二维金属光栅的矢量模式研究

用矢量模式场来描述二维金属光栅各层中的电磁场。由边界条件,推导出模式场方程组;借助反射透射系数阵递推算法,得出了方程组的解。这种矢量模式方法物理概念清晰且稳定收敛,可以处理任意偏振态平面波入射到二维亚波长金属光栅中的衍射问题。     

集成光栅干涉微位移测量方法

介绍了一种新型集成光栅干涉微位移测量方法,设计加工了微位移敏感芯片,并进行了初步的性能测试．敏感芯片利用硅-玻璃键合体硅工艺制作而成,在玻璃上制有金属光栅,光栅上方有由铝梁支撑的可动结构．实验系统由敏感芯片、半导体激光器、光电二极管以及相应的驱动、检测电路组成入射激光照射到光栅上产生衍射光斑,衍射光的光强随可动结构与光栅之间的距离变化,通过测量衍射光强的变化可以得到位移．测试实验结果表明,所制作的集成光栅干涉微位移敏感芯片可实现位移检测,最小可检测的位移约0．2nm．     

基于衍射光栅的二维纳米位移测量技术

提出了一种基于正交衍射光栅作为测量基准元件的二维激光干涉测量系统.利用正交光栅的空间对称级的衍射光进行干涉,基于多普勒效应,采用偏振检测的方法获得相位相差90°的干涉信号.通过光电检测把获得的正弦和余弦信号进行相位细分,系统可在平面二维方向上实现纳米级的分辨率.该系统相比其他干涉测量系统,测量结构紧凑,环境因素对其影响较小,可应用于较大行程的平面微位移精密检测.     

矢量腔光力系统中声子激光的研究

该文在传统的腔光力系统中引入了一组正交偏振基向量构成矢量耦合光力系统,并研究了其中的声子激光现象,发现偏振光的偏振角度可以有效调控声子激光的产生。研究发现,不同的线性偏振光对系统进行泵浦会出现不同强度的光力非线性相互作用,进而产生具有低功耗和易调控双重优点的声子激光现象,尤其是通过改变泵浦光的偏振方向可以连续调节声子激光的强度和阈值。与传统的声子激光方案相比,在不改变系统其他参数的情况下,可以通过调节光偏振有效地控制声子激光的产生。     

光折变Bi12SiO20晶体中的波耦合性质

研究在光折变Bi12SiO20晶体中二波耦合扩散全息记录的信号光能量增益和偏振态改变。在3种制备可得的晶体切割面上给出任意光栅取向的能量和偏振态耦合量的取值范围,分析了信号光能量增益和偏振态改变量分别达到最大值时各向同性和各向异性耦合的作用,此外研究旋光效应，压电及弹光效应在3种晶体切割面上对矢量波耦合的影响。     

光纤型偏振OCT 系统中光偏振特性的研究

建立了偏振光在生物组织中传播的模型,并利用该模型模拟了偏振光在生物组织中传播的过程,重建了多种偏振态输入光的情况下光偏振态在生物组织中的分布及生物组织的偏振特性模型.分析了光偏振度与光被生物组织散射次数的关系,阐明了由于偏振光在组织中传播,其偏振态逐渐改变而造成的偏振OCT 干涉计两臂光束失去相干性及偏振OCT 图像质量下降现象.通过分析斯托克斯(Stokes)矢量和穆勒(Muller)矩阵在光纤型偏振OCT系统中的应用,说明Muller 矩阵不受输入光偏振态的影响,因此它比Stokes 矢量更适用于光纤型偏振OCT 系统研究.     

纳焦飞秒激光在有机材料表面刻划微结构光栅的研究

使用振荡器产生的飞秒激光在透明有机材料PMMA表面进行了刻划微结构光栅的研究．通过理论分析得到了飞秒激光参数和平台移动速度对线宽的影响，进行了系统的加工实验，加工结果与理论分析基本吻合．在透明有机材料PMMA表面进行了多种光栅的刻划，并对刻划的光栅进行了衍射和色散测试，调整光栅的尺寸和排列方式，得到了形状各异的衍射图案。     

飞秒激光烧蚀材料表面产生纳米波纹结构的实验

利用飞秒脉冲激光烧蚀可以获得远小于激光中心波长（775nm）量级的周期条纹．通过多脉冲飞秒激光烧蚀Ni、Al、Cu、Ti和Si等材料表面的实验,得到材料表面产生光栅的周期均小于飞秒激光中心波长;采用对比实验,改变入射光的偏振特性,发现波纹周期方向随入射光偏振方向的改变而改变;不改变激光偏振态、脉冲能量为4．2J／cm^2时,沿波纹周期走向,发现平台移动速度为0．1mm／s时,可获得清晰的551nm的金属周期结构;最后应用上述实验结果,在铜片表面制备了长为几十微米、周期为551nm的微纳光栅结构。     

衍射测径中由不同偏振产生的系统误差

本文从Sommerfeld半无限大金属平面衍射的严格解得到狭缝平面的初始场分布,由Fourier变换给出两种偏振E和H的衍射公式。与传统的标量衍射公式相比较,在缝间距或丝径d较小时,仍能使用标量衍射理论的暗点法测量d的条件是:对狭缝,入射电磁场应为H偏振;对细丝,应使用E偏振入射场。     

衍射光栅的运动速度与多普勒频移信号的测量

一、前言利用激光多普勒效应进行气体液体和固体的速度测量,已在国内外得到广泛的重视和研究,并已将此新技术用于科研和生产。但是,通过测量激光的多普勒频移值△f,来求运动体的速度,其测速精度将受激光波长、接收方向及双光束夹角等换算因子精度的影响。衍射光栅多普勒频移信号△f,可由双光栅干涉系统产生,它所得到的多普勒信号和入射光的方向及光波波长均没有关系,只决定于光栅常数和光栅的运动速度。通过分偏振移相,还能得到四个90°相移的干涉信号,可直接用计数示波器和李沙育图形测量光栅的运动速度。因此,利用衍射光栅测量运动物体的速度     

Polarization-dependent diffraction efficiency of a photorefractive volume grating and suppression of this efficiency

In terms of refractive-index ellipsoid of a uniaxial crystal, the relationship between the diffraction efficiency of a volume grating and the polarization state of a readout beam is theoretically analyzed. The direction of a refractive light beam and the corresponding refractive-index modulation will both be changed by a variation of the polarization state. In the polarization state of the readout beam, which may lead to a strong variation in the diffraction efficiency of the volume grating. This kind of polarization-dependent diffraction efficiency of a volume grating in an anisotropic crystal is extremely disadvantageous for some applications. A method to suppress the polarization-dependent diffraction efficiency by use of double volume gratings is presented, and experiments with LiNbO3:Fe crystal are also demonstrated. The experimental results indicate that this method can well suppress the polarization-dependent diffraction efficiency of a volume grating. Furthermore, the diffraction properties of the double volume gratings are almost independent of the polarization state of the readout beam. The relative values of the diffraction peaks are calculated on the basis of the relationship between index modulation and the state of polarization. The experimental values are in good agreement with the theoretical analyses.     

Ellipsometry of diffractive insect reflectors

Scales on the wings of certain insects, such as Trichoplusia orichalcea, exhibit a surface micro structure resembling a fine diffraction grating. Diffraction of incident light by this structure is responsible for many of the optical properties of the wings of this moth, such as the metallic yellow color and the almost-specular reflection and polarization properties of the scattered radiation. It is shown that by the use of null ellipsometry the polarization characteristics can be used to obtain the optical constants of the scale material. Theoretical considerations and suitable experimental conditions are discussed and evaluated.     

Spectral polarization measurements by use of the grating division-of-amplitude photopolarimeter

The grating division-of-amplitude photopolarimeter (G-DOAP) is an instrument that exploits the multiple-beam-splitting, polarizing, and dispersive properties of diffraction gratings for the time-resolved measurement of the complete state of polarization of collimated broadband incident light, as represented by the four Stokes parameters as a function of wavelength across the spectrum. It is a compact, high-speed sensor that has no moving parts and is simple to install and operate. These characteristics make the G-DOAP well suited for in situ spectroscopic ellipsometry (SE) applications for monitoring and controlling thin-film processes. The design and performance of a prototype instrument are presented. Precise SE measurements, to +/-0.04 degrees in psi and +/-0.1 degrees in delta, are demonstrated in the 550-940-nm wavelength range.     

Effect of reconstruction beam polarization on the kinetics of anisotropic gratings in bacteriorhodopsin

Anisotropic gratings are recorded on bacteriorhodopsin films by two parallelly polarized beams, and the effect of the polarization orientation of the reconstructing beam on the diffraction efficiency kinetics is studied. A theoretical model for the diffraction efficiency kinetics of the anisotropic grating is developed by combining Jones-matrix and photochromic two-state theory. It is found that the polarization azimuth of the reconstructing beam produces a cosine modulation on the kinetics of the diffraction efficiency, being positive at the peak efficiency and negative for steady state. By adding auxiliary violet light during grating formation, the saturation of the grating can be restrained. As a result, the negative cosine modulation for the steady-state diffraction efficiency changes to a positive one. In addition, the steady-state diffraction efficiency is increased appreciably for all reconstructing polarization orientations.     

Polarization sensitivity of the SUMER instrument on SOHO

The Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument on the Solar and Heliospheric Observatory (SOHO) satellite is sensitive to the state of linear polarization of the incident radiation primarily owing to two optical elements, the holographic grating and the wavelength scan mirror. The large angle of incidence of light striking the scan mirror, which varies from roughly 73.3 degrees to 81.6 degrees (with respect to the mirror normal), causes the mirror to act as a linear polarizer. Similarly, the spectrometer grating operates at incidence angles between 16.7 degrees and 35.0 degrees , adding to the polarization effect at some wavelengths. Measurement and characterization of this polarization sensitivity as a function of wavelength were performed with the engineering model optics (scan mirror and grating) and synchrotron radiation, which is nearly 100% linearly polarized, from the Super Anneau de Collisions d'Orsay (SUPERACO) positron storage ring in Orsay. The polarization sensitivity or modulation factor of the SUMER instrument was found to be between 0.4 and 0.6, depending on the wavelength and the angle of incidence of light striking the scan mirror; this agrees with the calculated polarization properties based on the measured optical constants for the silicon carbide mirror and grating.     

Transmittance analysis of diffraction phase grating

In order to accurately analyze and design the transmittance characteristic of a diffraction phase grating, the validity of both the scalar diffraction theory and the effective medium theory is quantitatively evaluated by the comparison of diffraction efficiencies predicted from both simplified theories to exact results calculated by the rigorous vector electromagnetic theory. The effect of surface profile parameters, including the normalized period, the normalized depth, and the fill factor for the precision of the simplified methods is determined at normal incidence. It is found that, in general, when the normalized period is more than four wavelengths of the incident light, the scalar diffraction theory is useful to estimate the transmittance of the phase grating. When the fill factor approaches 0.5, the error of the scalar method is minimized, and the scalar theory is accurate even at the grating period of two wavelengths. The transmittance characteristic as a function of the normalized period is strongly influenced by the grating duty cycle, but the diffraction performance on the normalized depth is independent of the fill factor of the grating. Additionally, the effective medium theory is accurate for evaluating the diffraction efficiency within an error of less than around 1% when no higher-order diffraction waves appear and only the zero-order waves exist. The precision of the effective medium theory for calculating transmittance properties as a function of the normalized period, the normalized groove depth, and the polarization state of incident light is insensitive to the fill factor of the phase grating.     

A non-contact technique for determining the depth of zero-order gratings

Abstract

In this work we present a simple, non-contact method for characterizing the depth of deep zero-order diffraction gratings using standard visible optics. Form birefringence exhibited by zero-order structures alters the polarization state of light transmitted through them. The amount of change is dependent on several factors including the depth of the grating grooves. By recording the polarization changes of laser light transmitted through the sample we demonstrate how the depth of any grating with a known pitch may be determined. Results for many different gratings have been analysed and show good agreement with groove depths measured from scanning electron micrographs. From these results a universal relationship between the amount of polarization change and the depth of the grating grooves has been determined.     

Reduction of polarization-induced artifacts in grating-based spectrometers

An optical device that converts unpolarized light into a single polarization state is described. The device is based on a polarizing beam splitter that separates the two polarization directions. The beam splitter is combined with two pairs of equilateral prisms that are used to collimate the two beams in terms of both propagation and polarization directions. When it is used in combination with a blazed diffraction grating, this device is shown to effectively remove the polarization dependence of the first-order diffracted power. The device has an insertion loss of approximately 14% for purely s-polarized light. However, for unpolarized light incident upon the two gratings studied here, the increased throughput of the p-polarized component leads to an average relative gain in overall efficiency of 13%-19%, depending on the grating. In collimating the two polarization directions, the device may cause a reduction in spectral resolution for a rectangular entrance slit. As a result, the device is more likely to find use in spectrometers that have a circular aperture, such as that provided by an optical fiber.     

Band-selective optical polarizer based on gold-nanowire plasmonic diffraction gratings

We report a plasmonic diffraction grating device as a new kind of optical polarizer. This simple device consists of periodically distributed gold nanowires on top of a transparent glass substrate and is based on the strong polarization dependence of the particle plasmon resonance of the gold nanowires. A high-efficiency secondary diffraction in the same device enhances the polarization extinction ratio significantly. Linearly polarized spectrum in the red with a bandwidth of 53 nm is selectively picked up from the nonpolarized white light, where a polarization extinction ratio higher than 100 at about 650 nm has been achieved. The idea of plasmonic diffraction grating is important for exploiting new detection and sensor techniques.     

Nematic liquid-crystal polarization gratings by modification of surface alignment

The stylus of an atomic force microscope is used to scribe preferred directions for liquid-crystal alignment on a polyimide-coated substrate. The opposing substrate that comprises the liquid-crystal cell is rubbed unidirectionally, resulting in a twisted nematic structure associated with each micrometer-sized pixel. The polarization of light entering from the uniformly rubbed substrate rotates with the nematic director by a different amount in each pixel, and each of the two emerging polarization eigenmodes interferes separately. Two examples are discussed: a square grating that allows only odd-order diffraction peaks and a grating that combines rotation with optical retardation to simulate a blazed grating for circularly polarized light. The gratings can be electrically switched if used with semitransparent electrodes.