Polarization Of Incident Beam Research Articles

Incident beamline design for a modern cold triple axis spectrometer at the High Flux Isotope Reactor

A modern cold triple axis spectrometer is being planned for the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Here, we describe the design of an incident beamline that will put a flux of ∼108ncm2s on a sample with an area of 2 cm × 2 cm. It takes current physical constraints at HFIR into account and it can accommodate both single and multiplexed analyzer-detector secondary spectrometers and large superconducting magnets. The proposed incident beamline includes a multi-channel guide with horizontal focusing, a neutron velocity selector, components to facilitate an incident beam polarization option, and a double-focusing pyrolytic graphite monochromator. This work describes the process of optimizing the guide system and monochromator and summarizes the expected performance of the incident beamline for non-polarized operation.

Multi-channel vortex beam based on single layer transmission-type metal metasurface

We design a transmission type flexible metasurface which operates at 0.1 THz. The metasurface consists of a polyimide substrate and a metallic copper film. Using the geometric phase principle, four vortex beams with different channels and different topological charges are generated under the linearly polarized beam incident. Through three-dimensional electromagnetic field simulation and experimental tests, it is proved that the designed metasurface can generate multi-channel vortex beams, where the topological charges of the vortex beam are ± 1 and ± 2. The metasurface has high transmittance in the frequency band of 0.092THz to 0.106THz, 0.202THz to 0.283THz, 0.318THz to 0.345THz, and so on, which can generate multi-channel vortex beams at multiple frequency bands. Metasurfaces designed based on this method can be applied in optical communication.

RDDA method for characterization of photonic nanojets.

This paper presents a reduced discrete dipole approximation (RDDA) method as a flexible and powerful tool for computing the field distribution of photonic nanojets (PNJs) based on superposition of the induced dipole radiation fields with a low number of lattice points at the surface of microparticles. Microparticles with spherical and ellipsoidal shapes have been studied using the RDDA method to produce PNJs. The incident beam polarization and filling factor effects in the PNJs' shape and confinement strength have been characterized by quality factor Q. The best confined PNJs have been found in microellipsoids with a specific range of the shape parameter and filling factor values.

Monolayer Chiral Metasurface for Generation of Arbitrary Cylindrical Vector Beams

The cylindrical vector beam (CVB) has been widely studied and applied in recent years. However, many CVB generation methods suffer from complex systems, and large-size devices are required. Here, we propose a monolayer chiral metasurface composed of spin-sensitive unit cells which can generate different holograms for left- and right-circular polarization based on the combined modulation of geometric phase and detour phase. With a linearly polarized incident beam, the metasurface can generate CVBs with controllable polarization angles and orders, and even more complex vector beams. This work provides a new idea for the design of miniaturized optical devices for generating arbitrary vector beams.

Measurement of surface chirality at near-normal incidence

The chirality of a medium is typically measured either by transmitting a beam of light through it or by single or multiple interface reflection at large and/or special angles of incidence. We propose and demonstrate here the experimental measurement of surface chirality of z-cut quartz crystal by reflecting a focused beam of light at a near-normal angle of incidence. A small difference in the reflection coefficients between orthogonal elliptically polarized incident beam of 10−4 is measured in the dark-field region of the reflected light via the weak measurement method, taking advantage of the significant transverse spin-shift (TSS) that arises due to the interaction. The TSS behavior is simulated for different chiral parameters (±γ) of the material. The experimental results match well with the theoretically simulated behavior to quantify γ of quartz crystal used as an example interface. The significance of our method can be of interest for a wide variety of fundamental and applied investigations.

Thermally tunable vanadium-dioxide-based broadband metamaterial absorber with switchable functionality in the terahertz band

In this paper, a thermally tunable broadband metamaterial absorber, with switchable functionality in the terahertz band, consisted of periodically arranged vanadium dioxide (VO2) and a gold film separated by a layer of polyimide is reported, which is capable of switching from absorber to reflector through the phase change property of VO2. When VO2 is in the metallic state, three near-perfect absorption peaks localized at 3.48 THz, 5.09 THz and 7.05 THz are obtained, and the combination of them gives rise to a broadband absorption, more than 90% of absolute absorption bandwidth reaches 4.35 THz (3.1–7.45 THz) with a relative absorption bandwidth of 82.46%. When VO2 is in the dielectric state, it can switch from near-perfect broadband absorption to near-perfect reflection with the maximum intensity modulation of 92.4%. The broadband absorption is insensitive to polarization of incident beam due to symmetrical structure design and exhibits excellent tolerance for large oblique incidence angle. In addition, size changes of patterned VO2 array structure provides a large impact on the absorption performance of the thermally tunable device, especially the absorption bandwidth. Our proposed device is expected to have outstanding prospects in terahertz thermal imaging, communications, and temperature-controlled metasurface.

Single-shot quantitative amplitude and phase imaging based on a pair of all-dielectric metasurfaces

Quantitative amplitude and phase imaging (QAPI) has been an effective technique to examine label-free biomedical samples. Simple and reliable QAPI techniques realized by replacing conventional bulky optical elements with planar structures will improve the system portability and facilitate in vivo imaging applications. Here, we propose a single-shot QAPI method realized by simply inserting a pair of all-dielectric geometric phase metasurfaces into a traditional microscope. The first metasurface splits a linearly polarized incident beam into two circularly polarized components and the following metasurface deflects the two beams back toward their initial directions. The metasurface pair generates two laterally displaced replicas of the input object, of which the interference forms a retardance image with a bias retardation controlled by an analyzer. The amplitude and phase information of the object is reconstructed from four retardance images simultaneously recorded by a polarized camera. The metasurface pair can be placed near any conjugate plane of the object, which provides a flexible and robust configuration for QAPI, demonstrating its wide usage in live imaging.

Plasmonic spin induced Imbert–Fedorov shift

Abstract The spin angular momentums of surface plasmon polaritons (SPPs) on chiral material interfaces and the Imbert–Fedorov shifts of linearly polarized light beams are investigated. Compared to a traditional TM-polarized SPP having a transverse spin, the SPP on a chiral material interface also has a longitudinal spin component, resulting from the nature that this new kind of SPP is a hybrid of TE and TM-polarized evanescent waves. When a light beam is incident on a sandwich structure composed of chiral material, prisms, and metal layers, in which the SPP is supported, the reflection and transmission processes can be analogous to the transport of a photon in a waveguide QED system. The SPP with longitudinal spin can be excited by the incident wave and the reflected and transmitted beams carry the spin features of the SPP. Moreover, the beams exhibit large Imbert–Fedorov shifts stemming from the spin–orbit coupling even for a linearly polarized incident beam. The shifts are determined by the longitudinal spin angular momentum and excitation coefficient of the SPP. This present work extends the study of photonic spin–orbit coupling and provides an important platform to investigate the plasmonic spin.

Optical vortex beam controlling based on fork grating stored in a dye-doped liquid crystal cell.

In this paper, we investigate the generation and controlling of the optical vortex beam using a dye-doped liquid crystal (DDLC) cell. The spatial distribution of the quasi-sinusoidal orientation of the liquid crystal molecules creates a quasi-sinusoidal phase grating (PG) in the DDLC cell. Depending on the incident light pattern, Trans to Cis photoisomerization of the dye molecules affects the orientation of the liquid crystal molecules. To do so, an amplitude fork grating (FG) is used as a mask, and its pattern is stored in the cell by a pattern printing method as the PG. One of the particular features of the stored grating in the cell is its capability in the diffraction efficiency controlled by the applied electric field. The results show, based on the central defect in the FG pattern, the diffracted probe beam in different orders is optical vortices. As a new technique, this type of stored pattern acts like an amplitude grating but according to the results, its structure is in fact a PG. This technique leads to the vortex beam switching capability by applying an electric field to the cell. The results show that by applying 22V, all the diffraction orders vanish. Meanwhile, the vortex beams reappear by removing the applied voltage. The diffraction efficiency of the vortex beams as well as its generation dependency on the polarization of the incident beam studied. The maximum efficiency of the first diffraction order for linear polarized incident beam was obtained at 0V, about 8%. Based on the presented theory, a simulation has been done which shows the Cis form of the dye molecules has been able to change the angle of LC molecules on average about 12.7°. The study of diffracted beam profiles proves that they are electrically controllable vortex beams.

Enhancing terahertz photonic spin Hall effect via optical Tamm state and the sensing application

The photonic spin Hall effect (PSHE), characterized by two splitting beams with opposite spins, has great potential applications in nano-photonic devices, optical sensing fields, and precision metrology. We present the significant enhancement of terahertz (THz) PSHE by taking advantage of the optical Tamm state (OTS) in InSb-distributed Bragg reflector (DBR) structure. The spin shift of reflected light can be dynamically tuned by the structural parameters (e.g. the thickness) of the InSb-DBR structure as well as the temperature, and the maximum spin shift for a horizontally polarized incident beam at 1.1 THz can reach up to 11.15 mm. Moreover, we propose a THz gas sensing device based on the enhanced PSHE via the strong excitation of OTS for the InSb-DBR structure with a superior intensity sensitivity of 5.873 × 104 mm/RIU and good stability. This sensor exhibits two orders of magnitude improvement compared with the similar PSHE sensor based on InSb-supported THz long-range surface plasmon resonance. These findings may provide an alternative way for the enhanced PSHE and offer the opportunity for developing new optical sensing devices.

Coordinate-transformation iteration algorithm for phase modulation of arbitrary axial light distribution.

Axial light distribution modulation is widely applied in optical tweezers, hard-brittle material cutting, multilayer laser direct writing, etc. To generate arbitrary axial light distribution, the coordinate-transformation iteration (CTI) algorithm is presented. The CTI algorithm unifies equations in low and high numerical aperture (NA) scenarios, using the same iterative algorithm to produce phase computer-generated holograms. In a low NA scenario, twin-foci, flattop, and sin2 distributions have been achieved. In high NA scenarios, multirings, multifoci, and needle-like distributions have been realized in simulation with specific polarized incident beams. Since the CTI algorithm is inherently an efficient one-dimensional phase retrieval algorithm that is not limited by NA, this method has the potential to become a well-received solution for axial light distribution modulation.

Sub-diffraction focusing by a meta spiral zone plate

The sub-diffraction focus has been widely studied because of its wide application in the fields of optical lithography and super-resolution imaging. The methods based on the traditional refractive elements to achieve sub-diffraction focal spots face the problem of large volume, large mass and difficult alignment. Although diffractive optical elements can achieve the combination of multiple phase modulation functions, the polarization modulation cannot be achieved by such elements. As a planar element to achieve integrated modulation of phase and polarization, the metasurface has the potential to further miniaturize the sub-diffraction focusing system and eliminate alignment errors. In this article, we demonstrate the meta spiral zone plate, which converts the incident linearly polarized beam to an azimuthally polarized beam and focuses the latter into a sub-diffraction solid spot. The meta spiral zone plate with a diameter of 600 μm and a numerical aperture of 0.8 working at the wavelength 405 nm is designed and verified experimentally. The simulated full width at half maximum (FWHM) and measured FWHM of the focus spot are 0.6λ and 0.65λ. The simulated and measured efficiencies are 37.69% and 15.18%, respectively. Meanwhile, the effects of the incident beam's incident angle and polarization orientation on the focal spot are also investigated. Our proposal eliminates the alignment errors in the traditional methods and further simplifies the optical systems realizing sub-diffraction focusing, which may have great potential applications in super-resolution focusing and optical manipulation.

Polarized Radiative Transfer Simulations: A Tutorial Review and Upgrades of the Vector Discrete Ordinate Radiative Transfer Computational Tool

We present an overview and several important upgrades to the Vector Discrete Ordinate Radiative Transfer (VDISORT) code. VDISORT is a polarized (vector) radiative transfer code that can be applied to a wide range of research problems including the Earth’s atmosphere and ocean system. First, a solution is developed to the complex algebraic eigenvalue problem resulting when the b2 component of the Stokes scattering matrix is non-zero. This solution is needed to compute the V component of the Stokes vector I=[I∥,I⊥,U,V]T. Second, a significant improvement in computational efficiency is obtained by reducing the dimension of the algebraic eigenvalue by a factor of 2 resulting in a speed increase of about 23 = 8. Third, an important upgrade of the VDISORT code is obtained by developing and implementing a method to enable output at arbitrary polar angles by the integration of the source function (ISF) method for partially reflecting Lambertian as well as general non-Lambertian surfaces. Fourth, a pseudo-spherical treatment has been implemented to provide important corrections for Earth curvature effects at near horizontal solar zenith and observation (viewing) polar angles. Fifth, a post-processing single-scattering correction procedure has been developed to enhance the accuracy and speed for strongly forward-peaked scattering. With these significant improvements the results from the upgraded version of the VDISORT code match published benchmark results for Rayleigh scattering, Mie scattering, and scattering by non-spherical cirrus particles. The performance of VDISORT for a polarized incident beam source is equally satisfactory. The VDISORT vector radiative transfer code is made public and freely available for use by the growing polarimetric research community including the space-borne polarimeters on the future NASA PACE and AOS missions.

Enhanced photonic spin Hall effect of reflected light from a doubly linear gradient-refractive-index material.

The photonic spin Hall effect (SHE), manifesting itself as spin-dependent splitting of light, holds potential applications in nano-photonic devices and precision metrology. However, the photonic SHE is generally weak, and therefore its enhancement is of great significance. In this paper, we propose a simple method for enhancing the photonic SHE of reflected light by taking advantage of the gradient-refractive-index (GRIN) material. The transverse shifts for a normal (homogeneous) layer and linear GRIN structure with three different types (singly increasing, singly decreasing, and doubly linear ones) are theoretically investigated. We found that the doubly linear GRIN materials exhibit the prominent photonic SHE of reflected light, which is mainly due to the Fabry-Perot resonance. By optimizing the thickness and the lower (higher) refractive index of the doubly linear GRIN layer, the transverse shift for a horizontally polarized incident beam can nearly reach its upper limitation (i.e., half of the beam waist). These findings provide us a potential method to enhance the photonic SHE, and therefore establish a strong foundation for developing spin-based photonic devices in the future.

Measurement of polarization transfer in Møller scattering of relativistic electrons

A dedicated Mott polarimeter was designed to study the final spin state in M\o{}ller scattering of transversely polarized electron beams in the relativistic energy range. The polarization transfer was measured for two incident-beam polarization orientations with respect to the M\o{}ller scattering plane, at 3 MeV incident-beam energy. The results are found to be in agreement with the predictions of relativistic quantum mechanics. Estimates for the measurement of quantum spin correlations in M\o{}ller scattering, based on a simultaneous determination of the spin projections for both electrons in the final state, are also presented.

Interfacial anisotropic exciton-polariton manifolds in ReS2

Light–matter coupling in van der Waal’s materials holds significant promise in realizing bosonic condensation and superfluidity. The underlying semiconductor’s crystal asymmetry, if any, can be utilized to form anisotropic half-light half-matter quasiparticles. We demonstrate generation of such highly anisotropic exciton-polaritons at the interface of a biaxial layered semiconductor, stacked on top of a distributed Bragg reflector. The spatially confined photonic mode in this geometry couples with polarized excitons and their Rydberg states, creating a system of highly anisotropic polariton manifolds, displaying Rabi splitting of up to 68 meV. Rotation of the incident beam polarization is used to tune coupling strength and smoothly switch regimes from weak to strong coupling, while also enabling transition from one three-body coupled oscillator system to another. Light–matter coupling is further tunable by varying the number of weakly coupled optically active layers. Our work provides a versatile method of engineering devices for applications in polarization-controlled polaritonics and optoelectronics.

Polarization modulation by surface plasmons in Young's double-slit setup

A simple phenomenological model, justified by rigorous electromagnetic analysis, is used to examine far-field polarization modulation introduced by a metallic screen with two subwavelength slits in uniform, partially polarized illumination. The accuracy of this intuitive model is assessed numerically, by employing the Fourier modal method, as regards the wavelength, the screen metal, and the slit depth, width, and separation. The Stokes parameters and the degree of polarization are evaluated paraxially in the far zone of the slits. We demonstrate that a uniform, partially linearly polarized incident beam can be rendered unpolarized by the nanoslits. Our work provides insight into the pivotal role that surface plasmons have in polarization modulation in photonics.

Structured Light Control and Diagnostics Using Optical Crystals

We describe experimental results exposing the possibilities of optical crystals, especially anisotropic and birefringent, for creation, control, and diagnostics of structured light fields with singular and extraordinary properties. The efficiency of birefringent media is demonstrated for purposeful generation of optical beams with phase singularities (optical vortices) and desirable patterns of internal energy flows, in both the mono- and polychromatic light. On the other hand, anisotropic micro-objects can be used as probing bodies for investigation of the peculiar features of internal energy flows and corresponding momentum and angular momentum distributions in structured light fields. In particular, the specific mechanical action of light fields, formed under the total-reflection conditions, has been detected that confirms the existence of “extraordinary” dynamical characteristics of evanescent light waves predicted theoretically: the “transverse” momentum and “vertical” spin and their dependence on the incident beam polarization. The results can be useful for the optical trapping and micromanipulation techniques, including the biomedical and pharmaceutical applications.

Spatial shifts of the reflective light beam off the metasurface of hyperbolic crystals

We investigated Goos–Hänchen (GH) and Imbert–Fedorov (IF) shifts of the reflective beam from a uniaxial hyperbolic crystal (HC) with a metasurface (MS) that is a subwavelength rectangular-grating layer. Due to the optical axis of this MS normal to that of the HC, this structure is similar to a biaxial HC for the reflective beam. We obtained analytical expressions of reflective beam for any polarized incident light beam and then derived the GH and IF shifts of the relevant reflective beam. Based on the hexagonal boron nitride crystal (hBN), we numerically simulated shift spectra of the reflective beam for differently polarized incident beams. We compared the results obtained from this structure with those for the bulk hBN or MS layer with infinite thickness. We found that the shift spectra from this structure resemble neither those from the bulk hBN nor those from the MS layer so that they are much more complicated than those in the two extreme cases. The effect of the MS coupling with the hBN substrate is very remarkable. First, both the GH and IF shifts are evidently enlarged, especially the IF shift. Second, the shift spectra exhibit oscillation behavior and sharp shift peaks or dips. Finally, the MS brings out the nonreciprocity of the two shifts for the circularly polarized incident beams.

Enhanced and unidirectional photonic spin Hall effect in a plasmonic metasurface with S4 symmetry.

In this Letter, we report the significant enhancement of the photonic spin Hall effect (SHE) in a plasmonic metasurface with ${\rm S}_4$ symmetry. We find that an enhanced SHE of reflected light can occur in both horizontally and vertically polarized incident beams, and the maximum transverse displacement can approach half of the beam waist. Such a large displacement is caused by the non-resonant and near-zero pseudo-Brewster angles in the plasmonic metasurface. Owing to ${\rm S}_4$ symmetry, a unidirectional SHE is obtained in the metasurface, i.e., large and tiny transverse displacements are realized for a linearly polarized beam incident from the opposite side. This Letter provides a new, to the best of our knowledge, way to achieve an enhanced photonic SHE and offers more opportunities for designing spin-based nanophotonic devices.