arXiv subjects

Dusan Sarenac

Publications and source records attributed to Dusan Sarenac.

27 records · Page 2Linked to original sources

arXiv2023

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 alter the structure of the macula. Structured light tools enable the direct probing of macular pigment density 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. The perceived size of the entoptic pattern was observed to vary between participants, with an average visual angle threshold radius of $9.5^\circ \pm 0.9^\circ$, 95% C.I. = [$5.8^\circ$, $13^\circ$], in a sample of healthy participants. These results (with eleven azimuthal fringes) differ markedly from previous estimates of the Haidinger's brush phenomenon's extant (two azimuthal fringes), of $3.75^\circ$, suggesting that higher azimuthal fringe density increases pattern visibility. The increase in apparent size and clarity of entoptic phenomenon produced by the presented structured light stimuli may possess greater potential to detect the early signs of macular disease over perception tasks using uniform polarization stimuli.

physics.med-ph↗

arXiv2021

Remote state preparation of single photon orbital angular momentum lattices

Optical beams with periodic lattice structures have broadened the study of structured waves. In the present work, we generate spin-orbit entangled photon states with a lattice structure and use them in a remote state preparation protocol. We sequentially measure spatially-dependent correlation rates with an electron-multiplying intensified CCD camera and verify the successful remote preparation of spin-orbit states by performing pixel-wise quantum state tomography. Control of these novel structured waves in the quantum regime provides a method for quantum sensing and manipulation of periodic structures.

quant-ph↗

arXiv2020

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 $=\pm1$, with an average success probability of $69\%$ ($S.D. = 22\%$, $p = 0.013$). 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.

physics.optics↗

arXiv2020

Talbot Effect of orbital angular momentum lattices with single photons

The self-imaging, or Talbot Effect, that occurs with the propagation of periodically structured waves has enabled several unique applications in optical metrology, image processing, data transmission, and matter-wave interferometry. In this work, we report on the first demonstration of a Talbot Effect with single photons prepared in a lattice of orbital angular momentum (OAM) states. We observe that upon propagation, the wavefronts of the single photons manifest self-imaging whereby the OAM lattice intensity profile is recovered. Furthermore, we show that the intensity at fractional Talbot distances is indicative of a periodic helical phase structure corresponding to a lattice of OAM states. This phenomenon is a powerful addition to the toolbox of orbital angular momentum and spin-orbit techniques that have already enabled many recent developments in quantum optics.

quant-ph↗

arXiv2017

Increased interference fringe visibility from the post fabrication heat treatment of a perfect crystal silicon neutron interferometer

Construction of silicon neutron interferometers requires a perfect crystal silicon ingot (5 cm to 30 cm long) be machined such that Bragg diffracting "blades" protrude from a common base. Leaving the interferometer blades connected to the same base preserves Bragg plane alignment, but if the interferometer contains crystallographic misalignments of greater than about 10 nrad between the blades, interference fringe visibility begins to suffer. Additionally, the parallelism, thickness, and distance between the blades must be machined to micron tolerances. Traditionally, interferometers do not exhibit usable interference fringe visibility until 30 $μ$m to 60 $μ$m of machining surface damage is chemically etched away. However, if too much material is removed, the uneven etch rates across the interferometer cause the shape of the crystal blades to be outside of the required tolerances. As a result, the ultimate interference fringe visibility varies widely among neutron interferometers that are created under similar conditions. We find that annealing a previously etched interferometer at $800^\circ \mathrm{C}$ dramatically increased interference fringe visibility from 23 % to 90 %. The Bragg plane misalignments were also measured before and after annealing using neutron rocking curve interference peaks, showing that Bragg plane alignment was improved across the interferometer after annealing. This suggests that current interferometers with low fringe visibility may be salvageable and that annealing may become an important step in the fabrication process of future neutron interferometers, leading to less need for chemical etching and larger, more exotic neutron interferometers.

physics.ins-det↗

arXiv2016

Decoupling of a Neutron Interferometer from Temperature Gradients

Neutron interferometry enables precision measurements that are typically operated within elaborate, multi-layered facilities which provide substantial shielding from environmental noise. These facilities are necessary to maintain the coherence requirements in a perfect crystal neutron interferometer which is extremely sensitive to local environmental conditions such as temperature gradients across the interferometer, external vibrations, and acoustic waves. The ease of operation and breadth of applications of perfect crystal neutron interferometry would greatly benefit from a mode of operation which relaxes these stringent isolation requirements. Here, the INDEX Collaboration and National Institute of Standards and Technology demonstrates the functionality of a neutron interferometer in vacuum and characterize the use of a compact vacuum chamber enclosure as a means to isolate the interferometer from spatial temperature gradients and time-dependent temperature fluctuations. The vacuum chamber is found to have no depreciable effect on the performance of the interferometer (contrast) while improving system stability, thereby showing that it is feasible to replace large temperature isolation and control systems with a compact vacuum enclosure for perfect crystal neutron interferometry.

physics.ins-det↗

arXiv2016

Spin-Orbit States of Neutron Wavepackets

We propose a method to prepare an entangled spin-orbit state between the spin and the orbital angular momenta of a neutron wavepacket. This spin-orbit state is created by passing neutrons through the center of a quadrupole magnetic field, which provides a coupling between the spin and orbital degrees of freedom. A Ramsey fringe type measurement is suggested as a means of verifying the spin-orbit correlations.

quant-ph↗

arXiv2016

Broadband Neutron Interferometer

We demonstrate a two phase-grating, multi-beam neutron interferometer by using a modified Ronchi setup in a far-field regime. The functionality of the interferometer is based on the universal \moire effect that was recently implemented for X-ray phase-contrast imaging in the far-field regime. Interference fringes were achieved with monochromatic, bichromatic, and polychromatic neutron beams; for both continuous and pulsed beams. This far-field neutron interferometry allows for the utilization of the full neutron flux for precise measurements of potential gradients, and expands neutron phase-contrast imaging techniques to more intense polycromatic neutron beams.

physics.ins-det↗

arXiv2016

Demonstration of a white beam far-field neutron interferometer for spatially resolved small angle neutron scattering

We provide the first demonstration that a neutron far-field interferometer can be employed to measure the microstructure of a sample. The interferometer is based on the moiré pattern of two phase modulating gratings which was previously realized in hard x-ray and visible light experiments. The autocorrelation length of this interferometer, and hence the microstructure length scale that is probed, is proportional to the grating spacing and the neutron wavelength, and can be varied over several orders of magnitude for one pair of gratings. We compare our measurements of the change in visibility from monodisperse samples with calculations which show reasonable agreement. The potential advantages of a far-field neutron interferometer include high fringe visibility in a polychromatic beam (over 30 %), no requirement for an absorbing grating to resolve the interference fringes, and the ability to measure the microstructure in the length scale range of 100 nm to 10 \mum by varying either the grating spacing or neutron wavelength with a broad wavelength range and single set of gratings.

physics.ins-det↗