Incident Polarization State Research Articles

Resonant Scattering of Plane‐Wave and Twisted Photons at the Gamma Factory

AbstractA theoretical investigation of the resonant elastic scattering of laser photons by ultra‐relativistic partially stripped ions, that is the core process of the Gamma Factory project, is presented. Special emphasis in the study is placed on the angular distribution and polarization of scattered photons as observed in the collider and ion‐rest reference frames. In order to describe these (angular and polarization) properties for arbitrary relativistic many‐electron ion, the general approach, based on the application of irreducible polarization tensors, is laid down. By making use of the polarization tensors, the scattering of both conventional plane‐wave‐ and twisted (or vortex) photons is explored in detail. For the former case, it is shown how the propagation directions and polarization states of incident and outgoing photons are related to each other for the , , and resonant transitions. For the scattering of initially twisted light that carries non‐zero orbital angular momentum, the angular distribution of secondary photons is explored and the conditions under which they are also twisted are discussed.

Design of on-chip polarimetry with Stokes-determined silicon photonic circuits.

Measuring the states of optical polarization is crucial in many scientific and technological disciplines, and more recently towards the development of chip-scale or nanoscale polarimetry. Here we present a new design of on-chip Stokes polarimetric scheme based on polarization-dependent silicon photonic circuits. The structural elements including polarization rotator and splitter, directional coupler, and phase shifter are assembled to produce polarization-dependent silicon photonic circuits. The orthogonally linear, diagonal, and circular polarization components of the incident light, corresponding to the three Stokes parameters (S1, S2, and S3), can be simultaneously measured based on the Stokes-determined silicon photonic circuit output arrays so as to realize the full measurement of the incident polarization states. This on-chip polarimetry proposed here may enrich the family of micro-nano polarimetric devices, and pave the way to polarization-based integrated optoelectronics, nanophotonics, and metrology.

Statistical Mueller matrix driven discrimination of suspended particles.

An effective method to calculate the statistical Mueller matrix (SMM) of suspended particles based on polarized light scattering is presented that takes advantage of the Stokes vectors measurement of individual particles. The calculation method of the SMM is derived based on statistics. Experimental results of Microcystis samples confirm that the SMM can characterize cells of different states. Then, pairwise contrast experiments indicate the great prospect of the SMM applied on the discrimination of suspended particles. It helps to find the optimal incident polarization state to discriminate suspended particles, and it has optimal discrimination ability. The parameter derived from the SMM can simultaneously discriminate particles including microalgae, microplastics, and sand-like particles.

Polarization evolution on the higher-order Poincaré sphere via photonic Dirac points

In this work, we report a general reflection model to describe the reflected behaviors of a Gaussian beam near photonic Dirac point at the optical interface. With spin polarized electromagnetic waves strikes near the single Dirac point on Dirac material interface, vortical phase distribution and spin inversion are demonstrated for reflected state, and we further develop a higher-order Poincar\'e sphere to describe the evolution of polarization states. It is possible to generate any desired Poincar\'e vortex beam on the sphere by modulating the incident polarization state of light. Moreover, we discuss the case of normal incidence around two adjacent Dirac points, reflection spectrum involves a couple of spin flip vortices corresponding to two points with the corresponding topological invariants, which are consistent with the Berry curvature and topological charge. These results can be extended to similar hyperbolic metamaterials with degenerate point, and inspire a different perspective for manipulating polarized vortex beam with photonic Dirac point.

Spin Hall Effect: Spin Hall Effect under Arbitrarily Polarized or Unpolarized Light (Laser Photonics Rev. 15(7)/2021)

In article number 2100138, Minkyung Kim, Dasol Lee, and Junsuk Rho propose an approach towards the spin Hall effect of light that is independent of the incident polarization state. A symmetrical splitting of an incident light into two circularly polarized light is demonstrated under arbitrarily polarized light and unpolarized light when the two linear polarization states have the same reflection coefficient. The polarization-independent spin Hall effect of light will widen the applicability of the spin-dependent optical devices to cover randomly polarized or unpolarized sources.

Cubic-Phase Metasurface for Three-Dimensional Optical Manipulation.

The optical tweezer is one of the important techniques for contactless manipulation in biological research to control the motion of tiny objects. For three-dimensional (3D) optical manipulation, shaped light beams have been widely used. Typically, spatial light modulators are used for shaping light fields. However, they suffer from bulky size, narrow operational bandwidth, and limitations of incident polarization states. Here, a cubic-phase dielectric metasurface, composed of GaN circular nanopillars, is designed and fabricated to generate a polarization-independent vertically accelerated two-dimensional (2D) Airy beam in the visible region. The distinctive propagation characteristics of a vertically accelerated 2D Airy beam, including non-diffraction, self-acceleration, and self-healing, are experimentally demonstrated. An optical manipulation system equipped with a cubic-phase metasurface is designed to perform 3D manipulation of microscale particles. Due to the high-intensity gradients and the reciprocal propagation trajectory of Airy beams, particles can be laterally shifted and guided along the axial direction. In addition, the performance of optical trapping is quantitatively evaluated by experimentally measured trapping stiffness. Our metasurface has great potential to shape light for compact systems in the field of physics and biological applications.

Metasurface-assisted broadband optical absorption in ultrathin perovskite films.

Ultrathin hybrid organic-inorganic perovskite (HOIP) films have significant potential for use in integrated high-performance photoelectric devices. However, the relatively low optical absorption capabilities of thinner films, particularly in the long-wavelength region, pose a significant challenge to the further improvement of photoelectrical conversion in ultrathin HOIP films. To address this problem, we propose a combining of ultrathin HOIP film with plasmonic metasurface to enhance the absorption of the film effectively. The metasurface excites localized surface plasmon resonances and deflects the reflected light within the HOIP film, resulting in an obvious enhancement of film absorption. Finite-difference time-domain simulation results reveal that the far-field intensities, deflection angles, and electric field distributions can be effectively varied by using metasurfaces with different arrangements. Examination of the reflection and absorption spectra reveals that embedding a specifically designed metasurface into the HOIP film produces an obvious enhancement in broadband optical absorption compared with pure HOIP films. We further demonstrate that this broadband absorption promotion mechanism can be effective at a wide range of HOIP film thicknesses. Comparison of the absorption spectra at various incidence angles of ultrathin HOIP films with and without underlying metasurfaces indicates that the addition of a metasurface can effectively promote absorption under wide-angle incident light illumination. Moreover, by extending the metasurface structure to a two-dimensional case, absorption enhancements insensitive to the incident polarization states have also been demonstrated. This proposed metasurface-assisted absorption enhancement method could be applied in designing novel high-performance thin-film solar cells and photodetectors.

Ultra-broadband solar light wave trapping by gradient cavity-thin-film metasurface

Despite the fact that solar energy has been widely used as a renewable and clean energy source for decades, when designing solar irradiation absorbers one is generally confronted with the dilemma of choosing between higher absorption but narrowband or broadband but lower absorption, which has greatly limited the development of the solar energy industry. In this work, a gradient cavity-thin-film metasurface (GCM) made up of alternating multiple layers of titanium (Ti) and silicon dioxide (SiO2) exhibits ultra-broadband strong absorption in 354–2980 nm. The operating bandwidth covers the dominating portion of the solar irradiation spectrum. The absorption spectrum can be manipulated by adjusting the structural parameters of the unit cell. It is worth noting that the spectrally weighted solar absorption efficiency reaches 98.28% under the AM 1.5G illumination. This impressive near-unity absorption could be attributed to multiple light–matter interactions including surface plasmon resonances, cavity resonance, and the intrinsic spectral responses of multi-layer refractory material. In addition, the absorption response is insensitive to the incident angle and polarization states. These high performances provide the GCM with great potential for practical applications in solar thermal energy harvesting and photothermal conversion, etc.

Thermal lens astigmatism in glass and in cubic crystals with [001] orientation.

The thermal lens was investigated in CaF2 and Tb3Ga5O12 cubic crystals with [001] crystallographic axes orientation and in magneto-optical glass MOG103 by the method of phase-shifting interferometry. It was demonstrated experimentally that the thermal lens has astigmatism determined by the incident radiation polarization state and by the optical anisotropy parameter ξ. A method of ξ determination by measuring thermal lens astigmatism in cubic crystals with [001] orientation was proposed and verified. It was shown that thermally induced depolarization and the amplitude of phase astigmatism depend on the position of the crystal with [001] orientation in antiphase.

Aberration-corrected three-dimensional positioning with a single-shot metalens array

Three-dimensional (3D) positioning with the correction of imaging aberrations in the photonic platform remains challenging. Here, we combine techniques from nanophotonics and machine vision to significantly improve the imaging and positioning performance. We use a titanium dioxide metalens array operating in the visible region to realize multipole imaging and introduce a cross-correlation-based gradient descent algorithm to analyze the intensity distribution in the image plane. This corrects the monochromatic aberrations to improve the imaging quality. Analysis of the two-dimensional aberration-corrected information in the image plane enables the 3D coordinates of the object to be determined with a measured relative accuracy of 0.60%–1.31%. We also demonstrate the effectiveness of the metalens array for arbitrary incident polarization states. Our approach is single-shot, compact, aberration-corrected, polarization-insensitive, and paves the way for future integrated photonic robotic vision systems and intelligent sensing platforms that are feasible on the submillimeter scale, such as face recognition, autonomous vehicles, microrobots, and wearable intelligent devices.

Linear and Nonlinear Polarization Syntheses and Their Programmable Controls based on Anisotropic Time‐Domain Digital Coding Metasurface

Spatial polarization converter can shift the polarization state of incident wave to another state in a specific frequency band. The traditional polarization conversion devices mainly include natural materials and artificial electromagnetic (EM) structures, which are generally sensitive to the incident polarization states and cannot realize polarization manipulations of nonlinear harmonics. These drawbacks limit their developments in wireless communications and radar detection applications. Herein, a general polarization regulation scheme based on anisotropic time‐domain digital coding metasurface is proposed that can achieve both linear and nonlinear polarization syntheses and realize their programmable controls in real time. In this scheme, a nonlinear modulation theory into the polarization conversion methods is integrated, and thus, the scope of the polarization regulation is expanded. An anisotropic time‐domain digital coding metasurface is designed and fabricated to validate the feasibility of the proposed scheme. Theoretical predictions have good agreements with the experiments. The results of this study are expected to promote the developments of space‐time‐polarization regulations and provide efficient approaches for precise EM detections.

Dynamical characteristics of Laguerre–Gaussian vortex beams upon reflection and refraction

Laguerre–Gaussian beams with vortex structure, as a special type of electromagnetic wave, can carry energy, momentum, and angular momentum, which is crucial for understanding of dynamical processes concerning light–matter interaction phenomena. In this paper, we theoretically investigate the local dynamical characteristics of Laguerre–Gaussian vortex beams upon reflection and refraction. Using a hybrid method based on the angular spectrum representation and vector potential in the Lorenz gauge, the explicit analytical expressions for the electric and magnetic field components of reflected and refracted Laguerre–Gaussian beams are derived in the form of a Hermite polynomial. A canonical approach is utilized to examine the energy, momentum, and spin and orbital angular momentum of the Laguerre–Gaussian vortex beams’ reflection and refraction at a plane interface between air and BK7 glass. The effects of the incidence angle, topological charge, and polarization state on these dynamical quantities are simulated and discussed in detail. This study may provide useful insights into the interactions of vortex beams with matter and their further applications.

Solar Selective Absorbers for High-efficiency Photothermal Conversion via Core–Shell Nanocone Structured Surface

Nanostructured surface, a promising photon management strategy, enables to enhance photon-to-heat conversion efficiency by manipulating spectral radiative properties ranging from solar spectrum (0.3–2.5 μm) to mid-infrared spectrum (2.5–20 μm). Here, a core–shell nanocone structured surface made of silica core and tungsten shell as a solar selective absorber is introduced. The photothermal conversion efficiency (PTCE) is calculated in consideration of solar spectrum absorption and mid-infrared emission. It is obvious that high solar spectrum absorption and low mid-infrared emission are beneficial for high PTCE. The influence of structural parameters on the PTCE is studied, and then the absorption enhancement mechanism is elucidated in detail. Meanwhile, the influences of incident angle, polarized state, and lattice arrangement are also presented. The calculated results exhibit that our optimized solar absorber possesses the total solar absorption of 97.3% and total thermal emission of 7.6%, resulting in a maximum PTCE of 91.4% under one sun illumination conditions at normal incidence. Moreover, our solar selective absorber is independent to the incident angle and polarization state. The excellent photothermal conversion performance with wide-angle and polarization-insensitive properties for the solar selective absorber can serve as a good candidate for various solar thermal applications including seawater desalination, steam generation, thermophotovoltaic, and photocatalysis.

Melanin concentration and depolarization metrics measurement by polarization-sensitive optical coherence tomography

Imaging of melanin in the eye is important as the melanin is structurally associated with some ocular diseases, such as age-related macular degeneration. Although optical coherence tomography (OCT) cannot distinguish tissues containing the melanin from other tissues intrinsically, polarization-sensitive OCT (PS-OCT) can detect the melanin through spatial depolarization of the backscattered light from the melanin granules. Entropy is one of the depolarization metrics that can be used to detect malanin granules in PS-OCT and valuable quantitative information on ocular tissue abnormalities can be retrived by correlating entropy with the melanin concentration. In this study, we investigate a relationship between the melanin concentration and some depolarization metrics including the entropy, and show that the entropy is linearly proportional to the melanin concentration in double logarithmic scale when noise bias is corrected for the entropy. In addition, we also confirm that the entropy does not depend on the incident state of polarization using the experimental data, which is one of important attributes that depolarization metrics should have. The dependence on the incident state of polarization is also analyzed for other depolarization metrics.

Optimal configurations for different incident polarization states in linear polarization calibration.

The purpose of polarization calibration is to measure the response matrix of an instrument and the deviation of noise to correct for subsequent flight measurements. The precision, however, is relative to the states of incident light. We investigate the influence of partially polarized light, in the presence of signal-independent additive noise or signal-dependent Poisson shot noise. We obtain the estimation precision for different numbers of the polarization state generators and analyzers in linear Stokes measurements. To reduce the influence of incident light, we suggest that the numbers of the polarization state generators and analyzers should be greater than or equal to 4. In particular, for an instrument including three polarizers oriented at 0°, 60°, and 120°, estimation precision is found to be dependent on the response matrix and incident polarization states.

Polarization-sensitive subtractive structural color used for information encoding and dynamic display

Structural color with polarization sensitivity has been widely studied due to its benefits for improving information storage and dynamic color display capacity. However, large amount and good concealment of information encoding are the major issues to be addressed. Here, we propose the elliptical Al/a-Si/Al (metal-insulator-metal, MIM) nanostructure arrays as the basic building blocks to realize polarization-sensitive subtractive structural colors for information encoding, and dynamic polarization-resolved displays. The experimentally realized structural color exhibits a wide color gamut covering the whole cyan, magenta, and yellow (CMY) color system, and presents a strong dependence on the incident polarization state due to its shape anisotropy. A new approach to improve the information encoding capacity is demonstrated using this structure combined with the polarization-independent nanostructures, increasing the concealment of information. Additionally, the polarization controllable dynamic display is engineered by the well-designed pixels with respect to different polarizations, generating the animation effect. These intrinsic properties and functionalities of the proposed structural color significantly extend its potential to the fields of information encoding, security encryption, and dynamic displays, not limited to color printing and filtering devices.

Multi-functional two-dimensional holographic grating based on silver pattern coated by azopolymer

A two-dimensional diffraction device with the properties of polarization modulation, angular sensitivity, polarization-independent diffraction efficiency and repeatable recording has been designed and fabricated in an azopolymer-silver double-layer film by means of two-step holographic exposure. A silver pattern is formed in the light field with the sinusoidally distributed intensity, and then a polarization holographic grating is recorded in the azobenzene liquid-crystalline layer through the interference of two orthogonally linearly polarized lasers. We report here that the polarization states of the diffraction beams from the recorded two-dimensional grating are orthogonally modulated; the diffraction efficiency is related to the incident angle of the probe light and the rotation angle between the two-step recording, while independent on the incident polarization state. Furthermore, the experimental results are analyzed through the scalar diffraction theory and Jones matrices.

Ultra-broadband perfect absorber utilizing a multi-size rectangular structure in the UV-MIR range

We propose an ultra-broadband perfect absorber (UBPA) utilizing a multi-size rectangular structure, which consists of multi-layer silicon/iron (Si/Fe) units. A single-layer model is designed based on the theory of dipole equivalent circuit, and a nine-layer model is demonstrated with the FDTD method. Surprisingly, the absorber shows an average absorptivity of over 96% in the range of 300–3000 nm under the normal incident, which covers from the ultraviolet to mid-infrared (UV-MIR) region. A good tolerance of incident angle and polarization state is proved. It is found that the average level of absorption still exceeds 91% at a larger viewing angle of ±70° under the TM polarization. The excellent absorption performance is revealed by the slow-wave effect, localized surface plasmon resonance (LSPR), and propagating surface plasmons (PSPs). In addition, both chromium and iron films are used in the multi-layer structure to avoid the iron oxidation. Thus, the proposed absorber reduces the cost of actual production and can be applied in many areas, such as solar cells and emitters.

Multi-foci metalens for terahertz polarization detection.

We propose a reflective terahertz (THz) metalens with four focal points for polarization detection of THz beams. The metalens is composed of Z-shaped resonators with spatially variant orientations, a reflective gold layer, and a dielectric spacer between them. The polarization states of the focal points include left circular polarization, right circular polarization, an incident polarization state, and a polarization state whose major axis is rotated π/4 in comparison with that of the incident polarization. The handedness, ellipticity, and major axis of the polarization state can be determined based on the light intensities of the focal points. The uniqueness of the designed device renders this technique very attractive for applications in compact THz polarization detection and information processing.

Origin of the Kerr effect: investigation of solutions by polarization-dependent Z-scan

The nonlinear refractive index dependence on the incident light polarization state has been studied for pure chloroform and chloroform solutions of aminobenziliden-1,3-indandione derivatives. Measurements were done with linearly, elliptically, and circularly polarized light using 8 ns and 30 ps pulse duration 1064 nm lasers. This allows us to separate the electronic response, molecular reorientation, and thermo-optical components of the nonlinear refractive index. The refractive index variations with the change of laser pulse repetition rate were employed to identify the presence of the thermo-optical effect. Quantum chemical calculations of linear polarizability were used to estimate the magnitude of molecular-reorientation-induced refractive index changes for solvents and solutions. Overall, in this paper we have outlined various essential aspects that need to be taken into account to correctly interpret Z-scan measurement results for organic solvents and solutions.