129I and125Te Mössbauer studies of polyvinyl alcohol films doped with iodine

¹²⁹I and¹²⁵Te Mössbauer measurements have been performed on unidirectionally stretched iodine-doped polyvinyl alcohol (PVA) films which are widely used as optical polarizers. From the¹²⁹I measurements iodine is observed to be in the form of linear polyiodides, I ₃ ^– and I ₅ ^– , lying parallel to the stretch direction of the PVA films. From the¹²⁵I emission Mössbauer measurements the structural arrangement of the iodine-PVA complex is also discussed.     

A compact optical isolator using a Y3Fe5O12 crystal for near infra-red radiation

Using a Y₃Fe₅O₁₂ crystal as a Faraday rotator material, a samarium cobalt permanent magnet and two iron yokes, a compact optical isolator was constructed at 1.153m for optical transmission systems. The developed isolator is 13 mm in diameter and 25 mm in length, including two polarizers. The isolator characteristics are 1.3 dB forward loss and greater than 30 dB backward loss. A broadband isolator is realized by inserting a 45 degree Faraday rotator and an optically active 45 degree quartz rotator between the two polarizers set at 90 degrees in relation to each other.     

Attenuation characteristics of a light attenuator combined by polarizers with different extinction ratios

This paper deals with a systematical analysis and an algorithm of attenuation characteristics of a light attenuator combined by n pieces of polarizers (n-LACP) whose extinction ratios are different from each other.The attenuation ratio expression of a two-LACP is deduced.We find that the monotonic attenuation interval depends on the first polarizer and that the attenuation range depends on the second one.For the three-LACP,a method for obtaining a monotonic attenuation interval is proposed.Moreover,the attenuation ratio expression is demonstrated.Analysis and experiment show that when the initial status of the three-LACP is at the maximum output,if the second or third polarizer rotates alone,the minimum attenuation ratios can reach K-1 2 and K-1 3,respectively,and if the first polarizer rotates,a minimum attenuation ratio of K-1 2 K-1 3 can be obtained (K 1,K 2 and K 3 represent the extinction ratios of the three polarizers in turn).Furthermore,the attenuation ratio expression of n-LACP and the relevant attenuation characteristics are proposed.The minimum attenuation ratio of an n-LACP is (K 2 K 3 ··· K n)-1.     

Light polarization in iodine-doped polyvinyl alcohol films

¹²⁹I Mössbauer measurements have been performed on unidirectionally stretched iodinedoped polyvinyl alcohol(PVA) films which are widely used as optical polarizers. In the films iodine is observed to be in the form of I^?, I ₃ ^? , and I ₅ ^? and the stretch of the films increases the abundance of the polyiodides, I ₃ ^? and I ₅ ^? . In the stretched PVA films, it has become clear that the linear polyiodides lie parallel to the stretching direction.     

Optimization of the structure of an optical fiber polarizer with a metal film at a wavelength of 980 nm

The dependence of the extinction ratio of a 980-nm fiber polarizer with an Al film on the thickness of magnesium fluoride buffer layer has been experimentally and theoretically investigated. At the optimal thickness of the buffer layer, h _b = 0.078 (normalized to the wavelength), extinction ratios of 23 and 41 dB were obtained for polarizers having fiber shell residual layers of 2.01 and 1.607 μm, respectively. The optimal thin-film structure is determined, which will make it possible to design polarizers with extinction ratios up to 100 dB.     

Magnetorefractive effect in manganites with a colossal magnetoresistance in the visible spectral region

The magnetotransmission, magnetoreflection, and magnetoresistance of the La_0.7Ca_0.3MnO₃ and La_0.9Ag_0.1MnO₃ epitaxial films have been investigated. It has been found that the films exhibit a significant magnetorefractive effect in the case of reflection and transmission of light in the fundamental absorption region both in the vicinity of the Curie temperature and at low temperatures. It has been shown that the magnetorefractive effect in the infrared spectral region of the manganites is determined by a high-frequency response to magnetoresistance, whereas the magnetorefractive effect in the visible spectral region of these materials is associated with a change in the electronic structure in response to a magnetic field, which, in turn, leads to a change in the electron density of states, the probability of interband optical transitions, and the shift of light absorption bands. The obtained values of the magnetotransmittance and magnetoreflectance in the visible spectral region are less than those observed in the infrared region of the spectrum, but they are several times greater than the linear magneto-optical effects. As a result, the magnetorefractive effect, which is a nongyrotropic phenomenon, makes it possible to avoid the use of light analyzers and polarizers in optical circuits.     

System for measuring optical admittance of a thin film stack

A new method based on the polarization interferometer structure has been applied to measure the optical admittance, the refractive index and thickness of a thin film. The structure is a vibration insensitive optical system. There is one Twyman-Green interferometer part to induce a phase difference and one Fizeau interferometer part to induce the interference in the system. The intensities coming from four different polarizers were measured at the same time to prevent mechanical vibration influence. Using the polarization interferometer, the optical admittance, the refractive index and thickness of a single layer of Ta₂O₅ thin film has been measured. The measurement results were compared with the results obtained by ellipsometer. The results meet reasonable values in both refractive index and thickness.     

A simple Fourier photopolarimeter with rotating polarizer and analyzer for measuring Jones and Mueller matrices

The classic and simplest polarimetric scheme of examining a “sample” by placing it between a pair of linear polarizers and observing the intensity of the transmitted light can be transformed into a powerful photopolarimeter if the two polarizers are synchronously rotated at different speeds and the transmitted flux is linearly detected and its periodic waveform Fourier analyzed. In particular, if the angular speed of rotation of one polarizer is ω and that of the other is 3ω, the detected signal has the waveform, i=a₀ + Σ⁴_n=1a_n cos nω_ft + b_n sin nω_ft, where ω_f=2ω is the fundamental frequency. The nine Fourier amplitudes a₀ and (a_n, b_n), n=1,2,3,4, to be derived by performing a discrete Fourier transform (DFT) of the signal i, determine all nine elements of the 3×3 submatrix M_3×3 obtained by deleting the fourth row and fourth column of the Mueller matrix M. If the sample is nondepolarizing, the absolute values of all the four elements of the equivalent Jones matrix $\text{J}\text{=(J}{}_{\mathrm{ij}}\text{)}$, i,j=1,2 and their angle differences θ_ij?θ₂₂ (where θ_ij=argJ_ij) can be determined.     

基于多层膜偏振元件的软X射线磁光Faraday偏转测量

在北京同步辐射装置(BSRF)的3W1B软X射线光束线上利用自行研制的同步辐射软X射线综合偏振测量装置对Ni的M_2,3边附近(60—70 eV)进行了软X射线磁光(magneto-optical)法拉第效应(Faraday effect)的偏转测量,实验装置主要由起偏器,检偏器,样品架,圆形钕铁硼永磁铁和MCP探测器组成,偏振元件(起偏元件和检偏元件)均采用反射式非周期性Mo/Si宽带多层膜.实验采用反射起偏和反射检偏的模式,得到一系列能量范围在60—70 eV间的法拉第偏转角结果, 关键词： 软X射线 磁光Faraday效应 综合偏振测量装置 宽带多层膜     

The scattering suppression of X-rays with energy of 20–200 keV in spectrometers with Barkla polarizers

The method is proposed for estimating the polarization parameters and the scattering suppression coefficients in energy dispersive X-ray spectrometers with Barkla polarizers (EDPXRS) for X-ray fluorescence (XRF) analysis. The scatter suppression coefficients are estimated accounting primary beam polarization, secondary beams yields, detectors response function, and partial factors. Estimations of scatter suppression coefficients due to polarization do not require the use of Stokes parameters and matrices. The method gives the possibility to make polarization-related corrections in calculations by XRF theory based on scattering cross sections of unpolarized beams. Calculations clarify early estimations of EDPXRS parameters with Barkla polarizers in the 20–200 keV range. The polarizing ability at δ = 7° deviations varies from 0.973 at 20 keV to 0.863 at 200 keV. The analyzing ability of registration system is about the same. In a simple XRF version on a synchrotron radiation with Barkla polarizer, the scattering can be decreased 60 times at 20 keV and 11 times at 80 keV with δ_s = 3°. In EDPXRS, the scatter suppression factor varies within 10–4.2 at deviations δ = 10° and within 20–4.8 at δ = 7°. The scatter suppression at low energies is determined by angular factor and background and at high energies is limited by energetic factors.     

Determination of optical birefringence of S-benzylisothiouronium chloride and S-benzylisothiouronium nitrate using Cauchy’s two term model by the channelled spectrum method

The channelled spectrum method was used for measuring the birefringence of anisotropic organic single crystals S-benzylisothiouronium chloride (SBTC) and S-benzylisothiouronium nitrate (SBTN). Crystals of uniform thickness were placed between crossed polarizers and illuminated with a tungsten source. The resulting pattern was analyzed to deduce the birefringence and its dispersion across the visible spectrum. Cauchy’s two term formula was applied to fit the experimental data. The Cauchy’s coefficients A and B were obtained by solving the linear equations using MATLAB^®. The wavelength dispersion of birefringence was calculated.     

Compensated Polarization Scrambler for Raman Depolarization and Intensity Measurements on Microsamples

It has long been recognized ^1,2,3,4,5 in measuring relative intensities and depolarization ratios of Raman lines that prism and grating spectrometers have different transmittances for light polarized parallel (T_∥) and perpendicular (T_⊥) to the slit. Several methods have been used to give equal instrument response to parallel and perpendicular polarization. Stitt and Yost³ used a Nicol prism parallel to the high-transmittance direction of the spectrometer, combined with a rotatable mica half-wave plate to transmit either vector to the Nicol prism. This method has the advantage of having a higher spectrometer transmittance, but the mica plate gives exact half-wave retardation at only a single wavelength. A mica quarter-wave plate ^4,5 averages the transmittances of the spectrometer for the two polarization directions, but is also wavelength dependent. Virtually achromatic circular polarizers have been designed and constructed ^6,7, but these devices are too bulky and expensive for the clear apertures needed for fast spectrometers.     

Application of weigert effect to the pseudocoloration of a black and white signal

We propose here a method to transform the grey levels of a black and white transparency into different colours. The transparency to be processed, illuminated by a beam of linearly polarized white light, is twice recorded on a photograph silver-chloride emulsion. The direction of the light vector is rotated through π/2 between the exposures. The resulting plate is characterized by a spatially varying anisotropy. The main point is that the wavelength λ_B and λ_D, respectively corresponding to the cancellation of birefringence and dichroism, are function of the irradiance of the signal and of the successive exposure times. The plate is then illuminated in white light and observed between two polarizers P and A. It reconstructs an achromatic image of T when the respective axes of P and A are mutually perpendicular. A rotation of A from its setting crossed with P generate a colour distribution on the plate.     

Subwavelength gratings fabricated on semiconductor substrates via E-beam lithography and lift-off method

We present results of the fabrication and measurements on reflective polarizers consisting of stacked bi-layer subwavelength metal gratings prepared on GaAs (100) substrates. These linear gratings were fabricated using electron-beam direct-writing lithography and the lift-off method with periods less than the wavelength of light used for measurements. At normal incidence, the polarizer reflects the light polarized perpendicular to the grating lines (transverse magnetic polarization, TM polarized) but absorbs parallel-polarized light (transverse electric polarization, TE polarized). By optimizing structural parameters, the polarization extinction ratio close to 20 has been experimentally achieved at wavelength of 650 nm.     

New fast and memory-sparing method for rigorous electromagnetic analysis of 2D periodic dielectric structures

A method is presented that performs the exact electromagnetic analysis of 2D periodic dielectric structures of arbitrary profile or index distribution and possibly large period. The generalized source method is used to formulate the problem of light diffraction in the form of a volume integral equation reduced to a linear equation system, which is solvable by known fast algorithms. The calculation time and required memory are linearly proportional to the total number N_o of considered diffraction orders instead of N_o³ typical for conventional methods. Numerical examples are provided to demonstrate the potential of the method for the analysis of complex periodic structures.     

Brewster’s angle polarizer design based on a gyrotropic double-periodic perforated layer

This paper is devoted to the study of the features of artificial gyrotropic magneto-dielectric layer with two-dimensional periodicity. Such a layer can be used in the development of the polarizers operating in the microwave and optical ranges. Analytical solution of a plane wave scattering from a double-periodic gyrotropic layer is obtained by the Method of Integral Functionals in the quasi-static approximation. The numerical results allow to realize the TE- and TM-pass Brewster’s angle polarizers.     

A Hermite WENO reconstruction-based discontinuous Galerkin method for the Euler equations on tetrahedral grids

A Hermite WENO reconstruction-based discontinuous Galerkin method RDG(P₁P₂), designed not only to enhance the accuracy of discontinuous Galerkin method but also to ensure linear stability of the RDG method, is presented for solving the compressible Euler equations on tetrahedral grids. In this RDG(P₁P₂) method, a quadratic polynomial solution (P₂) is first reconstructed using a least-squares method from the underlying linear polynomial (P₁) discontinuous Galerkin solution. By taking advantage of handily available and yet invaluable information, namely the derivatives in the DG formulation, the stencils used in the reconstruction involve only von Neumann neighborhood (adjacent face-neighboring cells) and thus are compact and consistent with the underlying DG method. The final quadratic polynomial solution is then obtained using a WENO reconstruction, which is necessary to ensure linear stability of the RDG method. The developed RDG method is used to compute a variety of flow problems on tetrahedral meshes to demonstrate its accuracy, efficiency, robustness, and versatility. The numerical experiments demonstrate that the developed RDG(P₁P₂) method is able to maintain the linear stability, achieve the designed third-order of accuracy: one order accuracy higher than the underlying DG method without significant increase in computing costs and storage requirements.     

Study of the In2O3 molecule in the free state and in the crystal

ABSTRACT

The nanomaterials based on the In₂O₃ molecule are widely used as catalysts and sensors among other applications. In the present study, we discuss the possibility of using nanoclusters of In₂O₃ as molecular photomotors. A comparative analysis of the electronic structure of the In₂O₃ molecule in the free state and in the crystal is performed. For the free In₂O₃ molecule the geometry of its lowest structures, V-shape and linear, was optimised at the CCSD(T) level, which is the most precise computational method applied up to date to study In₂O₃. Using experimental crystallographic data, we determined the geometry of In₂O₃ in the crystal. It has a zigzag, not symmetric structure and possesses a dipole moment with magnitude slightly smaller than that of the V-structure of the free molecule (the linear structure due to its symmetry has no dipole moment). According to the Natural Atomic population analysis, the chemical structure of the linear In₂O₃ can be represented as O = In?O?In = O; the V-shaped molecule has the similar double- and single-bond structure. The construction of nanoclusters from ?bricks? of In₂O₃ with geometry extracted from crystal (or nanoclusters extracted directly from crystal) and their use as photo-driven molecular motors are discussed.     

Relative orientation accuracy analysis of the polarizers in a polarization CCD camera

In order to study the relative orientation accuracy of the instrument polarizers in the polarization CCD camera, a fitted function of the instrument signal, cosinusoidally modulated all along the rotation of the test polarizer, is presented. The results of numerical computation show that the relative orientation of the three polarizers in the same spectral band can be within an accuracy of ±10′ when a specific instrument output signal function is given for the condition that the random noise signal is in the ranges 0-10 (with S/N≈20).     

A TERAHERTZ PHASE FREQUENCY CHANGER WITH THE CRYSTAL QUARTZ PHASE SECTIONS

A phase frequency changer (PFC) for quasi-optical transmission line with phase sections made of crystal quartz and polarizers executed on the basis of small-period wire gratings has been considered. The PFC is intended for operation in terahertz (THz) frequency region. It has been examined at the frequency f _o= 0.89THz. The influence of the differential phase shift deviation in the sections on the output signal spectrum and the influence of the sections mismatch on the reflection signal spectrum have been considered. In the frequency region ± 10% f _o the levels of the spurious spectral components of output signal are less than −40 dB with regard to the level of the useful signal of the shifted frequency. The levels of all spectral components of the reflection signal are less than −60 dB with regard to the level of the useful component of the PFC output signal.