Bichromatic frequency conversion in potassium niobate

Two frequency components of an IR laser beam near 980 nm are simultaneously coupled into two adjacent longitudinal modes of a passive ring resonator. A potassium niobate crystal inside the resonator converts the circulating IR light into coherent blue radiation. The total conversion efficiency is enhanced by a factor of 1.4 compared with that of conventional single-mode intracavity second-harmonic generation with the same circulating total power, and we obtain a total output power of 560 mW from 780-mW IR light incident upon the cavity. The spectra of the generated blue radiation and the circulating IR light contain a number of equidistant frequency components that are due to consecutive sum- and difference-frequency mixing.     

Three-wave interference with participation of polaritons

Second-order interference with respect to the field strength during spontaneous parametric light scattering was studied under the conditions of absorption at the frequencies of idler (polariton) modes. An expression is derived that describes the scattered light intensity as a function of the scattering angle for an arbitrary shape of the nonlinear interaction region. The interference was experimentally studied for the light scattering on polaritons in a nonlinear crystal (lithium iodate, iodic acid), with a double slit placed into a pumping beam in front of the crystal.     

Bidirectional vectorial light amplification in cubic crystals with unshifted photorefractive gratings

We present a new method of light amplification based on vectorial two-wave mixing in cubic crystal via an unshifted photorefractive grating. The energy transfer between interacting waves is achieved in an experimental configuration that provides the amplitudes of modulation of refractive indices of opposite signs, Dn(1)=-Dn(2), for two orthogonal polarization modes of the interacting waves. The configuration demonstrates bidirectional amplification; i.e., the weak wave is always amplified, independent of its direction with respect to the strong pump beam. We present the results of numerical analysis along with the experimental results for a Bi(12)TiO(20) crystal with a dc applied electric field.     

α-LiIO3单晶中离子输运引起的高强度准弹性光散射

激光束通过加c向直流电压的α-LiIO₃单晶时,发生三种准弹性散射:散射光电位移矢量有特定取向且与入射光电位移矢量方向不一致者,散射光电位移矢量与入射光电位移矢量方向相同而散射带垂直c轴者以及散射光电位移矢量与入射光电位移矢量方向相同而散射带对c轴倾斜者,本文详细研究了这三种散射的空间频谱、精细结构、结构敏感性、弛豫规律以及光散射和晶体内电流密度与局部电场的关系,发现光散射发生于晶体内电流密度较大的区域,本文对三种散射的起因给予了说明:离子导体在直流电压作用下空间电荷的分布和运动引起 关键词：     

Infrared vibrational spectra of l-histidinium dihydrogen orthophosphate orthophosphoric acid (LHP)

The entire vibrational spectrum of a single crystal of l-histidinium dihydrogen orthophosphate orthophosphoric acid (LHP) was studied by infrared (IR) spectroscopy from 10 up to 4000 cm⁻¹. The polarized infrared (IR) reflectivity spectra were measured between 7 and 250 K, in the frequency range 10–600 cm⁻¹. From the IR spectral analysis, the phonon modes were classified within their symmetry species, and their longitudinal (LO) and transversal (TO) optical frequencies were calculated. A tentative assignment of the various internal modes observed in the transmissivity spectrum of LHP, between 300 and 4000 cm⁻¹, is proposed. The present study did not reveal any low-temperature structural phase transition.     

Formation and Transformation of Non‐Bessel Multiring Light Beams

A method for forming multiring light beams (MRLB) on the basis of a biaxial crystal has been developed. The intensity distribution in output MRLBs depending on the parameters of the input light beam has been calculated. For the first time an optical scheme with three axicons for highefficiency transformation of the initial laser beam to a collimated light beam with wavefront dislocation is proposed. The method permits obtaining powerful laser MRLBs which can be used in data transfer and processing systems, in nanotechnologies for manipulating particles, for technological treatment of materials, for acting on organic cells and their components, and for investigating inhomogeneities of transparent media.     

光折变晶体LiNbO_3:Fe中的特殊散射现象

用柱面透镜把经针孔滤波器扩束的激光束沿某一个方向聚焦成细丝状(或长条状),细丝状光束垂直入射到LiNbO_3:Fe晶体上,在远场位置观察散射光.我们发现光散射的方向与晶体的c轴方向不一致,不仅沿着晶体的c轴方向有散射光出现,沿光束的条形方向也出现很强的散射光.     

高功率固体激光器增益非均匀分布引起的效能亏损效应研究

激光晶体由于吸收了一部分泵浦光能量，产生的热量引起晶体内温度不均匀分布，使晶体内的折射率产生不均匀分布，对振荡光产生相应的相位调制，引起振荡光光场再分布，进而导致振荡光模式发生变化。谐振腔具有滤波作用，谐振腔会过滤掉振荡光中与谐振腔不匹配的模式，引起损耗，用MATLAB模拟晶体内温度场分布，通过计算谐振腔内基模的热致损耗及低阶模转换到高阶模的比例，并研究谐振腔中各阶模式的转换问题，为抑制高阶模并减小损耗提供理论依据。     

Spin Hall effect of light in one-dimensional photonic crystal

We established a general propagating model to investigate the spin Hall effect of light in one-dimensional photonic crystal. A polarized (spin dependent) Gaussian beam which was incident obliquely through one-dimensional photonic crystal was demonstrated. Having decomposed a polarized Gaussian beam into different plane wave components charactering individual wave vectors, we revealed the transmission coefficient and reflection coefficient of each plane wave which propagates through the one-dimensional photonic crystal. It enabled us to obtain exact solution to the electric field of transmitted and reflected beams, and the analytical formula of light intensity, accordingly. A method based upon the partial differentials with the intensity distribution of the transmitted and reflected Gaussian beams was presented to determine the transverse and longitude shifts explicitly. Spin dependent shifts in one-dimensional photonic crystal provide alternative evidence for the spin Hall effect of light.     

Ultracompact high-efficiency polarizing beam splitter with a hybrid photonic crystal and conventional waveguide structure

We propose an ultracompact high-efficiency polarizing beam splitter that operates over a wide wavelength range and is based on a hybrid photonic crystal and a conventional waveguide structure. Within a small area (15 microm x 10 microm), this polarizing beam splitter separates TM- and TE-polarized modes into orthogonal output waveguides. Results of simulations with the two-dimensional finite-difference time-domain method show that 99.3% of TM-polarized light is deflected by the photonic crystal structure (with a 28.0-dB extinction ratio), whereas 99.0% of TE-polarized light propagates through the structure (with a 32.2-dB extinction ratio). Wave vector diagrams are employed to explain the operation of a polarizing beam splitter. Tolerance analysis reveals a large tolerance to fabrication errors.     

Infrared vibrational spectra of -histidinium dihydrogen orthophosphate orthophosphoric acid (LHP)

The entire vibrational spectrum of a single crystal of -histidinium dihydrogen orthophosphate orthophosphoric acid (LHP) was studied by infrared (IR) spectroscopy from 10 up to 4000 cm⁻¹. The polarized infrared (IR) reflectivity spectra were measured between 7 and 250 K, in the frequency range 10–600 cm⁻¹. From the IR spectral analysis, the phonon modes were classified within their symmetry species, and their longitudinal (LO) and transversal (TO) optical frequencies were calculated. A tentative assignment of the various internal modes observed in the transmissivity spectrum of LHP, between 300 and 4000 cm⁻¹, is proposed. The present study did not reveal any low-temperature structural phase transition.     

表层厚度渐变一维耦合腔光子晶体的反射相位特性及其应用

利用传输矩阵法研究了表层厚度渐变的一维非对称耦合腔光子晶体的反射相位特性. 研究表明, 光子禁带内(包括缺陷模附近)的反射率在98%以上, 且基本不受表层厚度影响, 特别是, 在非正入射情况下, 简并的缺陷模随着表层厚度的变化会发生分裂; 进一步研究发现, 在缺陷模分裂处附近, TE, TM偏振的反射相位以及它们之间的相位差均敏感地依赖于表层厚度的变化, 从而使得反射光的偏振态也随表层厚度的变化而敏感变化, 其物理机理在于缺陷模分裂所造成的剧烈相位变化. 基于上述特性, 设计了一种表层厚度呈二维周期变化的一维光子晶体结构, 从该结构反射的激光经透镜聚焦后, 在聚焦区域同时存在各种偏振态(包括沿不同方向的线偏振、左旋或右旋圆偏振、椭圆偏振等)的子光束, 它们叠加后在聚焦区域将产生具有无规相位和无规偏振态的光场. 以上结果能有效降低激光的相干性, 在激光核聚变等领域有潜在的应用价值.     

Coupled mode analysis of light modulation in dielectric waveguides

A detailed analysis of electrooptic light modulation in optical waveguides is presented. Several important problems of a waveguide modulator, such as the difference of waveguide axes from crystalline electrooptic ones, the distribution of transverse and longitudinal field components of light modes, and the traveling-wave property of the modulating field, are discussed. The analysis is based on the coupled mode theory, regarding the modulation as the coupling among sidebands of unperturbed waveguide modes. The coupled mode equation is derived for the modulation in optical waveguides. It can be solved if the normal modes of the waveguide are given. Actually the equation is solved for the modulation in dielectric slab waveguides and the mechanism of modulation is discussed. The results of the analysis are applied to designing two types of waveguide modulators. In an example (10.6 μm modulator with a GaAs slab waveguide) a new efficient crystal orientation is found. The calculated phase retardation with this orientation is 0.13 rad/(V·cm) with a 1 μm thick slab. Another example of a 0.633 μm modulator using a LiTaO₃ crystal as a substrate is also described.     

Modeling light propagation in liquid crystal devices with a 3-D full-vector finite-element beam propagation method

A full-vector finite-element beam propagation method in 3-D is introduced for the simulation of light propagation in liquid crystal (LC) devices. The three electric field components are expressed in terms of mixed finite elements, providing the correct enforcement of boundary conditions. Moreover, the optical dielectric tensor of the medium can have all its nine elements nonzero, thus allowing the LC director to have an arbitrary orientation. A photonic crystal fiber with a LC infiltrated core and a homeotropic to multi-domain cell are analyzed. Comparison with other existing simulation techniques is provided, in order to validate the accuracy of the proposed method.     

Diode-pumped efficient slab laser with two Nd:YLF crystals and second-harmonic generation by slab LBO

We demonstrate a diode-pumped electro-optical Q-switched slab laser with a high optical efficiency, high pulse energy, and short pulse width with two Nd:YLF crystals inside one resonator. The single compact slab resonator can generate a 1D top-hat beam at both the far field and the near field. With a slab-geometry-design lithium triborate (LBO) crystal, efficient critical phase-matching second-harmonic generation for a 1D top-hat beam with multiple transverse modes is achieved.     

液晶稳态和瞬态多波混频与非线性光学特性

在掺杂（～3%重量比）碳纳米管和光敏取向基团的向列态液晶薄膜（5μm厚）中，在使用Ar⁺(514.5nm)为激发光做前向多波混频实验时，观察到7级的自衍射和探测光He-N e(632.8nm )的多级衍射均呈多环状结构.高斯光束中心处的光致非线性折射率系数δn～0.8. Ar⁺ (514.5nm)连续光形成光栅的时间和弛豫时间都与写入光的偏振态强烈相关.在使用Nd :YAG（532 nm）为激发光时，光栅的弛豫时间～200ms量级，且探测光He-Ne(632.8nm)的o光和e光所探 测到的动力学响应曲线是不同的. 关键词： 瞬态 稳态 多波混频 液晶     

生物医学领域中超连续激光光谱技术的研究进展

超连续谱激光指的是当泵浦激光穿过特殊光波导时,一系列的非线性效应引起入射激光束的光谱展宽,从而输出宽光谱激光束。随着超快激光和光子晶体光纤技术的发展,利用超短脉冲在光子晶体光纤中的传播链产生相干的且亮度高的超连续谱激光成为了一种理想的白光源。自从超连续谱激光源投入应用以来,其应用领域越来越广。尤其在生物医学的细胞、血液等样品分析当中,荧光光谱学、流式细胞仪、共焦显微、光学相干层析等技术都是强有力的分析工具,在采用这些先进技术的科学仪器中,超连续谱激光源成为了一种主要光学部件。首先对超连续谱激光源的国际研究进展作了详细介绍,然后对超连续激光光谱技术在显微成像、流式细胞仪、荧光寿命成像显微、荧光共振能量转移、光学相干层析、共焦显微生物医学分析等生物医学领域中的发展及应用作了综合阐述。对超连续激光光谱技术在非接触式血液制品鉴别的需求、方案及研究进展进行了重点论述,包括覆盖400～2 000 nm光谱范围的光纤化轻型超连续谱激光光源研究;采用超连续谱激光光谱方法探索不同物种血液的种属特征;根据大数据的血液样品光谱特征元数据库分析建立数学模型,利用数学模型实现对血液样品种属光谱学判定;血液鉴别光谱分析便携式整机系统研发等。对超连续激光光谱技术在生物医学领域的应用前景作了展望。     

Light-induced scattering in SBN：Cr crystal under external electric fields and its suppression

In this paper, the enhancement of light-induced scattering in congruent SBN:Cr (Sr_{0.61}Ba_{0.39}Nb_2O_6:Cr) crystals in the presence of an externally applied electric field and its suppression are studied. If a coherent image is focalized in SBN:Cr crystal without applying external electric field, the output image will remain clear, because of the weak photorefractive effect in the crystal. When a field is applied properly along the crystal axis, markedly enhanced scattering from the signal beam and the output image dispersion can be observed due to the increase of the photorefractive two-beam coupling gain and the light-induced index change in SBN:Cr crystals. By introducing a coherent or incoherent beam with higher intensity the light-induced scattering can be suppressed through the erasure of scattering gratings. The difference between coherent and incoherent beam is that the former can also amplify the signal beam as the scattered light is removed, whereas the latter can only make the signal beam revert to its initial state. The results obtained under different experimental conditions are consistent with theoretical analysis.     

Analytical model of light beam diffraction by one-dimensional electrically controlled non-uniform transmission photon PDLC structures

A mathematical model describing two-dimensional diffraction of quasi-monochromatic light beams by onedimensional electrically controlled non-uniform holographic photon structures in photopolymer dispersed liquid crystal (PDLC) materials is presented. The model describes light field distributions in the near and far field zones with allowance for the refractive index profile in the structure, light beam divergence, and encapsulation of liquid crystal molecules.     

Measuring the polarization of coherent light beams

We consider the conditions of interference of totally polarized light beams of arbitrary polarization that allow one to measure their vector characteristics by means of optical heterodyning. It is shown that the intensity of a light beam resulted from the superposition of two plane totally polarized waves with arbitrary polarizations represents a sum of two interference patterns, each of them being the result of superposition of conamed components of an orthogonal expansion of the electric field of the total light wave. The possibility of electronic registration of information in real time is demonstrated.