纳米精度外差干涉仪非线性漂移的研究

在纳米精度外差干涉仪中，由于非线性温度漂移，成为外差干涉仪实现纳米精度测量的重要误差源。本文对差动干涉仪的理论分析得出如下的结论，干涉仪中除了测量光路和参考光路以外，还存在参考光误差分量和测量光误差分量的额外光路，从而引和了干涉混叠，产生非线性漂移：１／４波片的相位延迟量误差和安装是引入非线性漂移的主要因素，其影响程度是一阶的，提高波片对加工精度，并尽量减少其级数可降低非线性漂移。     

纳米分辨率外差干涉信号处理电路相位畸变的实验研究

外差干涉是实现纳米精度长度测量的重要手段。采用电子倍频、混频、高频计数的方法可处理外差信号实现亚纳米分辨率,具有电路简单、能计大数的优点,但会引入电子信号的相位畸变,引入测量的动态误差。本文通过理论和实验分析了这一误差,表明在电子倍频中锁相环引起的相位畸变仅在亚纳米量级,但在混频环节中带通滤波器引入的相位畸变则可达几纳米,引入较严重的误差。本文通过采用低频差横向塞曼激光器产生３２０ｋＨｚ的外差信号,并采用ＦＰＧＡ技术实现倍频后的高频率信号直接计数,省略混频环节,从而实现了高测量分辨率并避免了这一误差。     

一种基于光学倍乘原理的绝对距离干涉测量系统

介绍了一个基于光学倍乘原理的绝对距离干涉测量系统。系统包括两个干涉仪:采用半导体激光器作为光源的定位干涉仪和测量位移的外差干涉仪。介绍了光源的选择,系统的设计以及信号的采集和处理方案。采用这套绝对测量系统,可以实现长度为2m以内的绝对距离测量,定位精度可以达到±0.5μm。     

寄生虚反射对外差干涉椭偏测量的影响

研究了一种采用横向塞曼激光器并且没有任何运动部件的外差干涉椭偏测量系统。由非理想的激光源、偏振分光镜等器件所产生的非线性误差,是影响纳米测量精度的主要因素。采用琼斯矢量法,分析并建立了光学系统寄生虚反射所引入的误差模型,讨论了虚反射对误差漂移的影响。在不考虑其它误差因素的前提下,同一光路内部产生的同频率虚反射波对测量结果没有影响;而不同频率的参考光束与测量光束之间的交叉虚反射所产生的膜厚测量误差为亚纳米量级。讨论了消除和抑制虚反射误差的方法。     

在线测量表面粗糙度的共光路激光外差干涉仪

一种新型的、用于在线测量表面粗糙度的激光外差干涉仪已研制完成。该仪器体积小（２５ｃｍ×２０ｃｍ×１０ｃｍ）、抗外界环境干扰能力强。仪器以稳频半导体激光器作为光源。共光路设计,使测量光和参考光沿同一路径入射到被测表面上。计大数和测小数周期相结合的外差信号处理方法,实现了大的动态测量范围和很高的测量分辩率。同时还采用了全反射临界角法进行自动聚焦。该仪器的纵向和横向分辨率分别为０．３９ｎｍ和０．７３μｍ;自动聚焦范围为±０．５ｍｍ,在焦点±２５μｍ范围内,聚焦精度为１μｍ;８０分钟内整机稳定性：３σ＝１．９５ｎｍ。     

光学超外差法小平面角精密测量

文本用纵向塞曼双频稳频激光器作光源,提出了一种光学超外差法小平面角的精密测量方法.此方法采用相位干涉测量技术,测角灵敏度可达0.002”.优于其他平面角测量仪的测角灵敏度.     

光学纳米测量方法及发展趋势

综述了光学方法中以频率跟踪方法、外差干涉仪、调频干涉仪、偏振干涉仪和光学光栅为代表的光学纳米测量方法。分析了它们的发展状况以及各自特点,指出建立适合于纳米测量的纳米环境是目前亟待解决的关键性问题,给出了光学纳米测量方法的发展方向和在设计测量系统时应该注意的问题     

跨尺度亚纳米分辨的可溯源外差干涉仪

提出了一种能够实现跨尺度测量具有亚纳米分辨力的可溯源外差干涉仪,利用小型化碘稳频532 nm激光器,将激光频率溯源至国际计量委员会推荐的复现米定义谱线之一的R(56)32-O(a10)上;使用双频激光空间分离的设计方法,抑制了双频激光混叠引起的测量位移非线性误差,补偿了光纤与声光调制器引入的相位噪声;通过高精度的相位测量技术,使相位测量分辨率达到了0.017°.干涉仪的不确定度评估结果显示,100 mm的量程内,其不确定度达322 pm,实现了跨尺度亚纳米分辨力可溯源的位移测量.     

横向塞曼激光器

横向塞曼激光器(TZL)的优异特性是:可同时产生两个垂直偏振的线偏振光,二者之间的频差从几十千赫到几百千赫(取决于磁场强度、谐振腔的各向异性和激活介质的非线性),频差连续可调;具有高的频率稳定度和频率再现度.因此,它在精密干涉计量,晶体旋光性和双折射的检测,多普勒测速等方面有广泛应用前景. TZL的工作原理是基于横向磁场(磁场方向垂直于光的传播方向)下的反常塞曼效应和激光谐振腔的各向异性.原子的发射光谱在磁场作用下发生分裂.在没有谐振腔的作用时,沿光的传播方向可接收到三种线偏振光:　　和　　,它们分别对应于磁量子数之差…     

外差式激光干涉仪光学读出的两种新算法的设计与实现

纳米级和皮米级激光测距是光学技术中的重要一环,同时也是深空引力波探测实验所必须的技术。德国汉诺威的爱因斯坦研究所为此提出并实现了一种基于相位深度调制技术的外差式激光干涉仪,作为LISA计划测距系统的后备方案,在数值处理过程中使用了Levenberg-Marquardt非线性拟合方法作为干涉仪光学读出算法。探讨并展示了另外两种新的外差干涉仪光学读出拟合算法。第一种算法采用近似并迭代的数值方法将拟合过程分为两次迭代:第一次估算干涉仪的调制深度和调制相位,第二次线性迭代拟合干涉仪的相位和振幅。另外一种算法首先利用离散傅里叶变换计算频谱,然后从频谱中拟合出干涉仪的调制相位,之后采用高斯-牛顿迭代方法线性拟合调制深度、相位和振幅。在空气中长时间运行的结果显示,第一种拟合算法的连续测距误差小于0.24nm,第二种算法的误差在0.19nm左右,比原来的非线性拟合算法分析得到的误差小了5～6倍。     

基于激光外差技术的高分辨率整层大气透过率测量

激光外差技术是一种高灵敏度的光谱探测技术,利用该技术研制的装置易于集成化小型化,可以进行地基或星载的地球大气或天文观测。基于激光外差光谱测量技术,结合自研的太阳跟踪仪建立了一套高分辨率整层大气透过率测量系统,系统分辨率约为0.006 cm-1。该系统利用太阳光和红外激光在非线性探测器中进行光学混频,通过对获取的混频信号进行电子学滤波和平方率探测,获得了高光谱分辨率的外差信号。采用Langley-plot定标法对测量系统进行定标,获取了仪器标定常数和对应的大气总光学厚度,实现了中红外波段整层大气透过率的实时测量。同时,将实测整层大气透过率与MODTRAN5.0软件仿真计算的结果进行对比分析,两者的一致性较好。分析表明该测量系统具有很高的分辨率并且性能稳定可靠,在大气科学、天文观测和激光大气传输等研究领域具有广阔的应用前景。     

4.4 μm中红外激光外差光谱探测技术研究

在国内首次报道以窄线宽的4.4 μm外腔量子级联激光(QCL)作为本地振荡光源,黑体作为辐射光源的激光外差光谱实验装置的建立和测量工作。激光外差光谱是一种高灵敏度的光谱探测技术,并可以用于发展一种小型的光谱探测系统,进行地基或星载的地球大气或天文观测。介绍了激光外差的基本理论、装置的建立和实验测量工作。此激光外差光谱实验装置采用4.4 μm外腔量子级联激光,出光功率高达180 mW,在4.38～4.52 μm间连续可调,具有很宽的光谱调谐范围,能实现CO₂,CO和N₂O等大气重要分子的同时测量。通过开展不同压力下CO₂气体的激光外差光谱测量,对激光外差光谱实验装置的性能进行了评估。目前该激光外差系统的信噪比达到86,低于散粒噪声极限条件的理论计算值287,系统的光谱分辨率约为0.007 8 cm-1,能满足较窄线宽条件下的高分辨率激光外差光谱的测量。分析结果表明,中红外激光外差光谱系统具有很高的瞬态信噪比及光谱分辨率,在高精度测量大气温室气体的柱浓度和温室气体垂直廓线分布方面具有广阔的应用前景。     

Hybrid measurement system including optical heterodyne and laser microscopy functions using an acoustooptic deflector

The construction of a hybrid measurement system for measuring lateral and vertical dimensions and its applications to industrial inspection are described. This system uses an acoustooptic deflector, and includes optical heterodyne, confocal and non confocal laser scan microscopy functions in one and the same optical device. These functions are used individually or collectively depending on the purpose of the measurement. For example, by using the optical heterodyne and non confocal microscopy functions at the same time, lateral and vertical dimensions can be measured simultaneously.     

用转移矩阵法研究LNN型非线性平面光波导

用转移矩阵法数值分析了芯区和衬底为非线性介质、覆盖层为线性介质结构平面光波导的传播特性,包括TM的模场分布和功率与有效折射率之间关系的分析.解析地表达了模式本征方程和功率分布,对非线性介质中电场强度与介质非线性系数的关系进行了研究.计算结果表明,TM的模场分布和功率与有效折射率及介质的非线性系数有关.     

用塞曼双频激光器作光源的一种新颖长扫描表面的仪器设计

本文报道一套光学结构用于同步辐射反射镜表面轮廓高精度大面积的测量。采用了光学外差测量与接收技术,以伺服聚焦双折射透镜组分离“o”光与“e”光的聚焦区域,并再共轴组合比较其相位差,从而获得表面起伏的误差值。线性运动的测量工作台使镜面可测量范围从数微米到一米,而最小起伏量及曲率可达很高的测量精度。     

Raman heterodyne detected magnetic resonance: II. Magnetic transitions of NV centre at level anticrossing region

In the preceding paper [1] we reported both cw and coherent transient measurements carried out in EPR and NMR transitions within the³A ground state of the nitrogen-vacancy centre in diamond using the Raman heterodyne detection technique. In this paper we use these measurements to characterise the nuclear magnetic transitions near a level anticrossing situation. The level anticrossing causes a mixing of the electronic spin and nuclear spin wave functions which results in a greatly enhanced NMR transition moment. The amount of mixing not only affects the dipole moment but, correspondingly, the characteristic relaxation times. In this paper we report the measurement of these parameters in the nitrogen-vacancy centre as a function of applied Zeeman field strength and analyse the results using the spin Hamiltonian formalism. Furthermore, combined with the particular features of the Raman heterodyne technique, such a system represents an ideal testing ground for the nonlinear behaviour of strongly driven transitions. Some results are illustrated, including dynamic Zeeman splitting and gain without inversion.     

Heterodyne polarimetry for mapping defects in lithography masks

A new optical technique based on the heterodyne polarimetry is developed for fast inspection of uniformity of lithography masks in semiconductor industry. Sub-wavelength periodical structure of a sample acts as a wire-grid polarizer, making both the amplitude and phase of the reflected laser beam dependent on geometrical dimensions and optical properties of the mask pattern. The heterodyne technology based on the cross-polarized two-frequency Zeeman laser is used to simultaneously measure the amplitude and the phase of the reflected laser beam. A two-dimensional map of spatial variations can be obtained via point-by-point scanning of the sample. The technique is applicable not only to exact periodical structures like diffraction gratings, but also to double-periodical patterns consisting of large number of periodically distributed small areas of sub-wavelength gratings. Theoretical background, simulation, and experimental results are presented.     

Polarized optical coherence imaging in turbid media by use of a Zeeman laser

A method that uses a Zeeman laser in conjunction with a Glan-Thompson analyzer to image an object in a turbid medium is proposed. A heterodyne signal is generated only when the scattering photons are partially polarized, and the spatial coherence is not seriously degraded after the signal propagates in the turbid medium. A system combining polarization discrimination with optical coherence detection to image the object in a scattering medium is successfully demonstrated. The medium is a solution of polystyrene microspheres measuring 1.072 mum in diameter suspended in distilled water contained in a 10-mm-thick quartz cuvette. The advantages of this optical system, including better selectivity of the weak partially polarized scattering photons and better imaging ability in higher-scattering media, are discussed.     

A phase sensitive optical rotation measurement in a scattered chiral medium using a Zeeman laser

A novel circular polarized optical heterodyne interferometer using a Zeeman laser to measure optical rotation both in nonscattered and scattered chiral medium is proposed. A pair of correlated orthogonal circular polarized light waves of different temporal frequency propagating in the chiral medium at different speed is studied. This results in phase retardation between circular polarized light waves of which the phase difference is proportional to the optical rotation angle of a linear polarized light in a chiral medium. In the mean time, two orthogonal circular polarized light waves can be treated as a circular polarized photon pair that is able to reduce the scattering effect in a scattered chiral medium. Then the optical rotation angle can be measured in the scattering medium. In addition, a common-path configuration with respect to circular polarized light waves immune the background noise. This further improves the sensitivity on optical rotation measurement based on phase difference detection.