Reflection Of Polarized Light Research Articles

Creation and plasmon anisotropy spectroscopy of wedge-shaped gold nanoclusters conditioned by GaAs(001) surface

Wedge-shaped nanoclusters of gold (Au2Ga) are fabricated by high-temperature annealing of a gold nanofilm deposited onto (001) surface of p-doped GaAs crystal with a very thin overlayer of natural oxide. The data of diagnostics confirm the presence in prepared Au/p-GaAs(001) structures of the wedge-shaped Au-intermetallic nanoclusters elongated in [110] direction at GaAs surface. A crystallographic model of the wedge-shaped Au (Au2Ga) nanoclusters conditioned by GaAs(001) surface is discussed in relation with their physicochemical nature. Anisotropic plasmons localized on equally oriented Au-based nanoclusters are detected optically with the reflectance anisotropy spectroscopy and investigated thoroughly with the spectroscopy of polarized light reflection. It is proved experimentally and theoretically that the inhomogeneously broadened infrared spectral peak at the energy about 1.1 eV is associated with plasmons polarized along the wedge-shaped clusters in [110] crystal direction. Another peak - at the energy approximately of 1.8 eV - is due to plasmons having orthogonal polarization in direction [11¯0].

A confined self-assembly approach towards chiral photonic materials with circularly polarized structural colors for information storage and encryption

Chiroptical materials with tunable circular polarization performances have gained wide interest because of promising applications in optical devices and information communication. However, limited by their intrinsic chirality, such materials suffer from serious deficiencies in dynamical manipulation on circularly polarized light (CPL). Here, we demonstrate a kinetic trapping approach to capture multi-domain cholesteric mesophases for polarization-dependent structural coloration. The resultant photonic structures depicted by limited solvent evaporation display light control from selective left-handed circularly polarized light reflection to dual reflection, as a result of forming highly tilted and distorted domains with a phase-retardation effect. Notably, a positive linear correlation is established between the circular polarization behavior and structural orientation regulated by the solvent evaporation. The tunable circular polarization structural colors enable the application of the photonic materials for complex encryption in terms of polychromatic coding arrays. The confined-anisotropic-fabrication method of photonic structures paves a foundation toward advanced functional materials with promising applications in light science and technology.

Plasmon Resonance Properties of Au, Cu and Ag Multi-layered Structures with P(VDF-TrFE)

The theoretical modeling of the optical response of layered metal-polymer structures, which can be employed as plasmonic sensors, is carried out. The calculation of their linearly polarized light reflection is performed with the use of the well-known matrix method, which describes the electromagnetic radiation propagation through a sequence of homogeneous flat-parallel media layers. In this way, the attenuated total reflection curves of the structures containing metal films (Au, Cu, or Ag) and a polymer dielectric are obtained and analyzed. A new sensor is proposed, which will utilize the ferroelectric P(VDF-TrFE) copolymer separating metal films. This might be a perspective idea for the creation of tunable plasmonic sensors. The dependencies of the angular position of a surface plasmon resonance versus the thicknesses of structure’s layers, as well as versus the refractive index of the medium contacting to the free surface of a sensor, are considered. This makes it possible to carry out the approximate search for optimal constructive parameters of a sensor, namely, the thicknesses of metal and polymer layers, and to make conclusion about its resulting sensitivity and working range. It is found that the sensors based on a single metal film and a couple of such films separated by a polymer differ 1 ... 1.3 times in the sensitivity (single metal film demonstrates a more rapid resonant angle shift with analyte refractive index variation). It is established that the employment of Au, Cu, or Ag gives no significant changes in the sensitivity of a two-metal-layer sensor with a polymer, but the widest refractive index registration range may be expected for a Cu-based sensor.

Characterization of leaf surface phenotypes based on light interaction

BackgroundLeaf surface phenotypes can indicate plant health and relate to a plant’s adaptations to environmental stresses. Identifying these phenotypes using non-invasive techniques can assist in high-throughput phenotyping and can improve decision making in plant breeding. Identification of these surface phenotypes can also assist in stress identification. Incorporating surface phenotypes into leaf optical modelling can lead to improved biochemical parameter retrieval and species identification.ResultsIn this paper, leaf surface phenotypes are characterized for 349 leaf samples based on polarized light reflectance measured at Brewster’s Angle, and microscopic observation. Four main leaf surface phenotypes (glossy wax, glaucous wax, high trichome density, and glabrous) were identified for the leaf samples. The microscopic and visual observations of the phenotypes were used as ground truth for comparison with the spectral classification. In addition to surface classification, the microscope images were used to assess cell size, shape, and cell cap aspect ratios; these surface attributes were not found to correlate significantly with spectral measurements obtained in this study. Using a quadratic discriminant analysis function, a series of 10,000 classifications were run with the data randomly split between training and testing datasets, with 150 and 199 samples, respectively. The average correct classification rate was 72.9% with a worst-case classification of 60.3%.ConclusionsLeaf surface phenotypes were successfully correlated with spectral measurements that can be obtained remotely. Remote identification of these surface phenotypes will improve leaf optical modelling and biochemical parameter estimations. Phenotyping of leaf surfaces can inform plant breeding decisions and assist with plant health monitoring.

Reversible Handedness Inversion and Circularly Polarized Light Reflection Tuning in Self-Organized Helical Superstructures Using Visible-Light-Driven Macrocyclic Chiral Switches.

A series of macrocyclic azobenzene-based photoswitches have been judiciously designed, synthesized, and characterized. In the molecular structures, binaphthyl is covalently linked to ortho-positions of azobenzene, and four different substituents are linked to 6,6'-positions of binaphthyl. The photoswitches show enhanced helical twisting power (HTP) when doping in commercially available achiral liquid crystals to form self-organized helical superstructures, i.e., cholesteric liquid crystals (CLCs). All the photoswitches exhibit reversible photoisomerization driven by visible light of different wavelengths in both organic solvent and liquid crystals. The photoswitches with shorter substituents enable handedness inversion of CLCs upon photoisomerization. These are the first examples of ortho-linked azobenzene-based photoswitches that enable handedness inversion in CLCs. The photoswitches with longer substituents display only HTP values decreasing while maintaining the same handedness.

Characterizing optical phase-change materials with spectroscopic ellipsometry and polarimetry

This paper discusses the fundamentals, applications, potential and limitations of polarized light reflection techniques for the characterization of phase-change materials (PCMs). These techniques include spectroscopic ellipsometry, time-resolved ellipsometry and imaging ellipsometry as well as polarimetry. We explore the capabilities of spectroscopic ellipsometry in the determination of the extinction coefficient of PCMs and the capabilities of imaging ellipsometry to characterize PCMs. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about crystallization/amorphization kinetics and mapping anisotropies.

Spectral imaging of normal, hydrated, and desiccated porcine skin using polarized light.

.SignificanceSpectroscopic and structural imaging of tissue layers is important for investigating tissue health. However, investigating superficial tissue is difficult using optical imaging, due to the convolved absorption and backscatter of light from deeper layers.AimThis report investigates the effects of hydration and desiccation of ex vivo porcine skin on the reflectance of polarized light at different wavelengths (light-emitting diodes).ApproachWe developed a spectroscopic polarized imaging system to investigate submicron changes in tissue structures. By separating polarized from depolarized backscattered light, submicron structural changes in subsurface and deeper tissue layers can be separated and monitored.ResultsThe results demonstrate that (1) polarized light reflectance is about 2%, consistent with scattering events, on average; (2) there was little wavelength dependence to the reflectance of polarized light; (3) increased hydration leads to a modest increase in total reflectance (from 0.8 to 0.9), whereas desiccation had little effect; however, hydration did not affect polarized reflectance, but desiccation slightly lowered polarized reflectance.ConclusionsHigher scattering from the reticular dermis was likely due to swelling of collagen fiber bundles in the dermal layers, which increased fibril spacing. The epidermal skin surface showed little change due to the stratum corneum resisting desiccation and maintaining hydration.

Combining polarized light microscopy with machine learning to map crystallographic textures on cubic metals

In this work, we demonstrate the possibility of gathering crystal orientation information from cubic—optically isotropic—materials using polarized light microscopy. Our method relies on a simple and inexpensive optical technique called polarized reflectance microscopy (PRM). During PRM, we capture a sequence of micrographs of chemically etched aluminum samples under different polarization angles. We then feed the measurements into a machine learning algorithm that interprets light reflection intensity as a function of polarization angle and returns the location-specific crystallographic texture across the sample surface. We discuss the physical mechanism behind the connection between polarized light reflectance and crystal orientation in this class of optically isotropic materials, and the opportunities that such a technique would open in the field of high-throughput characterization of materials.

Numerical results for polarized light scattering in a spherical atmosphere

We report numerical results for polarized light reflection from the top of a Rayleigh scattering spherical atmosphere with height-dependent single scattering albedo over a dark surface. Michael Mishchenko considered this scenario back in the 1990’s, for a plane-parallel atmosphere of unit optical thickness (OT = 1), for which radiance errors arising from neglecting polarization reaches their highest values. To further extend Mishchenko's results, we consider a value of OT = 0.25, for which the effect of atmospheric curvature is pronounced. New results are generated using three state-of-the art radiative transfer (RT) codes. These are: the MYSTIC and MCSSA models, which simulate light scattering in a true-spherical atmosphere using Monte Carlo methods; and the discrete ordinate code VLIDORT, operating with a new multiple-scatter spherical correction designed to deliver reasonable approximations to spherical-medium scattering. In this work, we report results for both single and multiple scattering; this will help to support the validation of existing and future polarized spherical RT codes, especially those using approximative methods to deal with sphericity.

Photonic Cholesteric Liquid-Crystal Elastomers with Reprogrammable Helical Pitch and Handedness.

The unique combination of the rubber-like property and the photonic helicoidal structure of cholesteric liquid-crystal elastomers (CLCEs) results in one-handed circular polarized light reflection, the wavelength of which is dictated by the Bragg relationship. Herein, a highly stretchable mechanochromic photonic CLCE film was fabricated by cross-linking mesogenic oligomers having thiol terminal groups, which further reacted to form disulfide (-S-S-) linkages. The mechanically stretched photonic CLCE film reflected both right- and left-handed circular polarized lights with a blue-shifted color. The helicoidal pitch and handedness controlled by the applied strain were programmed through a dynamic exchange reaction between the -S-S- linkages, thus realizing the patterning at selective regions. The pattern almost vanished under unpolarized daylight but was visible under circularly polarized light when the patterned photonic CLCE film had been heated above its isotropic temperature. The hidden patterns of the heat-treated CLCE film reappeared under unpolarized daylight when stretched, demonstrating a data encryption ability. These patterned photonic elastomers can be uniquely used in sensors, actuators, soft robotics, flexible displays, data encryption, and anticounterfeiting applications with a mechanochromic camouflage response.

Laser Nanostructuring for Diffraction Grating Based Surface Plasmon-Resonance Sensors

The surface plasmon resonance properties of highly regular laser-induced periodic surface structures (HR-LIPSSs) on Si, functionalized with Au nanoparticles (NPs), were investigated. In particular, the spectral dependencies of polarized light reflectance at various angles of incidence were measured and discussed. It is found that the deposition of Au NPs on such periodically textured substrates leads to significant enhancement of the plasmon resonance properties, compared to that measured on planar ones. This effect can be used to improve the efficiency of localized-plasmon-resonance-based sensors.

Structural Domain Imaging and Direct Determination of Crystallographic Orientation in Noncentrosymmetric Ca3Ru2O7 Using Polarized Light Reflectance*Supported by the National Key Research and Development Program of China (Grant Nos. 2019YFA0308602 and 2016YFA0300500), the National Natural Science Foundation of China (Grant Nos. 11804220, 11774305 and 11974237) and Natural Science Foundation of Shanghai (Grant No. 20ZR1428900).

The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state, along with multiple other closely competing interactions. However, the structural domain formation in this material often complicates the study of intrinsic material properties. It is crucial to fully characterize the structural domains for unrevealing underlying physics. Here, we report the domain imaging on Ca3Ru2O7 crystal using the reflection of polarized light at normal incidence. The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal, and gives rise to a peculiar contrast. The domain walls are found to be the interfaces between 90° rotated twin crystals by complementary magnetization measurements. A distinct contrast in reflectance is also found in the opposite cleavage surfaces, owing to the polar mode of the RuO6 octahedra. More importantly, the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain. Such an approach provides an efficient yet feasible method for structural domain characterization, which can also find applications in noncentrosymmetric crystals in general.

The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix

Waveguide optical properties of a cholesteric liquid crystal (CLC) layer with a deformed lying helix (DLH) have been studied by numerical simulations using the finite difference time domain method. The DLH structure, when the helix’s axis is oriented in plane of a CLC layer, is induced by an electric field in a virtual CLC cell with periodic (planar/homeotropic) boundary conditions at one of the alignment surfaces. This in-plane helical structure is stable only in a permanently applied electric field providing the helix deformation. In this work the polarized light reflectance spectra have been studied at different electric fields and light impingement into a waveguide formed by the DLH layer. It is found that for light propagating along the helix axis the reflectance spectrum has multiple stop-bands centred at wavelengths , which is different from set of bands located at , and characteristic of CLC spectra for the Grandjean-plane textures subjected to distortion by an electric or magnetic field perpendicular to the helix axis, where j is a natural number, p is the helix pitch and is the average refractive index. Each of the higher order (j > 1) bands consists of three polarization-dependent sub-bands. In the case of an amplifying CLC DLH layer, depending on an extent of the helix deformation, the lasing modes can be excited at different edges of the sub-bands. While at the strongest deformation the lasing is preferable at the edges of the central sub-band; a lower extent of deformation makes favourable conditions for the lasing at edges of the two other sub-bands.

Optical characterization of tip bended Vertically Aligned Carbon Nanotubes array

Vertically Aligned Carbon Nanotube arrays (also termed as VACNTs or CNT forest) have recently found to be transformable to a reflective mirror from a naturally black absorber. The feature of improved reflectance can be attained by the controllable tip bending process using the bottom surface of a rotated cylindrical tool (the process called micro-mechanical bending (M2B)). In this paper, the polarized light reflectance of bent and compacted region of the CNT forest using M2B method has been investigated. We observed that reflectance from the processed CNT zone was highly dependent on the angle of incidence and polarization state of the incident laser. For the first time, the refractive index of the tip bent CNT forests by M2B method was investigated and found to be in a range of ∼1.8.

Variation in the circularly polarized light reflection of Lomaptera (Scarabaeidae) beetles.

An extended spectroscopic study on the left-through-left circularly polarized reflection spectra of a large number of beetles from the Australasian Scrabaeidae:Cetoniinae of the Lomaptera genus was undertaken. We have obtained a five-category spectral classification. The principal spectral features, which even within the genus range from blue to infrared, are related to structural chirality in the beetle shells. The detailed features of each spectral classification are related to different structural perturbations of the helix, including various pitch values and abrupt twist defects. These spectral characteristics and associated shell structures are confirmed on the basis of simple modelling. An important conclusion from our study is that the simple helical structure resulting in a single symmetric Bragg peak is not the dominant spectral type. Rather the reality is a rich tapestry of spectral types. One intriguing specimen is identified via a scanning electron micrograph to consist of a double interstitial helix leading to a particular double-peak spectrum.

Ellipsometry method application in optics of inhomogeneous media

Physico-mathematical methods of modeling and measurements of polarization optical characteristics of “inhomogeneous surface layer – inhomogeneous medium” reflective system have been improved based on generalization of the polarized light reflection theory in the Born approximation from inhomogeneous media interface. Theoretical and experimental justification for simultaneous application of multi-angular and scanning ellipsometry methods is given for gradient optics elements in inhomogeneous layer presence on the surface of the optical detail. The measurement of the main ellipsometric parameters – linear reduced polarization azimuth Ψand phase difference Δbetween mutually orthogonal p– and s– components of a reflected polarized light beam – was carried out on a dual-channel installation, in which the scheme of measurements of polarization parameters Ψand Δby balanced (null) ellipsometry method is used in the first channel; the photometric scheme of measurements of parameters Ψand Δby Fourier method of output detection is used in the second channel. Such separation of channels gives the possibility for measuring of polarization parameters of reflected light beam separately and, thereby, improving the accuracy of ellipsometric measurements in relation to observable physical quantity of measurements object. The values of refractive index n(r) and absorption index k(r) were calculated by axial section of selfoc on the basis of measurements of polarization parameters Ψand Δwith angle of incidence of the light beam φ=45о within the limits of scanning ellipsometry method and a model of geometrically flat interface of homogeneous media. Empirical data indicated the model incorrectness of the geometrically flat interface for polarization measurements of refractive index distributionn(r) and absorption index k(r) in gradient optical engineering elements. For the reflective system “inhomogeneous surface layer – inhomogeneous medium” the refractive index n(r) change by axial section of an element r is proportional to phase difference Δ(r) between mutually orthogonal components of a reflected light beam. At the same time the linear reduced polarization azimuth Ψ(r) in the section gradient optical element varies slightly. The main proportions for calculation of refractive index nсand thickness dсof superficial layer in each local point r of selfoc are adduced on the basis of the ellipsometry equation, obtained within the framework of the polarized light reflection Born theory. Empirical data of experimental researches make it possible to give quantitative assessment of surface processing quality for optical engineering elements. Elaborated ellipsometric techniques are recommended in technological production of optical base assemblies with gradient and fiber optics elements.

Photo-Thermal Modulation of Cholesteric Liquid Crystals with a Dual Circularly Polarized Light Reflection Band

In this study, we developed a cholesteric liquid crystal (Ch-LCs) composite with a dual (both right- and left-) circularly polarized light reflection band by utilizing a polymer template method, where a glassy Ch-LCs oligomer (GCLCO) with left-handed helical structure containing azobenzene dopant (AD) was infiltrated into the polymer template with right-handed helical structure. Photo-optical, thermal as well as glass-forming properties of the Ch-LCs film with a dual circularly polarized light reflection band were investigated, trans–cis (E–Z) photoisomerization of the AD in the GCLCO induced pitch length shortenings in response to the formation of the Z isomers by 365 nm ultraviolet (UV) irradiation, resulting that the reflection band of left-handed circularly polarized component of light in the Ch-LCs composite after UV irradiation exhibited a blue shift. What is more, the changed reflected color could be fixed in Ch glassy solid by rapid cooling from their Ch temperatures to below glass transition temperature (Tg), in which the photo and thermal isomerization of the AD could not influence the Ch pitch any longer and the color was stably stored. This technique has great applications such as tunable lasers, optical sensors, and security technology.

圆偏振光在手征负折射材料表面的反射和极化特性研究

圆偏振光在手征负折射材料表面的反射和极化特性研究

Laboratory Studies of Polarized Light Reflection From Sea Ice and Lake Ice in Visible and Near Infrared

As the knowledge of polarized reflection from ice may be important for understanding radiative transfer in ice and be of potential value in imaging applications, spectral reflectances and linear polarization of sea ice and lake ice have been measured in visible and near infrared (NIR) (350–2500 nm) at nadir and the specular direction, respectively. Results are presented for three ice types: 1) black lake ice (bubble-free ice); 2) lake ice with air bubbles; and 3) sea ice with brine pockets but no air bubbles. The effects of air bubbles and brine pockets on spectral reflectance and degree of linear polarization (DLP) are investigated in ice of 0.15 m thick at $-20 ^{\circ}\hbox{C}$ . Spectral reflectances are sensitive to ice condition, consistent with earlier studies of lake ice and sea ice. The DLP of ice in the specular reflection direction is found to be inversely but nonlinearly proportional to reflectance. The case of 1) polarized clearly more light than 2) or 3) in visible wavelength, but they were similar in NIR wavelength, implying the significant contribution of polarization derived from specular reflection. Apparent changes are predicted as volume scattering from air bubbles and brine pockets play an important role in decreasing the DLP of ice in the specular direction.

A Novel Interactive 3D Display Based on Half-Silvered Mirror

3D displays become more and more prevalent. Most 3D displays are so complicated and expensive that they are unavailable for ordinary people. Moreover, none of them are interactive. In this paper, we introduce a novel interactive low cost 3D display based on polarized light phenomenon. The system includes a touch box and two mutually perpendicular LCDs with a piece of half-silvered glass which bisects them. This novel system permits: (1) superior quality of display and (2) a novel interactive experience. The principle of the linearly polarized light reflection and refraction is deduced by Fresnel equations. The touch box is used to simulate 3D mouse, which consists of two touch panels. To show how it works, we implemented a 3D game application and a set of interactions are introduced.