Sinusoidal phase-modulating laser diode interferometer for measuring angular displacement

We propose a sinusoidal phase-modulating laser diode interferometer for measuring small angular displacement. The interferometer is based on a Fabry-Perot plate. It has a simple structure and is insensitive to external disturbance. Sinusoidal phase-modulating interferometry is used for improving the measurement accuracy. A charge-coupled device (CCD) image sensor is used for measuring the distance between the reflected beams from two faces of the Fabry-Perot plate. From the distance, the initial angle of incidence is calculated. Compared with Michelson interferometers and autocollimators, this interferometer has the advantage of compact size and simple structure. The numerical calculation and experimental results verify the usefulness of this novel interferometer. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

Real-time far distance micro-vibration measurement using an external cavity semiconductor laser interferometer with a feedback control system

An external cavity semiconductor laser interferometer used to measure far distance micro-vibration in real time is proposed. In the interferometer, a single longitudinal mode and excellent coherent characteristic grating external cavity semiconductor laser is constructed and acted as a light source and a phase compensator. Its coherent length exceeds 200 meters. The angle between normal and incidence beam of the far object is allowed to change in definite range during the measurement with this interferometer, and this makes the far distance interference measurement easier and more convenient. Also, it is not required to keep the amplitudes of the first and second harmonic components equal, and then the dynamic range is increased. A feedback control system is used to compensate the phase disturbance between the two interference beams introduced by environmental vibration.

用于大范围高精度实时位移测量的半导体激光干涉仪

现有的半导体激光干涉仪存在测量精度与测量范围的矛盾。本文提出一种新的实时位移测量半导体激光干涉仪，并分析了干涉仪的测量原理。首先提出一种新的解相算法，它通过两路实时相位探测电路从干涉信号中得到待测量相位，消除了光强波动、初始光程差、电路放大倍数、调制深度、Bessel函数等参数对测量精度的影响，提高了测量精度。其次，提出一种扩大测量范围的技术，并用解包裹电路得到真实相位和待测量的位移, 将测量范围从半个波长提高到几个波长。在实验中，测得喇叭的峰峰值为2361.7nm，重复测量精度为2.56nm，测量时间为

实时测量表面形貌的正弦相位调制半导体干涉仪

提出一种实时测量表面形貌的正弦相位调制半导体激光干涉仪。利用实时相位检测电路，从正弦相位调制干涉信号中解出被测量物体表面形貌的相位。在实验中，测量了楔形光学平板的表面形貌，对表面形貌上的60

Measurement of the wavefront of a laser diode system for intersatellite communication by a Jamin double-shearing interferometer

The frame of a laser diode transmitter for intersatellite communication is concisely introduced. A simple, novel and visual method for measuring the diffraction-limited wavefront of the transmitter by a Jamin double-shearing interferometer is proposed. To verify the validity of the measurement, the far-field divergence of beam is additionally rigorously analysed in terms of the Fraunhofer diffraction. The measurement, the necessary analyses and discussion are given in detail. By directly measuring the fringe widths and quantitatively interpreting the interference fringes, the minimum detectable wavefront height (DWH) of the wavefront is only 0.2 gimel (the distance between the perfect plane wavefront and the actual wavefront at the transmitting aperture) and the corresponding divergence is only 65.84 mu rad. This indicates that the wavefront approaches the diffraction-limited condition. The results show that this interferometer is a powerful tool for testing the semiconductor laser beam's wavefront, especially the diffraction-limited wavefront.

A phase-shifting vectorial-shearing interferometer with wedge plate phase-shifter

We present a novel phase-shifting vectorial-shearing interferometer with a wedge plate phase-shifter. The interferometer is based on a modified Mach-Zehnder configuration; the common-path nature makes it capable of testing the wavefront of a short coherence-length light source, such as a laser diode. Vectorial shear (shearing in the x and y directions simultaneously) in an arbitrary direction is introduced by inserting two wedge plates orthogonally in two arms, respectively. One of the wedge plates is split into two parts (parallel part and wedge part); phase shift is produced by moving the wedge part in contact along the parallel part. The moving distance for a 2 pi phase shift is a few millimetres in specific conditions. The wedge plate phase-shifter increases the moving distance for phase shift and makes the control of phase shift relatively easy. We also discuss the lateral shear error and phase shift errors induced by wedge plates. The lateral shear error is small enough to be ignored; the phase shift error is determined mainly by the wedge angle error. Lastly, we give the experimental results of phase-shifting interference fringes in vectorial shear mode.

Parallel plate interferometer with a reflecting mirror for measuring angular displacement

A parallel plate interferometer with a reflecting mirror for measuring angular displacement is proposed. A deflection angle of a beam caused by an angular displacement is amplified by use of a reflecting mirror to increase the optical path difference (OPD) in the plane-parallel plate, which provides high sensitivity of the phase measurement. Detection of light transmitted through the plane-parallel plate with a position sensitive detector (PSD) enables high accurate measurement of the initial angle of incidence to the plane-parallel plate with insensitivity to stray light. The improved parallel plate interferometer achieves a measurement repeatability of 10(-8) rad. (C) 2007 The Optical Society of Japan.

Accuracy analysis of parallel plate interferometer for angular displacement measurement

The measurement accuracy of a parallel-plate interferometer for angular displacement measurement is analyzed. The measurement accuracy of angular displacement is not only related to the accuracy of phase extraction, but also related to initial incident angle, refraction index and thickness of plane-parallel plate as well as wavelength's stability of laser diode, etc. Theoretical analysis and computer simulation show that the measurement error of the angular displacement bears a minimum value when choosing an optimal initial incident angle in a large range. These analytical results serve as a guide in practical measurement. In this interferometer, reducing the refraction index or increasing the thickness of the parallel plate can improve the measurement accuracy; and the relative error of the phase measurement is 3.0 x 10(-4) corresponding to 1 degrees C temperature variation. Based on these theoretical and experimental results, the measurement accuracy of the parallel-plate interferometer is up to an order of 10(-8) rad. (c) 2007 Elsevier Ltd. All rights reserved.

Stabilization of optical Fabry-Perot sensor by active feedback control of diode laser

This paper presents the design and characterization of a fiber Fabry-Perot interferometer (FFPI) acoustic wave detector with its Q point being stabilized actively. The relationship between the reflectivity of the F-P cavity facets and cavity length was theoretically analyzed, and high visibility of 100% was realized by optimized design of the F-P cavity. To prevent the drifting of the Q point, a new stabilization method by actively feedback controlling of the diode laser is proposed and demonstrated, indicating the method is simple and easy operating. Measurement shows that good tracing of Q point was effectively realized. (c) 2008 Elsevier B.V. All rights reserved.

The convection during NaClO3 crystal growth observed by the phase shift interferometer

An optical diagnostic system consisting of the Mach-Zehnder interferometer with the phase shift device and an image processor has been developed for the study of the kinetics of the crystal growing process. The dissolution and crystallization process of NaClO3 crystal has been investigated. The concentration distributions around a growing and dissolving crystal have been obtained by using phase-shift of four-steps theory for the interpretation of the interferograms. The convection (a plume flow) has been visualized and analyzed in the process of the crystal growth. The experiment demonstrates that the buoyancy convection dominates the growth rate of the crystal growing face on the ground-based experiment.

The Real-Time Mach-Zehnder Interferometer Used In Space Experiment

The optical interference method is a promising technique for measuring temperature, density, and concentration in fluids. The non-intrusive and non-invasive nature of its optical techniques to the measured section are its most outstanding features. However, the adverse experiment environment, especially regarding shaking and vibrating, greatly restricts the application of the interferometer. In the present work, an optical diagnostic system consisting of a Mach-Zehnder interferometer (named after physicists Ludwig Mach) and an image processor has been developed that increases the measuring sensitivity compared to conventional experimental methods in fluid mechanics. An image processor has also been developed for obtaining quantitative results by using Fourier transformation. The present facility has been used in observing and measuring the mass transfer process of a water droplet in EAFP protein solution under microgravity condition provided by the satellite Shi Jian No. 8.

Near-diffraction-limited, 35.4 W laser-diode end-pumped Nd:YVO4 slab laser operating at 1342 nm

A diode stack end-pumped Nd:YVO4 slab laser at 1342 nm with near-diffraction-limited beam quality by using a hybrid resonator was presented. At a pump power of 139.5 W, laser power of 35.4 W was obtained with a conversion efficiency of 25.4% of the laser diode to laser output. The beam quality M-2 factors were measured to be 1.2 in the unstable direction and 1.3 in the stable direction at the output power of 29 W. (C) 2009 Optical Society of America