Rotationally tunable two-beam interferometer with a fixed photosensitive element. Part I. Interferometer based on a beam-splitter cube

A two-beam interferometer based on a beam-splitter cube with a fixed photosensitive element is proposed. The interferometer is designed for generating interference patterns with a tunable period. The only type of motion resulting in a change in the period is interferometer rotation with respect to the source of the light beam. The greatest width of the range of convergence angle tuning is close to 50°, and possible values of this angle lie in the interval from 10 to 180°. The interferometer arms have identical lengths owing to its symmetry. The absence of adjustment elements ensures high stability of the instrument with respect to vibrations.     

Limiting characteristics of a rotationally tunable two-beam interferometer with a fixed photosensitive element

Results of calculations of the limiting characteristics of a rotationally tunable two-beam interferometer on the basis of a beam-splitter cube with fixed mirrors and a fixed photosensitive element are presented. The convergence angle is changed solely by rotating the beam source with respect to the interferometer. It is shown that the convergence angle can be varied in the interval from 46 to 166° with sufficiently wide light beams.     

Tunable holographic interferometer with a beam-splitting unit and fixed mirrors

This paper presents a holographic interferometer configuration with inclined fixed mirrors based on a beam-splitting unit in which the convergence angle of the partial beams is tuned only by rotating the interferometer relative to the radiation source. The continuous range of tuning is close to the maximum possible (0–180°). The path lengths of the interfering beams are automatically aligned due to the mirror symmetry of the system. The position of the axis of rotation providing minimal aperture limitations in almost the entire range of tuning is determined. A comparison is made with an alternative configuration based on a beam-splitter cube.     

Reconfigurable holographic interferometer with fixed mirrors

The configuration of a two-beam interferometer with fixed inclined mirrors for recording holographic gratings is described. The convergence angle of the partial beams is adjusted in the range from 0 to 180° by changing the angle of incidence of the primary beam on the entry edge of the beam-splitting cube without additional adjustment of the mirrors. The path lengths of the interfering beams are automatically aligned by the mirror symmetry of the system. The optimal kinematics of adjusting the convergence angle is found that allows working with beams of sufficiently large diameter in the whole range of adjustment. The interferometer is highly resistive to vibration due to lack of adjustment devices.     

一种滚转角和直线度同步干涉测量方法的研究

提出一种用于精密线性位移台滚转角和运动直线度同步测量的激光外差干涉系统。该干涉系统由一个Koster棱镜、角隅棱镜、分光镜、1/2波片、直角棱镜、1/4波片以及楔面棱镜和楔面反射镜组成。楔面棱镜作为测量运动直线度和滚转角的传感器固定在线性导轨上,当双频激光器的光射入干涉系统中后,形成空间对称的六光束测量信号。空间结构对称、系统共光路的特点使光学分辨率比普通的迈克尔逊干涉仪高一倍,光程死区达到最小。系统稳定性好,抗环境干扰能力强。光路对称使得增加或减小的光程变化相同,其他自由度引起的光程变化相互抵消,仅有运动直线度和滚转角的变化可以进入光程差,有效地排除其他自由度及阿贝误差的串扰,实现高精密测量。试验证明相互平行且不同频率的两束光在同一反射系统中发生运动直线度偏移和滚转角变化时,通过两束光携带的不同相位信息能直接得到运动直线度和滚转角的变化值。它不需要一条与行程同样长度的大反射镜作参考便能够实现高分辨率测量,简单实用,可直接溯源米定义。     

Four-point bisensitivity velocity interferometer with a multireflection etalon

A four-point bisensitivity velocity interferometer system for any reflector (VISAR) with a renovative delay etalon is proposed and demonstrated. In this interferometer, we introduce a new film-coating strategy to accurately measure small velocity with relatively short and cheap etalon. Laser pointing to the etalon is split into two beams with different incident angles with each beam going through the etalon in different path. The beam with the smaller incident angle is reflected three times before it leaves the etalon, while the other beam with larger incident angle goes through the etalon to and forth only once. The delay time of the laser beam with smaller incident angle is almost three times longer than that of the beam with larger incident angle. In the example of the laser with a smaller incident angle, the velocity per fringe of this interferometer can be reduced by approximately three times. The etalon is optimized so that four laser beams can be penetrated in the vertical direction at the meantime. With an etalon of 200 mm in diameter and 150 mm in length, a four-point bisensitivity velocity interferometer can achieve the velocity per fringe of 100 and 350 m/s fringe. A measurement has been successfully undertaken for the steel flyer driven by the explosive where the developed interferometer applies.     

Present Status of EUV Interferometer Development at the Research Center for Soft X-ray Microscopy

A new interferometer for extreme ultraviolet (EUV) radiation with a laser produced plasma (LPP) laboratory source is under construction. The LPP source is operated with a Sn solid rod target on which pulsed YAG laser is focused to produce high temperature plasma emitting EUV radiation. The source is equipped with a newly designed debris stopper protecting a condenser multilayer mirror from the particle debris of the target. The condenser mirror focuses the light onto an EUV beam - splitter to form transmitted and reflected paths for producing interference fringes of a sharing type. The optical configuration is of a common path based on a triangular path type with a focusing at the beam- splitter, which is enabled to produce fringes by a low coherence radiation with a standard optical quality beam - splitter. The fringes are recorded by an imaging plate with pixels as small as 25μm. The dynamic range of linearity in detection of the EUV light was found to be more than 10^4 with sensitivity of 10^4 photo ns/pixel, enough for the purpose of interferogram recording possibly with one laser shot.     

Process simulation and optimization of laser tube bending

A 3D thermomechanical finite element analysis model for laser tube bending is developed based on the software MSC/Marc. The processes of single- and multi-scan are analyzed numerically. The gradient and development of the temperature between the laser scanning side and the nonscanning side leads to the changing complexity of the stress and strain. Consequently, the length of the laser scanning side becomes shorter than that of nonscanning side after cooling. The length difference between both sides makes the tube produce the bending angle. The relationship between the number of scans and the bending angle is about in direct ratio. The bending angle induced by the first irradiated time is largest. Meanwhile, the finite element simulation is integrated with the genetic algorithm. Aiming at different process demands, corresponding objective functions are established. Laser power, beam diameter, scanning velocity, and scanning wrap angle are regarded as design variables. Process optimizations of maximum angle bending and fixed angle bending after single laser scan are realized. Groups of optimized process parameters can be obtained according to different optimization objectives. The bending angle can approach to the maximum when the laser power, spot diameter, scanning velocity, and scanning wrap angle are 381.24 W, 3.37 mm, 16.34 mm/s, and 123.1°, respectively. When the laser power, spot diameter and scanning velocity are 426.12 W, 4.9 mm, 14.31 mm/s respectively, a fixed angle bending can be achieved.     

An optical lever by using a mode-locked laser for angle measurement

A new concept of optical lever for angle measurement having an extended angular measurement range with a mode-locked laser as the light source, which is significantly extended from the conventional photodiode (PD)-type optical levers with a single frequency laser, is proposed. In the proposed concept, a collimated laser beam of the mode-locked laser is made incident to a grating reflector to generate a group of first-order diffracted beams from the grating reflector. Differing from a conventional PD-type optical lever employing a laser beam with a single frequency as the light source, the angle measurement range can be significantly expanded for the sake of the group of widely-spread first-order diffracted beams. In addition, the proposed optical lever has a potential of assuring the traceability of angle measurement by linking it to the optical frequency comb based on the mode-locked laser, which is employed as the national standard of time and frequency. In this paper, as a first step of this research, a mode-locked femtosecond laser is employed as the light source of the proposed optical lever. To distinguish each of the first-order diffracted beams generated with the combination of the mode-locked femtosecond laser and the diffraction grating having a grating period of 1.67 μm, a Fabry-Pérot etalon is employed in the setup of the optical lever to modulate the distance between two neighboring beams in the group of first-order diffracted beams. Experimental setups are developed, and basic experiments are carried out to verify the feasibility of the proposed optical lever.     

Nano-vibration measurements using the photoelectromotive force effect in the GaAs crystal

A broadband, nano-vibration measuring method based on the photoelectromotive force (photo-EMF) effect of semiconductor crystal is presented. A He-Ne-laser homodyne interferometer system is used as a light source and a GaAs crystal is used as a photodetector. The signal beam, which is modulated by the vibration, interferes with the reference beam, and a vibrating interference pattern is created on the surface of the GaAs crystal. Due to the photo-EMF effect, an alternating current signal, which relates to the vibration, is produced. We found the optimum parameters for the measurements by adjustments of the intensity ratio of the two beams, the angle between the beams and the interelectrode spacing on the GaAs crystal. The system can detect the vibration amplitude about several nanometers. The results of measurements of the vibrations of the PZT sample are well coincided with those obtained by TEMPO200 (Bossa Nova Technologies, America) system.     

三光束干涉仪参数分析及优化设计

从理想情况出发,得出了用周期为2p的光栅扫描时,由光电探测器接收到的三光束干涉光强分布式。从优化设计的角度求出了光栅的最佳参数以及干涉仪三束光的最佳光强之比;计算出了理想情况下仪器可能达到的精度以及有误差情况下的干涉条纹光强分布式;最后得出了合理的误差允差。     

基于荧光成像的准分子激光系统多路光束自动准直

研究了基于准直光束成像的准分子激光主振荡功率放大(MOPA)系统的多路光束自动准直,实现了激光在放大器中的多程放大及高的靶面指向精度。采用352nm He-Cd激光作为准直光源,提出了多光束感光屏同步接收与可见光CCD荧光成像相结合的复合图像采集技术,解决了自动准直系统多路激光的近场、远场图像获取问题。利用图像区域分割处理方法编制了准直信息处理软件,实现了对多光束的自动准直闭环反馈控制。最后,结合准分子激光MOPA系统中的预放大器光学设计进行了自动准直验证实验。结果表明:准直成像光强可调谐倍数为300,成像系统在放大器窗口处固有误差占放大器口径比例小于设计值1.08%,3路激光的自动准直时间为40s,完全满足放大器的几何填充和能量提取要求。     

High sensitivity all-fiber Sagnac interferometer temperature sensor using a selective ethanol-filled photonic crystal fiber

An all-fiber Sagnac temperature sensor based on 3?dB tapered coupling and ethanol selective-filled photonic crystal fiber was demonstrated theoretically and experimentally. The ethanol selectivity-filled photonic crystal fiber has noncircular symmetry and thus exhibits birefringence. The ethanol selective-filled photonic crystal fiber, acting as the sensing element, was inserted in a Sagnac loop interferometer to measure temperature. The output spectra of Sagnac interferometer applied different temperatures were measured and analyzed. Experimental results have shown the temperature sensitivity of the Sagnac interferometer is 1.65?nm/°C in the range of 25–33°C.     

工作波长为13.9nm的Laminar分合束光栅研制

目的：基于衍射光栅分合束元件的软X射线Mach－Zehnder干涉系统在惯性约束聚变,X射线激光等领域都有重要的应用前景。针对该干涉系统的特点设计、制作了工作波长为13.9nm的矩形分合束光栅。方法：利用全息曝光－离子束刻蚀工艺制作了特定参数的矩形光栅,利用长行程面型仪（LTP）对其线密度进行了测量,利用原子力显微镜测量其槽深与占宽比,利用国家同步辐射实验室（NSRL）U27实验站测量其衍射效率。结果：该矩形光栅的参数为线密度1000l/mm,槽深13±0.2nm,占宽比0.4±10%,Au膜厚度为40±0.5nm;在工作波长为13.9nm,81.2°入射时,其0级与-1级衍射光衍射效率乘积的最大值为8.6％,同时0级与-1级衍射效率亦接近,约为27％和30％。结论：测量结果充分证明矩形光栅作为13.9nm激光的分合束元件是能够获得高分合束效率(>7%),且矩形分合束元件易于制作。     

Cover slip external cavity diode laser

A 671 nm diode laser with a mode-hop-free tuning range of 40 GHz is described. This long tuning range is achieved by simultaneously ramping the external cavity length with the laser injection current. The laser output pointing remains fixed, independent of its frequency because of the cover slip cavity design. This system is simple, economical, robust, and easy to use for spectroscopy, as we demonstrate with lithium vapor and lithium atom beam experiments.     

基于保偏镜组的外差干涉测量几何误差分析

角锥棱镜由于本身缺陷会导致失偏效应。在平面镜外差干涉仪中,使用一种保偏反射镜组替代角锥棱镜,以减小外差干涉仪的非线性误差。根据这个平面镜外差干涉仪的基本光路图,基于偏振分光棱镜和角锥棱镜的基本光学特性,分析了平面镜外差干涉仪中3个偏振分光棱镜偏摆角、仰俯角和滚动角,保偏反射镜组中2个偏振分光棱镜之间的间距和角度,以及角锥棱镜的偏摆角和仰俯角等误差对干涉仪的影响。推导出外差干涉仪中各个光学元件的最大安装误差,并规定好其加工精度,确保外差干涉仪性能。     

光纤光栅空分光复用传感系统的研究

介绍了一种光纤光栅空分复用传感系统,并将光纤光栅的传感特性应用于结构健康检测系统中。宽带光源发出的光波进入光栅阵列时,利用光开关选通不同光路实现FBG空分复用传感系统。系统采用等腰三角形悬臂梁调谐装置对FBG进行挠度加载,利用非平衡M-Z干涉技术对传感信息进行解调,将包含被测应变信息的FBG波长信号转变成相位信号,从而得到被测应变的大小,成功地实现了空分复用传感。该系统可用于静态应变和动态应变的检测,具有高分辨力、大测量范围的特点,其传感分辨率为7.3 nε,灵敏度的实验值为0.82°/με。     

分光镜对外差激光干涉仪非线性的影响

外差干涉仪的非线性误差不仅由激光源的椭圆偏振态或者非正交线偏振态引起,也由非理想的光学器件引起,其中分光镜是一个重要的误差源。除了通常熟知的偏振漏光,还分析偏振分光镜中可能存在的另一个误差,即偏振分光的正交性,介绍这种误差和其他各种原因(包括激光源的椭圆偏振态或者非正交线偏振态)对外差干涉仪非线性误差的影响,给出检测和区分两类不同频率混叠误差的方法。通过试验证实,偏振分光镜的漏光误差对外差干涉仪非线性的影响通常是可以被忽略不计的。试验研究还发现,与传统的理论假设相反,非偏振分光镜比偏振分光镜对外差干涉仪的非线性误差有着更严重的影响。     

A proposed design for a polarization-insensitive optical interferometer system with subnanometric capability

A bidirectional, fringe-counting, two-beam interferometer system is described that can be used for precision length measurement with any laser source that is adequately coherent for the application. The two electrical phase-quadrature signals required for bidirectional electronic counting are obtained from photodetectors at the two interferometer outputs. A thin metal film design for the beam-splitter coating introduces the required phase difference of nearly 90° for both the perpendicular and parallel polarization components. Electronic alignment and control are performed by a system used to continuously monitor the signals produced from the outputs and automatically process these signals to achieve the optimum performance from the interferometer. Interferometers using the technique require a limited amount of optical alignment and all of the electronic adjustments are automatically controlled by the electronic system. These instruments are economical to manufacture and easy to apply in practice, readily achieving subnanometric accuracy in the measurement of changes in optical path.     

高精密滚转角测量干涉仪

现有的各种激光干涉仪可以方便地测量围绕垂直于直线位移方向的两个转角偏移,但是对于围绕运动轴的滚转角偏移,特别是对于大行程运动,缺乏有效的测量方法。针对各种高精密直线运动定位装置,设计一个新型的差分平面干涉仪,并采用一个楔面棱镜和楔面反射镜,组合成为一个几何空间对称四光路系统,构成新型的高精密滚转角激光干涉测量仪。它不需要与行程同长的大反射参考镜,但同样能实现高分辨率,而且简便实用,可以直接溯源米定义。试验证明,几何空间对称四光路滚转角干涉测量仪能够有效地排除其他自由度运动的干扰,利用它可以快速高效地测量各种精密直线位移运动的滚转角。使用普通的2π/360细分相位计,测量分辨率为1.1″,若使用2π/36 000的高精密细分相位计,滚转角的测量分辨率可达到0.01″。