For optical beams of arbitrary structure, promotion of the electromagnetic fields, and associated potentials, to operator form gives non-zero values to each of the commonly deployed electromagnetic measures of physical significance; with a quantum optical formulation, results are cast in terms of Hermitian operators and duly relate to physical observables. Thus, not only energy and angular momentum, but also measures of chirality such as the ‘Lipkin zilch’, acquire a consistent physical interpretation

We report on the first experimental demonstration of resonant optical trapping of dielectric particles in a two-dimensional hollow photonic crystal cavity. The cavities are implemented in an optofluidic chip consisting of a silicon-on-insulator substrate and an ultrathin microfluidic membrane, Resonant optical trapping of 500 nm polystyrene beads is achieved using less than 120 μW optical power in the cavity for trapping times reaching over ten minutes.

Optical vortices possess several special properties, including carrying optical angular momentum (OAM) and exhibiting zero intensity. Vortex array laser beams have attracts many interests due to its special mesh field distributions, which show great potential in the application of multiple optical traps and dark optical traps. Previously study developed an Ince-Gaussian Mode (IGM)-based vortex array laser beam¹. This study develops a simulation model based on the discrete dipole approximation (DDA) method for calculating the resultant force acting on a micro-sized spherical dielectric particle that situated at the beam waist of the IGM-based vortex array laser beams¹.

By using digital holograms, we present a simple technique for performing a complete azimuthal decomposition of an arbitrary laser mode. The match-filter, used to perform the azimuthal decomposition, is bounded by an annular ring, allowing us to conduct a scale-independent decomposition on our selected mode. This technique therefore requires no prior knowledge of the mode structure, the mode phases, or the amplitude distribution. A basis comprising of the angular harmonics is used to express the spatial distribution of the selected mode in terms of spatially dependant coefficients. We use this to infer directly from the measured weightings of the azimuthally decomposed modes and their phase-delay measurements, the intensity of the selected field, its phase, and its orbital angular momentum (OAM) density. We illustrate the concept by executing a full decomposition of two examples: a superposition of two Bessel beams, with relative phase differences, and an off-axis vortex mode. We show a reconstruction of the amplitude, phase and OAM density of these fields with a high degree of accuracy.

Using SU(N) group theory, we develop a formalism to superimpose N vortex modes and form N orthogonal principal states in fiber. These principal states provide a means to overcome the detrimental effects of mode coupling that occur in optical communications links. This formalism reduces to the Jones matrix eigenanalysis when N equals 2, which has been studied extensively to characterize polarization mode dispersion. Specifically we use the 4 vortex modes of the LP11 modal group to establish the principal states and we graphically display them using the higher order Poincare sphere, HOPS.

For polarization mode dispersion and N = 2, we require 3 Pauli spin matrices and consequently 3 mux demux components to generate the Principal states. For N = 3, we use the 8 Gell Mann matrices and 8 components. For N = 4 as is the case for 4 the vortex modes of the LP11 modal group, we require 15 generators and 15 physical components, since these systems scale as N^2-1. The LP11 modal group includes the HE21 horizontal and vertical vortex modes as well as the transvers electric and transverse magnetic vortex modes.

As an example, we describe in some detail a link with 3 and separately one with 4 principal states, which are superimposed from the vortex modes. We also show schematically the active and passive components required to multiplex and demultiplex the principal states.

We present a powerful approach towards full understanding of laser light propagation through multimode optical fibres and control of the light at the fibre output. Transmission of light within a multimode fibre introduces randomization of laser beam amplitude, phase and polarization. We discuss the importance of each of these factors and introduce an experimental geometry allowing full analysis of the light transmission through the multimode fibre and subsequent beam-shaping using a single spatial light modulator. We show that using this approach one can generate an arbitrary output optical field within the accessible field of view and range of spatial frequencies given by fibre core diameter and numerical aperture, respectively, that contains over 80% of the total available power. We present applications of these approaches in biophotonics and imaging. We show the confinement and manipulation of a number of microparticles using the output field of the multimode fibre. We demonstrate the modalities of bright-field and dark-field imaging and scanning fluorescence microscopy at acquisition rates allowing observation of dynamic processes such as Brownian motion of mesoscopic particles. Furthermore, we show how such control can realise a new form of mode converter and generate various types of advanced light fields such as propagation-invariant beams and optical vortices. These may be useful for future fibre based implementations of super-resolution or light sheet microscopy.

Propagation invariant, ‘non-diffracting’ beams have found numerous applications in areas as diverse as filamentation, trapping, and photoporation. However, the prominent transverse structure of Bessel beams prevents localized illumination, thus hampering its use for high resolution imaging with an extended focus. We investigate the relationship between axial resolution, contrast, and propagation invariance for single and two-photon fluorescence light sheet microscopy.

We demonstrate the efficient generation of line patterns using matched-filtering Generalized Phase Contrast (mGPC). So far, the main emphasis of mGPC light addressing has been on the creation of rapidly reconfigurable focused spots. This has recently been extended to encoding extended line patterns for structured light applications and advanced microscopy.

For a growing number of applications in nonlinear spectroscopy, micro- and nano-machining, optical data processing, metrology or medicine, an adaptive shaping of ultrashort pulsed, ultrabroadband laser beams into propagation-invariant linear focal zones (light blades) is required. One example is the femtosecond laser high-speed large area nanostructuring with moving substrates and cylindrical optics we reported about recently. Classical microoptical systems, however, distort the temporal pulse structure of few cycle pulses by diffraction and dispersion. The temporal pulse transfer can be improved with innovative types of reflective MEMS axicons based on two integrated rectangular mirrors, tilted by a piezoelectric bending actuator. In contrast to pixelated liquid-crystal-on-silicon (LCoS) based devices, cutoff frequencies in multi-kilohertz range, a purely reflective setup and continuous profiles with larger phase shift are realized which enable for shaping extended propagation-invariant zones at a faster and more robust operation. Additionally, a fixed phase offset can be part of the structure. Here, the performance of a prototype of linear mechanically tunable MEMS axicon is demonstrated by generating a pseudo-nondiffracting line focus of variable diameter and depth extension from a femtosecond laser pulse. The temporal transfer of 6-fs pulses of a Ti:sapphire laser oscillator is characterized with spectral phase interferometry for direct electric-field reconstruction (SPIDER) and spatially resolved nonlinear autocorrelation. Spatial and temporal self-reconstruction properties were studied. The application of the flexible focus to the excitation of plasmon-polaritons and the self-organized formation of coherently linked deep sub-wavelength laser-induced periodic surface structures (LIPSS) in semiconductors and dielectrics is reported.

This study proposed a method for calculating any arbitrarily linear polarization paraxial optical field propagation in Gradient-index (GRIN) lens. The proposed method uses multiple thin-phase sheets to approximate a GRIN lens. This study also compares the proposed method with the other well-known method. That is, using a single lens equivalent optical system of Fractional Fourier transform (FrFT) to simulate a GRIN lens. The evolution in GRIN lenses of many special beams have been calculated by the FRFT-method. This study use both methods to calculate the Helmholtz-Gauss beam evolution in GRIN lenses of a small and a high gradient constant, respectively. Numerical results shows that the differences between two calculation methods appeared while the GRIN lens of a high gradient constant. This study provides an alternative approach could calculate the linearly polarized field evolution in GRIN lenses with higher precision, which will be useful to the optical design of GRIN lens systems.

The orbital angular momentum of light, and also of waves beyond the electromagnetic spectrum, is a powerful concept in all systems with cylindrical or rotational symmetry. Expressing quantum images in terms of orbital angular momentum modes allows one to describe image rotations in terms of OAM dependent phase shifts. We discuss image rotations, and in particular Faraday rotations in optical systems, and predict a Faraday rotation for electron vortices. Our considerations highlight connections between orbital angular momentum features in different systems, in particular between image rotations in optical and electron systems, and also between parametric processes in parametric down-conversion and atomic cascades. We compare the phasematching conditions of the two latter systems and demonstrate the efficient transfer of OAM modes and their superpositions from near-infrared pump light to blue light in a four-wave mixing process in rubidium vapour.

The OAM or spiral bandwidth indicates the dimensionality of an entangled state that is produced by the spontaneous parametric down-conversion process. Normally this bandwidth is determined by modulating the signal and idler beams with helical phase functions with opposite azimuthal indices on the spatial light modulators in the signal and idler beams, respectively. We added an additional binary Bessel function to the helical phase, thereby specifying the radial dependence of the mode to be Bessel-Gaussian (BG) modes. This comes down to a post selection process, which is known to have the ability to increase entanglement. The result is a modification to the shape of the OAM spectrum, which leads to a higher dimensionality for the quantum states. We perform analytical calculations to show that the bandwidths obtained by measuring in the BG modal basis are larger than those for the LG modes. These theoretical predictions are confirmed by experimental measurements of the bandwidths for LG modes and for BG modes with different transverse scales.

Commercially available supercontinuum sources continue to experience a strong growth in a wide range of industrial and scientific applications. In addition, there is a significant research effort focused on extending the wavelength coverage both towards UV and Mid-IR. Broadband sources covering these wavelength regions have received significant attention from potential users, as there is a wide array of applications for which there are few suitable alternative light sources – if any. Our developments in the field of Mid-IR supercontinuum sources have been based on radical approaches; such as soft glasses and novel pumping schemes, whereas shifting the spectrum further towards the UV has been based on sophisticated microstructure fiber designs. Here we present our latest developments in tailoring the power and spectral coverage of spatially coherent broadband supercontinuum sources.

He-Ne laser (0.63 mkm) initiates developing singular speckle-fields due to «optical damage» in photorefractive LiNbO₃: Fe crystal. They were investigated by techniques of dynamic stocks-polarimetry, monstardom and polarization characteristics of optical vortices combined with morphology of polarization singularities. Ergodicity of dynamic speckle-fields was found. It was shown that sign of C points coincides with speckle handedness they are nested; stars/monstar, lemon are underlined by negative/positive OVs. General regularities of dynamic elliptic speckle-fields development were established.

Microstructure, phase transitions, electrical conductivity, and optical and electrooptical properties of multiwalled carbon nanotubes (NTs), dispersed in the cholesteric liquid crystal (cholesteryl oleyl carbonate, COC), nematic 5CB and their mixtures, were studied in the temperature range between 255 K and 363 K. The relative concentration X=СОС/(СОС+5CB) was varied within 0.0-1.0. The concentration C of NTs was varied within 0.01-5% wt. The value of X affected agglomeration and stability of NTs inside СОС+5CB. High-quality dispersion, exfoliation, and stabilization of the NTs were observed in COC solvent (“good” solvent). From the other side, the aggregation of NTs was very pronounced in nematic 5CB solvent (“bad” solvent). The dispersing quality of solvent influenced the percolation concentration C_p, corresponding to transition between the low conductive and high conductive states: e.g., percolation was observed at C_p≈1% and C_p≈0.1% for pure COC and 5CB, respectively. The effects of thermal pre-history on the heating-cooling hysteretic behavior of electrical conductivity were studied. The mechanism of dispersion of NTs in COC+5CB mixtures is discussed. Utilization of the mixtures of “good” and “bad” solvents allowed fine regulation of the dispersion, stability and electrical conductivity of LC+NTs composites. The mixtures of COC and 5CB were found to be promising for application as functional media with controllable useful chiral and electrophysical properties.

We have demonstrated efficient propagation of the first excited TE01, TM01, and HE21 modes in a nanofiber with a radius of 400 nm. As we decrease the taper angle from 4 mrad to 1 mrad, the propagation becomes more adiabatic and the transmission improves from 20% to 85%. We have also demonstrated that the choice of drawn fiber can have a significant impact on the propagation characteristics.

We demonstrate the use of microfabricated supporting structures for maneuvering and supporting polystyrene microspheres for use as magnifying lenses in imaging applications. The supporting structure isolates the trapping light from the magnifier, hence avoiding direct radiation to the sample being observed which could be damaging, especially for biological specimens. Using an optical trapping setup, we demonstrate the actuation of a microsphere not held by optical traps, and show the possibility of imaging through such microspheres.

Holographic optical tweezers have been developed for the manipulation of polymeric microparticles or biological cells with almost circular shape. As is well known, spherical particles can be trapped and controlled by optical tweezers and assembled with an additional light modulator application. Complementary building blocks, which are used in the following experiments, are generated by a two-photon-polymerization process in micrometer range and are not equipped with spherical trapping points. The possibilities of manufacturing arbitrary building blocks within the 2PP process and the potential of HOTs lead to the idea of combining manufacturing techniques with manipulation processes in a bottomup operation. In this work we present an experimental setup with an integrated fiber laser for holographic optical trapping of non-spherical building blocks. Furthermore experimental requirements which permit trapping will be illustrated.

The motion of a colloidal particle in an optical field depends on a complex interplay between the structure of the field, and the geometry and composition of the particle. There are two complementary approaches to generating a particular force field. The first, involving shaping the optical field with e.g. a spatial light modulator, has been extensively developed. A second method, highlighted recently [J. Gluckstad, Nature Photonics, 5, 7–8 (2011)] involves sculpting of the particles themselves, and has received less attention. However, as modern two-photon polymerisation methods advance, this avenue becomes increasingly attractive for micromanipulation. In this paper we will show how computational methods may be used to optimise particle geometries to produce desirable patterns of forces and torques. In particular, we will examine the design of a constant force optical spring for use as a passive force clamp, and the effect of particle size on the trapping of prolate spheroids.

In the current work we intend to use the optical nano-antenna to include various functionalities for the recently demonstrated waveguided optical waveguide (WOW) by Palima et al. (Optics Express 2012). Specifically, we intend to study a WOW with an optical nano-antenna which can block the guiding light wavelength while admitting other wavelengths of light which address certain functionalities, e.g. drug release, in the WOW. In particular, we study a bow-tie optical nano-antenna to circular dielectric waveguides in aqueous environments. It is shown with finite element computer simulations that the nanoantenna can be made to operate in a bandstop mode around its resonant wavelength where there is a very high evanescent strong electrical probing field close to the antennas, and additionally the fluorescence or Raman excitations will be be unpolluted by stray light from the WOW due to the band-stop characteristic. We give geometrical parameters necessary for realizing functioning nanoantennas.

Hollow, metal-lined capillary waveguides have recently been utilized in spontaneous gas-Raman spectroscopy to improve signal strength and response time. The hollow waveguide is used to contain the sample gases, efficiently propagate a pump beam, and efficiently collect Raman scattering from those gases. Transmission losses in the waveguide may be reduced by using an azimuthally polarized pump beam instead of a linearly or radially polarized pump. This will lead to improved Raman signal strength, accuracy, and response time in waveguide-based Raman gas-composition sensors. A linearly polarized laser beam is azimuthally polarized using passive components including a spiral phase plate and an azimuthal-type linear analyzer element. Half-wave plates are then used to switch between the azimuthally polarized beam and the radially polarized beam with no change in input pump power. The collected Raman signal strength and laser-throughput are improved when the azimuthally polarized pump is used. Optimization of the hollow waveguide Raman gas sensor is discussed with respect to incident pump polarization.

Compared to conventional optics like singlet lenses or even microscope objectives advanced optical designs help to develop properties specifically useful for efficient optical tweezers. We present an optical setup providing a customized intensity distribution optimized with respect to large trapping forces. The optical design concept combines a refractive double axicon with a reflective parabolic focusing mirror. The axicon arrangement creates an annular field distribution and thus clears space for additional integrated observation optics in the center of the system. Finally the beam is focused to the desired intensity distribution by a parabolic ring mirror. The compact realization of the system potentially opens new fields of applications for optical tweezers such as in production industries and micro-nano assembly.

We demonstrate experimentally a new method of sorting of colloidal particle suspension in wide single laser beam. The sorting is performed in a realization of a “tractor” beam a weakly focused laser beam that is retro-reflected under an oblique angle. In this configuration the lateral positions of particles dependent on the direction of linear polarization of the beam. Polarization rotation by 90 degrees changes the sign of the lateral optical force acting upon particles of certain properties and such particles are propelled in the opposite direction. This approach provides surprisingly efficient way of passive sorting of tens of particles by pure switching the beam polarization.

The study of nonparaxial fields through the complex focus model is discussed. This model can be used to rep- resent fields with linear, circular, elliptical, radial, azimuthal, and full Poincar´e polarizations. Other interesting beam distributions include nonparaxial Airy-Gauss beams. Further, complete bases are proposed that allow the expansion of arbitrary focused fields. The Mie scattering for any of these fields is given in closed form, for any position of the particle, allowing analytic calculations of the forces and torques. Finally, these analytic expressions lend themselves to the study of the interaction between orbital and spin angular momenta in the nonparaxial regime.

We introduce the correlation filter method for measuring the modal power spectrum of multi-mode beams. The method is based on an optical filter performing the integral relation of correlation. This filter is realized as a computer-generated hologram with a specifically designed transmission function based on the spatial distribution of the set of modes under test. The beam that is illuminating the hologram is generating a diffraction pattern containing information about modal amplitudes and intermodal phase differences. We will show that a simple single-shot intensity measurement is sufficient to gain the information about modal amplitudes and phases from the diffraction pattern which result in the ability to reconstruct the optical field under test. Beside a detailed presentation of the measurement process, the setup and the design of the correlation filters, the major advantage of the method, the ability to perform real-time measurements is introduced. As a test system, we investigate the guided modes of a few mode multi-mode fiber and show fast changing modal coupling processes. Thereby, we show measurement results of online-monitoring the reconstructed optical field of the beam under test.

Diamond anvil cells allow us to study the behaviour of materials at pressures up to hundreds of gigaPascals in a small and convenient instrument, however physical access to the sample is impossible once it is pressurised. Optical tweezers use tightly focussed lasers to trap and hold microscopic objects, and their ability to measure nanometric displacements and femtonewton forces makes them ubiquitous across the nano and bio sciences. We show that optical tweezers can be used to hold and manipulate particles in such a cell, in the ``macro tweezers'' geometry allowing us to use objective lenses with a higher working distance. Traps are structured to overcome the limitations imposed by the sample cell. Wedemonstrate the effectiveness of the technique by measuring water's viscosity up to 1.2 GPa. The maximum pressure reached was limited by the water crystallising under pressure.

We present a novel technique to measure the orbital angular momentum (OAM) density of light. The technique is based on modal decomposition, enabling the complete reconstruction of optical fields, including the reconstruction of the beams Poynting vector and the OAM density distribution. The modal decomposition is performed using a computer-generated hologram (CGH), which allows fast and accurate measurement of the mode spectrum. The CGH encodes the modes of interest, whose powers and relative phase differences are measured from the far-field diffraction pattern of the illuminating optical field with the hologram transmission function. In combination with a classical measurement of Stokes parameters, including a polarizer and a quarter-wave plate in front of the hologram, the polarization state of each mode is measured. As a consequence, any arbitrary vector field can be reconstructed, including amplitude, phase, and polarization. Having all information on the optical field, the Poynting vector and the OAM density can be calculated directly. We applied our method to beams emerging from optical fibers, which allows us to investigate arbitrary coherent superposition of fiber modes with complexly shaped intensity and polarization distributions. The excitation of certain mode mixtures is done by appropriate input coupling and using diffractive phase masks to shape the input beam and hence enhance the excitation efficiency of distinct modes. The accuracy of the achieved results is verified by comparing the reconstructed with the directly measured beam intensity, revealing excellent agreement.

Interference of fiber eigen vector modes of different phase and spatial variation of polarization gives rise to different types of polarization singularities – isolated C-point surrounded by star / lemon type polarization morphology patterns, a dipole or two C-points of same index – in 2D polarization fields. In this context, fiber modal decomposition refers to identifying the constituent modes, their relative amplitude and the phase relationship among them in the fiber output. The size and location of the L-contour and the location of Cpoints determine the relative amplitude and the orientation of the polarization morphology pattern provides information regarding the relative phase difference between the constituent vector modes. We use these aspects of polarization singularity to demonstrate a novel fiber modal decomposition method.

A procedure to efficiently sort orbital angular momentum (OAM) states of light, by performing a Cartesian to log-polar coordinate transformation which translates helically phased beams into a transverse phase gradient, currently exists1. We implement this mode transformer, which comprises of two custom refractive optical elements2, to efficiently sort Bessel beams carrying OAM. Introducing two cylindrical lenses, allows the focusing of each of the input OAM Bessel states to a different lateral position in the Fourier plane and separates the radial wave-vectors in the image-plane. We demonstrate the concept by separating over forty OAM states and radial wave-vectors.