Generation of a Lattice of Spin-Orbit Beams via Coherent Averaging

Measuring the visual angle of polarization-related entoptic phenomena using structured light

The ability to perceive polarization-related entoptic phenomena arises from the dichroism of macular pigments held in Henle's fiber layer of the retina and can be inhibited by retinal diseases, such as age-related macular degeneration, which alters the structure of the macula. Structured light tools enable the direct probing of macular pigment density and retinal structure through the perception of polarization-dependent entoptic patterns. Here, we directly measure the visual angle of an entoptic pattern created through the illumination of the retina with a structured state of light and a perception task that is insensitive to corneal birefringence. The central region of the structured light stimuli was obstructed, with the size of the obstruction varying according to a psychophysical staircase. Two stimuli, one producing 11 azimuthal fringes and the other three azimuthal fringes, were presented to 24 healthy participants. The pattern with 11 azimuthal fringes produced an average visual angle threshold of 10° ± 1° and a 95% confidence interval (C.I.) of [6°, 14°]. For the pattern with three azimuthal fringes, a threshold extent of 3.6° ± 0.3° C.I. = [1.3°, 5.8°] was measured, a value similar to the published extent of Haidinger's brush (4°). The increase in apparent size and clarity of entoptic phenomena produced by the presented structured light stimuli offers the potential to detect the early signs of macular disease over perception tasks using uniform polarization stimuli.

Phase vortex lattices in neutron interferometry

Neutron Orbital Angular Momentum (OAM) is an additional quantum mechanical degree of freedom, useful in quantum information, and may provide more complete information on the neutron scattering amplitude of nuclei. Various methods for producing OAM in neutrons have been discussed. In this work we generalize magnetic methods which employ coherent averaging and apply this to neutron interferometry. Two aluminium prisms are inserted into a nested loop interferometer to generate a phase vortex lattice with significant extrinsic OAM, 〈Lz〉 ≈ 0.35, on a length scale of ≈ 220 μm, transverse to the propagation direction. Our generalized method exploits the strong nuclear interaction, enabling a tighter lattice. Combined with recent advances in neutron compound optics and split crystal interferometry our method may be applied to generate intrinsic neutron OAM states. Finally, we assert that, in its current state, our setup is directly applicable to anisotropic ultra small angle neutron scattering.

Structured light enhanced entoptic stimuli for vision science applications

The dichroic macular pigment in the Henle fiber layer in the fovea enables humans to perceive entoptic phenomena when viewing polarized blue light. In the standard case of linearly polarized stimuli, a faint bowtie-like pattern known as the Haidinger's brush appears in the central point of fixation. As the shape and clarity of the perceived signal is directly related to the health of the macula, Haidinger's brush has been used as a diagnostic marker in studies of early stage macular degeneration and central field visual dysfunction. However, due to the weak nature of the perceived signal the perception of the Haidinger's brush has not been integrated with modern clinical methods. Recent attempts have been made to increase the strength of the perceived signal by employing structured light with spatially varying polarization profiles. Here we review the advancements with the structured light stimuli and describe the current challenges and future prospects.

Generation of a higher-order Poincaré sphere beam array with spatial coherence engineering

We propose a protocol to synthesize a class of vector beam array in the far field with periodic higher-order Poincaré sphere (HOPS) polarization states by engineering the second-order spatial coherence structure of a partially coherent light source. We show that the polarization state of a single HOPS beam at the source plane can be mapped into a beam array in the far field when the spatial coherence of the beam source is engineered to have a lattice-like distribution. We demonstrate that the degree of polarization of the generated HOPS beam array can be conveniently controlled by modulating the transverse spatial coherence width of the source. Our method provides an additional way to construct the structured beam array and may find applications, e.g., in multiparticle manipulations.

Method for the definitive detection of orbital angular momentum states in neutrons by spin-polarized 3He

A standard method to detect thermal neutrons is the nuclear interaction 3He(n,p)3H. The spin dependence of this interaction is also the basis of a neutron spin-polarization filter using nuclear polarized 3He. We consider the corresponding interaction for neutrons placed in an intrinsic orbital angular momentum (OAM) state. We derive the relative polarization-dependent absorption cross sections for neutrons in an L = 1 OAM state. The absorption of those neutrons results in compound states J π = 0 - , 1 - , and 2 - . Varying the three available polarizations tests that an OAM neutron has been absorbed and probes which decay states are physically possible. We describe the energetically likely excited states of 4He after absorption, taking account of the odd parity of the compound state. This provides a definitive method for detecting neutron OAM states and suggests that intrinsic OAM states offer the possibility to observe new physics, including anomalous cross sections and new channels of radioactive decay.

Human psychophysical discrimination of spatially dependant Pancharatnam-Berry phases in optical spin-orbit states

We tested the ability of human observers to discriminate distinct profiles of spatially dependant geometric phases when directly viewing stationary structured light beams. Participants viewed polarization coupled orbital angular momentum (OAM) states, or "spin-orbit" states, in which the OAM was induced through Pancharatnam-Berry phases. The coupling between polarization and OAM in these beams manifests as spatially dependant polarization. Regions of uniform polarization are perceived as specifically oriented Haidinger's brushes, and study participants discriminated between two spin-orbit states based on the rotational symmetry in the spatial orientations of these brushes. Participants used self-generated eye movements to prevent adaptation to the visual stimuli. After initial training, the participants were able to correctly discriminate between two spin-orbit states, differentiated by OAM [Formula: see text], with an average success probability of [Formula: see text] ([Formula: see text], [Formula: see text]). These results support our previous observation that human observers can directly perceive spin-orbit states, and extend this finding to non-rotating beams, OAM modes induced via Pancharatnam-Berry phases, and the discrimination of states that are differentiated by OAM.

Direct discrimination of structured light by humans

Recent technological advances have enabled the creation of custom light fields with remarkable properties. Here we report an experiment that merges human visual perception with structured wavefronts and optical states that are nonseparable in polarization and spatial modes of light. We demonstrate that humans are able to discriminate between two polarization-coupled orbital angular momentum states with a high probability when directly viewing a structured light beam. The work brings the techniques of structured light to visual science applications and paves the way for methods of characterizing the structure of the macula and conducting experiments with human detectors and optical states with nonseparable modes.

We predict and experimentally verify an entoptic phenomenon through which humans are able to perceive and discriminate optical spin–orbit states. Direct perception and discrimination of these particular states of light with polarization-coupled spatial modes is possible through the observation of distinct profiles induced by the interaction between polarization topologies and the radially symmetric dichroic elements that are centered on the foveola in the macula of the human eye. A psychophysical study was conducted where optical states with a superposition of right and left circular polarization coupled to two different orbital angular momentum (OAM) values (ℓ1 and ℓ2) were directed onto the retina of participants. The number of azimuthal fringes that a human sees when viewing the spin–orbit states is shown to be equal to the number (N) of radial lines in the corresponding polarization profile of the beam, where N=|(ℓ1−ℓ2)−2|. The participants were able to correctly discriminate between two states carrying OAM =7 and differentiated by N=5 and N=9, with an average success probability of 77.6% (average sensitivity d′=1.7, t(9)=5.9, p=2×10−4). These results enable methods of robustly characterizing the structure of the macula, probing retina signaling pathways, and conducting experiments with human detectors and optical states with nonseparable modes.

Propagation of Rectangular Multi-Gaussian Schell-Model Array Beams through Free Space and Non-Kolmogorov Turbulence

In this paper, rectangular multi-Gaussian Schell-model (MGSM) array beams, which consists N×D beams in rectangular symmetry, are first introduced. The analytical expressions of MGSM array beams propagating through free space and non-Kolmogorov turbulence are derived. The propagation properties, such as normalized average intensity and effective beam sizes of MGSM array beams are investigated and analyzed. It is found that the propagation properties of MGSM array beams depend on the parameters of the MGSM source and turbulence. It can also be seen that the beam size of Gaussian beams translated by MGSM array beams will become larger as the total number of terms, M, increases or coherence length, σ , decreases, and the beam in stronger non-Kolmogorov turbulence (larger α and l 0 , or smaller L 0 ) will also have a larger beam size.

Generation and detection of spin-orbit coupled neutron beams

Spin-orbit coupling of light has come to the fore in nanooptics and plasmonics, and is a key ingredient of topological photonics and chiral quantum optics. We demonstrate a basic tool for incorporating analogous effects into neutron optics: the generation and detection of neutron beams with coupled spin and orbital angular momentum. The 3He neutron spin filters are used in conjunction with specifically oriented triangular coils to prepare neutron beams with lattices of spin-orbit correlations, as demonstrated by their spin-dependent intensity profiles. These correlations can be tailored to particular applications, such as neutron studies of topological materials.

Generation of propagation-invariant vector beams with square array by use of 2D binary phase mask and pentagonal prism

In this paper, we realize the generation of propagation-invariant vector beams with square array by use of a 2D binary phase mask and pentagonal prism in a typical Mach-Zehnder optical system. The binary phase mask set in the optical system is perpendicular to the optical axis, and its periodic orientation is 45° relative to the horizontal and vertical directions. One polarizer was used to produce the linearly polarized beam with the angle of 45° relative to the horizontal and vertical directions. One mirror in the Mach-Zehnder optical system was replaced by a pentagonal prism, as the light will be reflected twice inside the pentagonal prism. The intensity distribution of the two branches with the mirror and pentagonal prism have mirror symmetry, and the output optical field of the two branches has an orthogonal polarization state. By adjusting the position of the phase plate accordingly, the total optical field of the two branches can form a vector beam with a square array. The experimental results coincide with the simulation results very well and demonstrate the feasibility of this method.

Self-steering partially coherent vector beams

We introduce a class of self-steering partially coherent vector optical beams with the aid of a generalized complex Gaussian representation. We show that such partially coherent vector beams have mobile guiding centers of their intensity and polarization state distributions on the beam free space propagation that could be employed to generate far-field polarization arrays. Further, we introduce theoretically and realize experimentally a class of vector beams with inhomogeneous statistical and nontrivial far-field angular distributions, which we term cylindrically correlated partially coherent (CCPC) vector beams. We find that such novel beams possess, in general, cylindrically polarized, far-field patterns of an adjustable degree of polarization. The steering control of the intensity and polarization of the self-steering CCPC vector beam is also demonstrated in experiment. Our findings can find important applications, such as trapping of neutral microparticles and excitation of novel surface waves.

High-Efficiency Dual-Frequency Reflective Linear Polarization Converter Based on Metasurface for Microwave Bands

A dual-broadband and high-efficiency reflective linear polarization converter based on an anisotropic metasurface is presented. The device consists of two symmetrical, double-slotted metallic split-rings and one criss-cross structure, a dielectric layer, and a completely reflective metallic ground. The converter exhibits four resonances and can near-perfectly convert x- or y-polarized incident waves into cross-polarized waves in the frequency ranges of 9.38–13.36 GHz and 14.84–20.36 GHz. The polarization conversion ratios (PCRs) of the two bands are 98.21% and 99.32%, respectively. The energy conversion ratio (ECR) for energy loss measurement is almost 100% in these frequency bands. The polarization conversion principle is studied. The bandwidths and PCRs of the two bands are determined by varying the dielectric layer thickness. The simulation results are consistent with experimental observations. The designed dual-broadband and high-efficiency metasurface has great potential in the application of electromagnetic polarization control.

Simultaneous Generation of Complex Structured Curve Beam

At present, people are using holographic technologies to shape complex optical beams for both fundamental research and practical applications. However, most of the reported works are focusing on the generation of a single beam pattern based on the computer-generated hologram (CGH). In this paper, we present a method for simultaneously shaping the multiple beam lattice where the intensity and phase of each individual beam can be prescribed along an arbitrary geometric curve. The CGH that is responsible for each individual beam is calculated by using the holographic beam shaping technique, afterwards all the CGHs are multiplexed and encoded into one phase-only hologram by adding respective linear phase grating such that different curves are appeared in different positions of the focal regions. We experimentally prove that the simultaneous generation of multiple beams can be readily achieved. The generated beams are especially useful for applications such as multitasking micro-machining and optical trapping.