Synthesis,growth and optical properties of semi organic non linear optical single crystal: l-Arginine acetate

In the recent past, nonlinear optical materials are getting attention in the field fibre optic communication and optical signal processing. In the present study, the title compound was successfully synthesized by conventional chemical reaction and then the single crystal was grown by slow evaporation solution growth technique. l-Arginine acetate (LAA) is semi organic non linear optical single crystal and crystallizes in noncentrosymmetric space group. The grown good quality single crystals have been analyzed by different characterization analyses such as powder X-ray diffraction, high resolution X-ray diffraction (HRXRD), Raman spectroscopy, photoluminescence, SEM, micro-hardness, thermal and birefringence analyses.     

Investigations of crystalline and optical perfection of SHG oriented KDP crystals

Potassium dihydrogen phosphate (KDP) crystals grown along the type-II phase-matching direction were investigated for crystalline and optical perfection. High-resolution X-ray diffraction (HRXRD) technique was used for investigating crystalline perfection. UV–VIS transmission, Mach–Zehnder interferometry, birefringence interferometry and conoscopy were performed for optical characterization. HRXRD results show that the grown crystals have good structural perfection. A uniform transmittance of 92% was observed in the visible region of the spectrum. Straight and parallel fringes were observed in Mach–Zehnder interferometric studies. A symmetrical fringe pattern was obtained in conoscopy images. These interferometric results suggest that the optical homogeneity of the grown crystal was good and not influenced by the growth technique.     

四方晶系SBN晶体中位错光双折射像的理论计算和实验观察

本文计算了铌酸锶钡(SBN)晶体中沿光轴的位错双折射像的反衬,计算中考虑了光弹系数的各向异性,结果表明与各向同性计算相比刃位错双折射像中的花瓣有伸长的趋势,螺位错无反衬,并与实验结果作了比较。     

光学平衡桥式电流互感器的设计

为了消除传感头随温度变化的线性双折射对光学电流互感器性能的影响,提出了光学平衡桥式电流互感器的概念,并给出了设计原理.推导了与温度有关的线性双折射导致的线偏振光方化角变化量的解析式,并计算了用1/2波片来消除线性双折射影响时波片光轴的方向.给出了光学平衡桥的工作原理和信号处理的方法,推导出计算电流的表达式.进行了实验研究,螺线管电流为2 A,温度在20℃-65℃范围变化时,所设计互感器的输出误差在2.96%以内.提出的光学平衡桥式电流互感器,解决了原有方法存在的线性双折射随温度变化对测量精度影响的难题,有利于促进光学电流互感器的实用化进程.     

基于各向异性晶体的光学微分运算

光学微分运算是边缘图像的光学检测核心原理,与传统的数字图像处理方法相比,具有效率高、结构简单且无需考虑算法和功耗等优点.本文提出一种基于各向异性晶体的光学微分运算装置,用定制的晶体片实现光的空间分化,从而实现多角谱分量下的全方位边缘成像.本文中的方案需要将光束的左右旋圆偏振分量横向分离,再对中间部分的线偏振光进行滤波处理.该方案主要是基于各向异性晶体的双折射效应,整个装置整合为一条笔直的光路,与自旋霍尔效应和超表面相比,具备原理简单、成本较低且成像稳定的优点,不过对晶体的厚度有较高的要求.实验结果也较为理想地验证了此方案,未来可望在量子观测、生物细胞和医学等领域实现一定潜在应用.     

Temperature effect on the diffraction efficiency of the liquid crystal spatial light modulator

Temperature effect on the diffraction efficiency of the liquid crystal spatial light modulator is investigated. The birefringence of the liquid crystal as functions of the temperature is measured with and without the power supply. It is shown that the birefringence reduces while the temperature increases. And the change magnitude of the birefringence has an exponential decay relation with the applied voltage for different temperature intervals. The scalar diffractive theory is used to analyze this effect on the diffraction efficiency. It indicates that the diffraction efficiency decreases from 98.7% to 27.2% while the temperature increases from 10 to 90 °C for 16 quantified levels. At last, temperature effect on its applications in optical testing and wavefront correction is discussed. It indicates that it has almost no effect on optical testing, but has an important effect on wavefront correction. And two solutions are given to eliminate this effect.     

Quasi-phase-matched optical activity effect in “gyroelectric” crystals and its applications

“Quasi-phase matching” is first introduced to the optical activity (OA) effect and a wave coupling theory for the quasi-phase-matched (QPM) OA effect in periodically poled “gyroelectric” crystals is developed. The OA effect is observed clearly even though the propagating direction of light deviates far from the optical axis in the QPM crystal with both optical activity and natural birefringence. The QPM OA effect provides a special way to determine the gyration coefficients that cannot be observed by the normal OA effect, and it provides a principle for building optical filters without external field.     

Diffractive Multifocal Focusing of Gaussian Beams

The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the quasi-optical approximation. It is shown that when a Gaussian beam illuminates a bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The proposed diffractive method allows the focusing of the wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensive and high-power radiation.     

Diffractive Focusing of a Gaussian Beam

The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the framework of the quasi-optical approximation. It is shown theoretically and experimentally that when a Gaussian beam illuminates such a type of bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The diffractive method proposed allows the focusing of wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensity and high-power radiation.     

Diffractive Multifocal Focusing of Gaussian Beams

The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the quasi-optical approximation. It is shown that when a Gaussian beam illuminates a bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The proposed diffractive method allows the focusing of the wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensive and high-power radiation.     

Temporal characteristics of narrow-band optical filters and their application in lidar systems

The temporal characteristics of two different narrow-band optical filters at 532 nm are reported. Both filters operate on the 4P(1/2) - 8S(1/2) atomic transition of potassium vapor, where the 4P(1/2) state is excited by a 770-nm, 10-ns laser pulse. The filters operate on the principle of circular birefringence induced by either the Faraday effect or two-photon transition, which is confirmed by experiments. The characteristic decay times of the filters are 5 and 0.015 mus, which is significant for the design of optical gating and signal processing with matched filters for ocean lidar.     

Magnetogyrotropy in twisted CdS crystals

In this paper the optical activity (gyrotropy) induced by a simultaneous action of a magnetic field and a torsion in hexagonal CdS crystals has been investigated. The crystal having undergone to both external influences is placed between two crossed polarizers. The spectral course of transmittance of this system near the isotropic point of CdS (the wavelength where the birefringence changes its sign) is studied in the experiment. An explanation of the experimental results is given by using the model of elliptical birefringence in anisotropic gyrotropic crystals. Taking into account the superposition of both external influences, it has been proved that the torsion generates gyrotropy whose parameter changes its sign in the isotropic point.     

Artificial ultrasound anisotropy of crystals in the range of X-ray frequencies

Phenomenon of artificial ultrasound anisotropy is revealed in crystals in the range of X-ray frequencies and an attempt is made to explain this effect theoretically for the case of the Bragg-Laue diffraction. It is established that an isotropic crystal becomes, under action of ultrasound, optically anisotropic like a uniaxial crystal with the optical axis along the direction of the external action; this axis is the symmetry axis and causes birefringence.     

Image aberrations in an acousto-optical tunable filter

The problem of deformation of images due to diffraction from 3D diffraction gratings (in particular, the grating formed by an acoustic wave in an acousto-optical filter) is considered. For the first time, the exact solution is obtained without using the small birefringence approximation. The form of aberrations induced by main types of acousto-optical filters is analyzed and illustrated by calculations.     

Determination of crystalline perfection,optical indicatrix,birefringence and refractive-index homogeneity of ZTS crystals

Single crystals of the semi-organic non-linear optical material zinc tris (thiourea) sulphate (ZTS) were grown by slow evaporation solution growth technique. The crystals were characterized for crystalline perfection and optical homogeneity using high-resolution X-ray diffraction (HRXRD) and optical interferometric techniques. The FWHM of 6 arc sec in HRXRD rocking curve shows the good crystalline quality. Transmittance of ∼75% shows that the crystal is free from volume defects. Conoscopy was used to assess the optical quality and investigate the optical indicatrix of the grown crystal. Birefringence values of the crystal along the three principal crystallographic axes were measured using birefringence interferometry. Mach–Zehnder interferograms exhibit good refractive-index homogeneity of the grown crystal.     

Acousto-optic processing of images in visible and ultraviolet light

The paper concerns processing of optical images by means of tunable acousto-optic filters. Experimental and theoretical research showed that longitudinal chromatic aberrations cause a suffcient decay of the spatial resolution in the devices. It is shown that a proper choice of an optical cheme of an imager reduces the longitudinal aberrations all over the tuning range of the filters.     

Phase-resolved functional optical coherence tomography: simultaneous imaging of in situ tissue structure, blood flow velocity, standard deviation, birefringence, and Stokes vectors in human skin

We describe a phase-resolved functional optical coherence tomography system that can simultaneously yieldin situ images of tissue structure, blood flow velocity, standard deviation, birefringence, and the Stokes vectors in human skin. Multifunctional images were obtained by processing of analytical interference fringe signals derived from two perpendicular polarization-detection channels. The blood flow velocity and standard deviation images were obtained by comparison of the phases from pairs of analytical signals in neighboring A-lines in the same polarization state. The analytical signals from two polarization-diversity detection channels were used to determine the four Stokes vectors for four reference polarization states. From the four Stokes vectors, the birefringence image, which is not sensitive to the orientation of the optical axis in the sample, was obtained. Multifunctional in situ images of a port wine stain birthmark in human skin are presented.     

Properties of cis-and trans-polyisoprene blends

Measurements of thermodynamic compatibility, technological properties, stress-strain isotherms at high elongation, birefringence, and wide-angle x-ray diffraction have been made on blends of guayule rubber (cis-1,4-polyisoprene) and trans-polyisoprene (t-PI). Both cross-linked and un-cross-linked systems, prepared by mechanical mixing and solution mixing, have been used. Blends of cis-and trans-polyisoprene show complete thermodynamic compatibility above the mp of t-PI. The technological properties measured at room temperature deteriorate with the incorporation of 20% of trans-polyisoprene. Tensile strength of blend vulcanizate measured at temperature above the melting point of t-PI crystals is increased and the values of compression set are comparable. The critical value of λ at which the upturn occurs in the Mooney-Rivlin plot decreases with increase in t-PI. Studies on WAXD and birefringence show that t-PI does not act as a nucleating site for crystallization of cis-PI. Intensity of a new ring at 6.61 Å, which appears on stretching the elastomer, decreases qualitatively with the addition of t-PI. The stress optical coefficient (SOC) measured at room temperature decreases with higher amounts of t-PI, indicating no cocrystallizability on stretching. The SOC, however, increases when the measurement is made above the melting point of the crystals.     

Diffraction of IR radiation by ultrasound in tellurium single crystals

The optic, acoustic, and acousto-optic properties of tellurium single crystals are considered to analyze the possibilities of applying this material in acousto-optic filters to control mid- and far-IR radiation. The results of measuring the optic and acousto-optic parameters of a tellurium crystal are reported. The isotropic and anisotropic light diffraction by ultrasound in the crystal is investigated. The wide-aperture geometry of interaction in tellurium is implemented and an acousto-optic figure of merit M ₂ of a tellurium crystal exceeding 10 × 10^?15 s³ g^?1 is experimentally obtained.     

Creation of Multiple Subwavelength Focal Spot Segments Using Phase Modulated Radially Polarized Multi Gaussian Beam

Based on the vector diffraction theory,the effect of complex phase filters on intensity distribution of a radially polarized multi Gaussian beam in the focal region of high NA lens is theoretically investigated.It is observed that a properly designed multi belt complex phase filter can generate subwavelength novel focal patterns including splitting of focal spots and generation of multiple focal spot segments such as eight,six and four focal spots along the optical axis are obtained.We expect that such an investigation is useful for optical manipulation and material processing,multiple high refractive index particle trapping technologies.