外差干涉仪中偏振分光镜对测量精度的影响

为了提高激光外差干涉的测量精度,必须明确偏振分光镜(PBS)对激光外差干涉测量精度的影响.基于激光外差干涉非线性误差产生机理,建立了PBS对非线性误差一次谐波和二次谐波的综合影响模型.理论分析表明,选用偏振透射率稍弱、偏振反射率强的PBS有利于减小非线性误差.在激光器出射的两激光束存在5°非正交误差情况下,当PBS的反射率理想时,透射率从1减小到0.90,非线性误差由4.41 nm减小到4.19 nm.同时,通过调整旋转角度可以补偿非线性误差一次谐波.在PBS存在5°旋转角度误差情况下,当PBS的反射率理想时,PBS的透射率从1减小为0.90,非线性误差一次谐波从4.41 nm减小到2.56 nm.     

偏振分光镜旋转角度误差的确定

偏振分光镜存在旋转角度误差是引起激光外差干涉非线性误差的来源之一.提出了一种确定激光外差干涉偏振分光镜旋转角度误差的方法.通过分析偏振分光镜旋转角度误差在其它条件下对激光外差干涉非线性误差的影响,得出偏振分光镜存在的旋转角度误差将极大地增加非线性误差的一次谐波,但改变二次谐波很小.对光电接收器输出信号进行频谱分析,分离出激光外差干涉非线性误差的一次谐波和二次谐波,通过测量非线性误差二次谐波相对测量信号的大小,通过应用非线性误差二次谐波幅度比值与偏振分光镜旋转角度误差之间的模型,确定偏振分光镜旋转角度误差.实验结果表明,应用该方法能够得到偏振分光镜的旋转角度误差,从而为调整偏振分光镜提供了实验依据.     

波片和偏振片对外差干涉仪非线性的影响

为了减小外差干涉仪的非线性误差,必须明确波片和偏振片对非线性误差的影响机理。通过理论分析和试验发现,波片和偏振片位于偏振分光镜之前和之后对非线性的影响是不同的。如果把有误差的波片和偏振片放置在偏振分光镜前面,其误差将100%地引入非线性。如果将相同的这些光学元件安装在干涉仪里面,有可能影响非线性,但通常在高阶误差范围内。     

光学倍频影响激光外差干涉测量精度的机理

为了同时提高激光外差干涉测量的分辨力和精度,必须深入分析光学倍频对激光外差干涉测量精度的影响机理。在此基础上,建立了光学倍频相位测量模型,从理论上证明,光学倍频能够实现对激光外差干涉信号的细分,提高测量分辨力。光学倍频改变非线性误差的相位而使非线性误差减小,但同时改变了激光干涉多普勒频移的v/c平方项,使得残余累计误差增大。仿真结果表明,光学N倍频使非线性误差减小到原来的1/N,但使残余累计误差增大N2倍。因此,光学倍频仅适用于低速测量的场合。     

透射式外差椭偏测量及非线性误差分析

结合激光外差干涉法和透射式椭偏测量原理,研究了一种快速、高精度测量纳米厚度薄膜光学参数的方法．给出了光学系统设计和理论分析,使用两个声光调制器产生20kHz的差频,直接比较平行分量和垂直分量外差信号的幅值和相位,得到所需要的椭偏参数．光束偏振态的椭圆化及偏振分光不完全所引起的非线性误差是影响纳米薄膜测量精度的主要因素,推导出椭偏参数非线性误差的近似解析表达式,计算结果表明由此导致的膜厚测量误差可达几个nm,相对而言,激光器和反射镜等器件产生的光束椭偏化是其主要原因．     

单频激光干涉仪非线性误差修正方法

提出了一种谐波分离的干涉仪信号处理方法,利用傅里叶级数对校准信号进行最小二乘拟合得到修正模型.该方法适合于消除干涉信号中引起非线性误差的各种谐波成分.通过将修正分为初始相位计算和精确相位计算,可以使单频激光干涉仪的非线性误差修正达到最优化.模拟验证结果表明,当噪音信号幅度为基波信号幅度的5%时,残余误差的幅度约为±1 nm;而当噪音为0.5%时,残余误差约为±0.1 nm.     

高加速度超精密激光外差干涉测量模型

为了精确地描述激光外差干涉在高加速度超精密测量中加速度对位移测量精度的影响机理与规律,建立了高加速度超精密激光外差干涉位移测量模型.通过分析测量棱镜三维运动对多普勒频移的影响,推导出高加速度激光外差干涉位移测量模型.理论分析和仿真实验表明,当测量加速度为9m/s2,匀加速运行的位移为500mm时,由于加速度变化引起的相对论性效应对测量精度的影响为5nm.高加速度超精密激光外差干涉位移测量模型的建立,可提高激光外差干涉在高加速度超精密测量中的测量精度,为激光外差干涉在高速和超高速测量领域的应用提供了理论依据.     

斜波调频合成外差干涉相位检测非线性分析

目的　分析半导体激光器斜波调频合成外差干涉拍频频率变化对干涉相位的影响 .方法　从频域用计算机进行理论上的仿真 .结果　拍频频率偏离斜波调制电流频率整数倍时 ,会产生随干涉相位输出以π为周期呈正弦变化的非线性误差 .结论　根据拍频频率的变化 ,动态调节调制电流幅度可消除该非线性误差     

斜波调频合成外差干涉相位检测非线性分析

目的 分析半导体激光器斜波调频合成外差干涉拍频频率变化对干涉相位的影响。方法 从频域用计算机进行理论上的仿真。结果 拍频频率偏离斜波调制电流频率整数倍时，会产生随干涉相位输出以π为周期呈正弦变化的非线性误差。结论 根据拍频频率的变化，动态调节调制电流幅度可消除该非线性误差。     

外差激光干涉仪非线性的细分和消除

通过理论推导得到一个消除外差激光干涉仪非线性的理论,只要改变干涉仪的结构,也就是增加光程倍数,就可以减小激光干涉仪的非线性误差。实验证明,这个方法可以有效地减小双频激光干涉仪的各种非线性误差,不论这个误差是一阶的还是二阶的,也不论是什么原因引起的。它不仅适应于科学实验研究,而且也适应于工业精密测量应用,对纳米测试技术的发展具有实际意义。     

Measuring the polarization characteristics of birefringent optical fibers using an interference technique

A simple method based on the interference of coherently excited modes is proposed for measuring the orientations of birefringence axes and determining the level of polarized mode excitation in single-mode birefringent fibers. The exact determination of these characteristics is achieved by introducing the dimensionless coefficients of modulation and transmission dependent on the analyzer rotation angle. The proposed technique, in contrast to the conventional methods, does not require the use of special excitation conditions at the fiber entrance.     

Flat-field postobjective polygon scanner

A general two-dimensional ray-trace analysis is presented for the motion of a geometric focal point over a flat surface provided by a postobjective rotating polygon laser beam scanner. The exact defocus equation is derived for any value of the neutral scan position deflection angle and the polygon rotation angle. The scan nonlinearity is derived for the special case of a zero neutral scan deflection angle. Geometric parameters were found that reduce the peak-to-peak defocus by more than an order of magnitude from that found in previous design approaches. Conditions were also found that reduce scan nonlinearity to less than 2 × 10(-4). Practical limitations, such as large polygons and beam obscurations, encountered in the implementation of postobjective scanning are discussed.     

Anisotropic third-order optical nonlinearity of a single ZnO micro/nanowire

We report a systematic study about the anisotropic third-order optical nonlinearity of a single ZnO micro/nanowire by using the Z-scan method with a femtosecond laser. The two-photon absorption coefficient and nonlinear refraction index, which are measured as a function of polarization angle and sample orientation angle, exhibit oscillation curves with a period of π/2, indicating a highly polarized optical nonlinearity of the ZnO micro/nanowire. Further studies show that the polarized optical nonlinearity of the ZnO micro/nanowire is highly size-dependent. The results indicate that ZnO nanowire has great potential in applications of nanolasers, all-optical switching and polarization-sensitive photodetectors.     

Polarized second harmonic response of square, hexagonal and random arrays of gold metallic nanocylinders

The vertically and horizontally polarized second harmonic responses from arrays of gold metallic nanocylinders with different two-dimensional spatial organization, namely square, hexagonal and random arrangements, have been determined in transmission as a function of the input fundamental polarization angle. The results demonstrate that the second harmonic response is incoherent, resulting from the breaking of the centrosymmetry of the shape of the nanocylinders by surface defects. As a result, no effect from the geometrical arrangement of the nanocylinders on the substrate is observed.     

Mirrorless optical bistability in a semiconductor-doped-glass plate as a result of oblique incidence

A procedure to obtain optical bistability in a third-order nonlinear film (or parallel plate) of low refractive index without any external mirrors is investigated both theoretically and experimentally. If an s-polarized light is incident obliquely at a large angle of incidence on the film, the generation of optical bistability can be expected because of the resulting increase in the reflectivity at the surfaces. Arigorous analysis of the stationary transmission characteristics of the nonlinear film is done for both positive and negative nonlinear coefficients with a plane-wave model. In the experimental demonstration, a CdS(x)Se(1-x)doped glass (Hoya Y-52) plate and a cw Ar(+) laser are used as the nonlinear material and the light source, respectively. It is shown that three operations of optical bistability, optical limiting, and differential gain can be easily obtained through adjustment of the angle of incidence as an initial detuning. The measured nonlinearity is thermal, and the magnitude and sign of the nonlinear refractive index are determined.     

Measurement of refractive-index change at a liquid-solid interface close to the critical angle

We measured the refractive-index change on a liquid sample, using the reflection of a polarized Gaussian laser beam close to the angle of total reflection. We applied this technique to a solution of nickel (ii) phthalocyanine tetrasulfonated (NiPTS) in water-ethanol (1/1 v/v), in which the nonlinearity of the refractive index is due to optically induced thermal effects. We show that close to the angle of total reflection the sensitivity of this technique is four times bigger than at normal incidence.     

Mueller matrices and information derived from linear polarization lidar measurements: theory

A Mueller matrix M is developed for a single-scattering process such that G(theta, phi) = T (phi(a))M T (phi(p))u, where u is the incident irradiance Stokes vector transmitted through a linear polarizer at azimuthal angle phi(p), with transmission Mueller matrix T (phi(p)), and G(theta, phi) is the polarized irradiance Stokes vector measured by a detector with a field of view F, placed after an analyzer with transmission Mueller matrix T (phi(a)) at angle phi(a). The Mueller matrix M is a function of the Mueller matrix S (theta) of the scattering medium, the scattering angle (theta, phi), and the detector field of view F. The Mueller matrixM is derived for backscattering and forward scattering, along with equations for the detector polarized irradiance measurements (e.g., cross polarization and copolarization) and the depolarization ratio. The information that can be derived from the Mueller matrix M on the scattering Mueller matrixS (theta) is limited because the detector integrates the cone of incoming radiance over a range of azimuths of 2pi for forward scattering and backscattering. However, all nine Mueller matrix elements that affect linearly polarized radiation can be derived if a spatial filter in the form of a pie-slice slit is placed in the focal plane of the detector and azimuthally dependent polarized measurements and azimuthally integrated polarized measurements are combined.     

Angle dependent optical properties of polymer films with a biomimetic anti-reflecting surface replicated from cylindrical and tapered nanoporous alumina

Anodic porous alumina nanostructures have been fabricated with tapered and cylindrical pores with a spacing of 100 and 200 nm and depth of 180-500 nm. The porous nanostructures were replicated into polymer films to create a moth-eye anti-reflecting surface by a roll-to-roll UV replication process. The angle dependent optical transmission of the resulting polymer films exhibited up to a 2% increase in transmission at a normal angle and up to a 5% increase in transmission at a 70° angle of incidence to an equivalent film with a surface replicated from polished aluminum. No significant difference was observed between the optical performance of moth-eye surfaces formed from cylindrical and tapered nano-pores.     

Certain methods for eliminating errors due to nonlinear scanning in photo-pulsating instruments

Conclusions The discussed methods for controlling the scaling-pulse frequency as a function of the scanning diaphragm rotation angle serve to eliminate one of the basic errors of photo-pulsating gauges, which is due to the nonlinearity of scanning, and to develop several designs of gauges of the above class for work under different technological conditions.