用于相位突变界面的广义的反射定律和折射定律

考虑到位于两物质界面上的Metasurface对光线传播行为的影响, 从费马原理和边界条件连续两种角度出发, 推导了可用于相位突变界面的广义反射与折射定律. 该定律在界面对光波的相位改变量为零的情况下, 回归为通常的反射定律和折射定律. 利用广义的折射定律和反射定律讨论了介质折射率、界面上的相位梯度等因素对光传播行为的影响, 发现利用广义的折射定律和反射定律很容易实现反常反射和反常折射行为, 并给出了出现反常反射和反常折射的条件, 以此为基础可以实现对光波的随意控制. 依据广义的折射定律和反射定律分析了一维相位掩模板对光场传播行为的影响. 关键词： 超材料 相位突变界面 反射定律 折射定律     

Effects of dispersion and longitudinal chromatic aberration on the focusing of isodiffracting pulsed Gaussian light beam

Taking into account the dispersion and the longitudinal chromatic aberration (LCA) of the material of the lens, focusing of isodiffracting pulsed Gaussian light beam through single lens is analyzed. The smaller the cycle number of the isodiffracting pulsed Gaussian light beam is, the higher the order of the material dispersion should be considered.     

Light Pipe Line Beam Shaper

A light pipe based laser beam shaper is proposed as a low loss approach to transfer a Gaussian laser beam into a long line beam with uniform distribution along the line direction for the applications of illumination or material processing. A telecentric relay optics has been used for solving the radiometric issues in the wide angle optics. In addition, the length of the light pipe is used as a parameter for manipulating irradiance distribution at the outlet to compensate for the non-uniformity resulting from the partial reflection at the optical interface in the relay optics, so as to achieve a highly uniform line beam at the target plane. The proposed scheme provides an economical and versatile solution for the wide angle beam shaping problem.     

Simultaneous determination of the X-ray refractive index and the attenuation length from a single digitally registered radiograph of rectangular prisms

Prisms deflect and disperse X-rays due to refraction very similar to visible light. As X-rays are always attenuated while traversing material, the intensity distribution in the transmitted beam carries information about the prism transmission function. This study will show that sufficient information is contained in a single digitally registered radiograph from a rectangular prism, for deriving both the refractive index of the material and its attenuation length. The measured data can be prepared such that neither intensity fluctuations nor false light content in the incident beam will introduce systematic errors into the result. The strategy is thus very adapted, when single shot pictures are taken at X-ray sources with limited shot reproducibility. This technique is favourably be used at very grazing angles of incidence of the order of the critical angle for the prism material, when the beam deflection becomes significant. In such a geometry dimensional parameters, like sample thickness, do not affect the data analysis, which is particularly insensitive to even significant errors in the tip angle.     

Light deflection from ferroelectric domain boundaries

A new deflection phenomenon of light has been discovered in ferroelectric crystals that provides information about domain structures, their nucleation, and their dynamics: Illumination of a multi-domain crystal with a single light beam yields light patterns, if external electrical fields are applied. Deflection angles of up to ±8° are observed. We attribute this effect to light deflection from the boundaries of the domains. Besides providing a new method to study domains of any ferroelectric material, the method can be of practical importance for electro-optic beam scanning. PACS 42.25.Fx; 77.80.Fm; 77.84.Dy; 78.20.Jq     

圆柱体的空间圆锥光反射、折射与衍射

用准直或会聚激光束倾斜照射圆柱体时,其反射光、透射光(柱体透明时)、衍射光(柱体较细时)的叠加将形成以光束入射点为顶点的空间圆锥形光面(空间光锥),并且在垂直于柱体轴线方向的观察平面上投影成一圆形光环.空间光锥的形成与所选圆柱体材料及其粗细无关,只要其表面具有一定反射能力即可.空间光锥的锥角等于入射光束主光轴与圆柱体轴线夹角的2倍,与圆柱体和照射光束的直径大小及光波长无关.给出了对光纤及不同直径大小的玻璃和金属圆柱体的实验观察结果,并利用矢量图解法对其进行了详细地理论分析.进而得出,通常所谓单丝衍射图样,实际上是细丝的衍射和其表面的反射光场的叠加图样,对于透明细丝,还包括其透射光场的贡献.圆柱体的这种空间圆锥光反射和衍射原理有可能用于光束定位、成形、表面检测以及三维面形测量等 关键词： 圆柱体 空间光锥 投影光环     

Effect of laser beam incidence angle on the thermoelastic generation in semi-transparent materials

When a laser beam is absorbed in a semi-transparent material, a volume acoustic source is created owing to penetration of the laser beam inside the material and to thermoelastic transduction. Many experimental and theoretical studies have been conducted to better understand this ultrasound generation process with normal laser light incidence on the material surface. The purpose of this paper is to analyze the effects of the asymmetry caused by oblique incidence of a laser line source on the generation of acoustic waves in semi-transparent isotropic materials. Experiments on a glass plate demonstrate that such an obliquely incident laser light strongly affects bulk acoustic waves generation. Compressional and shear waves are enhanced and the loss of symmetry of the acoustic source causes asymmetrical behavior of the acoustic waves. Surprisingly, compressional-wave amplitude decreases whereas shear-wave amplitude increases in the region where the electromagnetic energy is refracted. This feature is explained by semi-analytical calculations.     

用高速显微摄影技术测量神龙一号上回喷靶材速度

用高速显微摄影技术对强流脉冲电子束轰击钽金属靶的过程进行了研究,获得了“神龙一号”加速器上靶材回喷过程的实验图像.实验表明,钽金属靶在强流脉冲电子束的作用下,有强烈的热释光现象产生,靶材的回喷粒子的轴向速度可达4.7 mm/μs.     

Simultaneous slow and fast light in C60 solution

Recently, many researchers have reported their work about sub- and superluminal propagation. And many experiments have demonstrated the group velocity transition between slow and fast light. In this letter, the authors reported simultaneous slow and fast light in a single light beam which could be explained by the photorefractive lens-like effect and the spatial dispersion qualitatively. In our experiment, a focused light beam at 532 nm normally incident upon a thin quartz cell full of C₆₀ solution and spatial diffraction rings were observed behind the cell. Recurring to a pinhole diaphragm, we measured the group velocity of light of different position on the diffraction rings. The experimental results demonstrated that slow and fast could exist in a single beam at the same time. We could acquire slow or fast light just by adjusting the position of the detector and keeping the experimental parameters, such as: modulation frequency and incident intensity, unchanged. Our experiment put forward a new way to control the group velocity in nonlinear optical material.     

Multistate polarization addressing using a single beam in an azo polymer film

Peculiar light-matter interactions can break the rule that a single beam polarization can address only two states in an optical memory device. Multistate storage of a single beam polarization is achieved using self-induced surface diffraction gratings in a photoactive polymer material. The grating orientation follows the incident light beam's polarization direction. The permanent self-induced surface relief grating can be read out in real time using the same laser beam.     

关于利用激光光束偏转法测量热扩散率的研究

本文介绍了激光光束偏转法测量材料热扩散率的原理,从理论上分析了光的粒子性和光的衍射限制了该方法对热扩散率的测量精度,指出了提高测量精度的关键在于提高信号对光束偏转的灵敏度为此给出了一种带有Ronchi光栅的迈克耳孙干涉仪的探测装置,从而使灵敏度提高了约5.3倍.     

左手材料中圆偏振光束的反常旋转特性研究

根据Whittaker标量势理论,建立了圆偏振光束的矢量传输模型.基于这一模型研究了圆偏振光束在左手材料中的反常旋转特性.通过分析光束偏振态、衍射对强度质心旋转特性的影响,发现圆偏振光束在左手材料中旋转方向反转并揭示其旋转角等于古伊相.采用分析横向能流的方法,揭示左手材料中反向的横向能流是导致反常旋转特性的主要原因.对圆偏振光束在左手材料中反常旋转特性的研究,有利于增强对左手材料中光束传输特性的认识. 关键词： 左手材料 圆偏振光束 旋转特性     

红外光学材料透过率温度特性测量方法

提出了一种变温条件下红外光学材料透过率测量评价方法。研究内容包括使用准直反射镜将红外光源变为平行光,通过斩波器变为脉冲光,再经滤光片选择波长;使用平面反射镜组与精密温控炉来获得变温条件下的双光路:测试光路与参考光路。使用前置放大电路和锁相放大器对红外微弱信号进行检测,根据两个光路的测量电压计算样品的透过率及透过率温度系数。计算机实现自动控制、采集与相关运算。该方法解决了变温条件下红外光学材料透过率测量中的实际应用问题,使光学材料参数检测从常规检测扩展到高温等极端条件,更接近于材料的实际使用条件,蓝宝石材料在波长5195 nm处,透过率高于10%,温度从室温到700℃的范围内,重复性优于0.2%。     

Diffraction-free and dispersion-free pulsed beam propagation in dispersive media

The diffraction of pulsed beams of light is formulated as an anomalously dispersive phenomenon. In a dispersive material, the effects of material group-velocity dispersion and diffraction on pulsed beam propagation can mutually cancel if the transverse profile of the pulse is suitably chosen.     

Generation of reflected second-harmonic light beam with inhomogeneous transversal distribution of polarization from the surface of chiral medium by normally incident Gaussian beam

A principle possibility of second harmonic generation (SHG) from the surface of a chiral medium by normally incident focused fundamental beam has been shown earlier, and the key features of this phenomenon (forbidden in a planewave approximation) have been outlined in [N.I. Koroteev, V.A. Makarov, S.N. Volkov, Laser Phys. 8 (1998) 532-535]. In our work we have obtained analytical expressions, which describe the distributions of intensity and polarization in the cross-section of a second-harmonic (SH) light beam. It is found that the polarization state drastically changes along the cross-section of the signal light beam. The polarization effects concerning the transversal inhomogeneous polarization distribution were studied in detail. It is shown that the measurement of the polarization state in certain areas of the SH beam cross-section gives us quantitative information directly about the medium material constants.     

Ultrafast optical beam deflection in a pump probe configuration

Propagation of a signal beam in an Al Ga As/Ga As waveguide multiple-prism light deflector is theoretically investigated by solving the scalar Helmholtz equation to obtain the dependences of the temporal and spatial resolvable characteristics of the ultrafast deflector on the material dispersion of Ga As including group velocity dispersion and angular dispersion,interface reflection,and interface scattering of multiple-prism deflector.Furthermore,we experimentally confirm that,in this ultrafast beam deflection device,the deflecting angle of the signal light beam is linear with the pump fluence and the temporal resolution of the ultrafast deflection is 10 ps.Our results show that the improvement of the temporal and spatial resolvable performances is possible by properly choosing the structural parameters and enhancing the quality of the device.     

Light-induced nonhomogeneity and gradient bending in photochromic liquid crystal elastomers

The recently reported opto-mechanical effect of some photochromic liquid crystal elastomers (LCEs) is studied. It is found that in such LCEs, material parameters such as the Young’s modulus and the stress-free strains will become nonhomogeneous under light irradiations. One may call them the light-induced functionally gradient materials. Analytical expressions for the dependence of the material parameters on the space variable and possibly on the time variable are obtained. Exponential dependence can be derived under certain approximations. As an example, the light-induced bending of a beam is studied. Two neutral planes are found in the beam. Thus, along the thickness of the beam, there are extensions in the upper and lower parts and contractions in the middle.     

Achromatic polarimeter

A polarimeter for measuring complete state of polarization of light in a wide spectral range is investigated. The light beam to be analyzed propagates through a continuously rotating first-phase plate; then through a continuously rotating second-phase plate; and, passing through a stationary linear polarizer, is incident on a detector. The time dependence of the intensity of the light beam that propagated though the polarizer is recorded. Fourier analysis of the periodic time dependence of the intensity yields the state of polarization of the light, which is characterized by four Stokes parameters. It is shown that the relation between the rotational velocities of the two phase plates and their thicknesses can be chosen such that the working range of the polarimeter would be limited only by the transparency range of the birefringent material of the phase plates, the working range of the linear polarizer, and that of the detector.     

Determination of carrier density dependent lifetime and quantum efficiency in semiconductors with a photoluminescence method (application to InGaAsP/InP heterostructures)

The light beam of a laser is focussed near the surface of a semiconductor sample. Thereby the excitation rate can be controlled precisely assuming a Gaussian intensity distribution of the beam. Measuring the recombination light intensity yields the quantum efficiency of the sample. By sinusoidal modulation of the excitation light and measurement of the resulting phase shift of the recombination light, the carrier density dependent lifetime is obtained. By evaluation of measured internal quantum efficiency and phase shift, Auger and radiative recombination coefficients are determined. The analysis takes into account the carrier density dependence of the radiative coefficient and shows that for most experimental conditions carrier diffusion can be neglected. In this case the analysis can be performed without numerical integration. Application of the method to quaternary InGaAsP material yielded values for Auger coefficient and radiative coefficients in accordance with published results.