Self-Mixing Interference Effects in LD Pumped Multi-Mode Solid-State Laser

Based on the effective structure of the self-mixing interference effects,a general model for the self-mixing interference effects in the LD pumped solid-state laser has been established for the first time.The numerical simulation of the self-mixing interference signal has been done,the results show that when the external cavity length is integral times of 1/2,1/3,2/3,1/4,3/4 of the effective cavity length,the intensity of the self-mixing interference signals reach maximum in value.While that of single mode laser is integral times of half of the effective cavity length,the measuring precision of displacement of single mode laser is λ/2.A conclusion can be drawn from the above results that the measuring precision of displacement of multi-mode laser is higher than that of single mode laser.

Sub-external cavity effect and elimination method in laser self-mixing interference wave plate measurement system

Laser self-mixing interference（SMI） wave plate measurement method is a burgeoning technique for its simplicity and efficiency. But for the non-coated sample, the reflected light from the surface can seriously affect the measurement results.To analyze the reason theoretically, a self-consistent model for laser operation with a sub-external and an external cavity is established, and the sub-external cavity formed by the sample and a cavity mirror is proved to be the main error source.A synchronous tuning method is proposed to eliminate the sub-external cavity effect. Experiments are carried out on the synchronously tuning double external cavities self-mixing interference system, and the error of the system is in the range of -0.435°~0.387° compared with the ellipsometer. The research plays an important role in improving the performance and enlarging the application range of the laser self-mixing interference system.

Laser self-mixing interference fibre sensor

Fibre sensors exhibit a number of advantages over other sensors such as high sensitivity, electric insulation, corrosion resistance, interference rejection and so on. And laser self-mixing interference can accurately detect the phase difference of feedback light. In this paper, a novel laser self-mixing interference fibre sensor that combines the advantages of fibre sensors with those of laser self-mixing interference is presented. Experimental configurations are set up to study the relationship between laser power output and phase of laser feedback light when the fibre trembles or when the fibre is stretched or pressed. The theoretical analysis of pressure sensors based on laser self-mixing interference is indicated to accord with the experimental results.

An Optical Path Length Modulator for Laser Diode Self-Mixing Interference

Transparent liquid flattening or stretching realizes optical path length modulation. A flat thin seal transparent cavity, one flank is an electromagnetic driving membrane and is filled over with transparent liquid. Vibration of the membrane makes the liquid compressing or stretching, changes the liquid layer thickness, i.e. the optical path length of light through the liquid layer. The liquid layer compressed is equivalent to increase membrane tension. The membrane has higher resonant frequency. The cavity diameter 10 mm modulation frequency is about 18 kHz.

NEW SELF-MIXING MICRO-INTERFEROMETER BASED ON EXTERNAL PHASE MODULATION

ASeblsf-tmraicxti：n gA innteewrf esreelnf-cme ioxcincgu rms iicnr oa -liansteerrf derioodmee t（eLrD b）a sbeyd r eofnl eecxtitnergn tahl ep lhiagshet fmroomdu ala tmioinrr oisr-plirkees etanrtgedet. in front of the laser. Sinusoidal phase modulation of the beam is obtained by an electro-optic crystal （EOC） in the external cavity. The phase of the interference signal is demodulated by Fourier analysis method. The combination of the modulation and demodulation decreases the sensitivity of the instru-ment to fluctuations of the laser power and the noise induced by environment. Experimentally, the new micro-interferometer is applied to measure the micro-displacement of a high precision commer-cial PZT with an accuracy of 〈10 nm.

Displacement measurement method based on laser self-mixing interference in the presence of speckle

In order to achieve the accurate measurement of displacement, this Letter presents a self-mixing interference displacement measurement method suitable for the speckle effect. Because of the speckle effect, the amplitude of the self-mixing interference signal fluctuates greatly, which will affect the measurement accuracy of displacement. The ensemble empirical mode decomposition is used to process the interference signal, which can filter out high-frequency noise and low-frequency noise at the same time. The envelope of the self-mixing interference signal is extracted by Hilbert transform, and it is used to realize the normalization of the signal. Through a series of signal processing, the influence of speckle can be effectively reduced, and the self-mixing interference signal can be transformed into standard form. The displacement can be reconstructed by fringe counting and the interpolation method. The experimental results show that the method is successfully applied to the displacement measurement in the presence of speckle, which verifies the effectiveness and feasibility of the method.

Optical Measurements and Speckle Photography for Thermotropic Liquid Crystals Mixtures

In this work, an experimental approach of speckle photography was used for measuring birefringence of thermotropic liquid crystals mixtures at different wavelengths in the visible region. Also the dispersion relations were investigated. The values of the refractive indices were measured for these mixtures of thermotropic liquid crystals in isotropic and liquid crystal phase at different wavelengths. The effect of the end group of these LCs used on the values of birefringence was investigated and discussed.

电子剪切散斑3CCD传感图像特征去噪优化检测方法

针对CCD(Charge-Coupled Device)光学传感器采集电子剪切散斑干涉图像特征由于散斑指数高、峰值信噪比低,导致剪切散斑图质量差、检测效果不佳的问题,提出一种电子剪切散斑3CCD传感图像特征去噪优化检测方法。该方法分析了电子剪切散斑技术在三维物体表面变形检测中产生问题的原因,采用3CCD图像传感器替代单CCD图像传感器,引入同态滤波降噪处理图像,设计一种相位干涉技术,结合Canny检测算法,实现电子剪切散斑去噪优化检测。实验结果表明,应用3CCD传感器结合去噪技术的电子剪切散斑智能检测方法,图像散斑指数更低、峰值信噪比更高、检测时间更短,分别为0.0234、19.5 dB、16.2 ms,并且三维物体表面变形测量误差在0.09 mm内,该方法有效提高了图像质量,从而提高了实际应用价值。

Micro-Displace Sensor Based on Self-Mixing Interference of the Fiber Laser With Phase Modulation

Micro-displacement measurement based on self-mixing interference using a fiber laser system was demonstrated. The sinusoidal phase modulation technique was introduced into the fiber laser self-mixing interference measurement system to improve the measurement resolution. The phase could be demodulated by the Fourier analysis method. Error sources were evaluated in detail, and the system was experimentally applied to reconstruct the motion of a high-precision commercial piezoelectric ceramic transducer （PZT）. The displacement measurement resolution was well beyond a half-wavelength. It provides a practical solution for displacement measurement based on all optical-fiber sensing applications with high precision.

从恒星强度干涉仪、星体散斑干涉仪到空间强度自关联合成孔径望远镜

随着天文观测对空间分辨率性能需求不断提升,迫切需要发展十米级、百米级甚至公里级光学合成孔径的望远镜。传统光学共位相的合成孔径成像技术面临着高精度相位技术的挑战,难以将长基线的合成孔径成像拓展到光学波段。强度干涉的测量方法对相位相对不敏感,为长基线的光学合成孔径提供了可能的技术方案。分别梳理了恒星强度干涉仪、星体散斑干涉仪的发展历程和关键科学问题,并分析了空间强度自关联合成孔径望远镜的技术特点和发展潜力。通过总结三种技术方案的特点,可为我国发展长基线光学合成孔径成像系统提供参考。

改进的基于平稳小波变换的散斑去噪方法

针对剪切散斑干涉相位条纹图去噪过程中存在的噪声残留和边缘模糊问题,提出一种将正余弦分解和平稳小波变换相结合的散斑去噪方法,使用平稳小波变换对图像的正余弦分量进行小波分解,利用改进的小波阈值函数和阈值选取规则对分解后的高频图像进行处理,最后进行小波重构和反正切运算得到去噪后的相位条纹图。通过实验对各方法去噪后的效果进行分析,该方法能够保留边缘信息,改善相位图的质量,对比现有传统算法均方差分别降低了0.05、0.03,信噪比分别提高了3.1、1.1 dB。

离面位移的理论与实测值对比分析

以粗糙表面圆形物为对象,研究被测物体的离面位移。其基本路径是:推导出离面位移的理论表达式,暗条纹处离面位移等于半波长的整数倍。搭建实验光路,并通过ESPI专用软件进行调节,对试验成功的四个关键步骤进行详细说明。先通过干涉条纹前后变化数目计算出离面位移的理论值,再通过圆形变形物上的螺旋测微器测出离面位移的实验值。研究表明,实验值与理论值的相对误差仅为2.6%,吻合得非常好。

散斑干涉相位条纹图的频域滤波处理

为了解决在数字散斑干涉技术测量时,散斑干涉相位条纹图像中大量噪声对相位解包裹结果和精度产生严重影响的问题,介绍了一种条纹正余弦分解和频域低通滤波结合的方法,实现了散斑干涉相位条纹图的高精度滤波。该方法的基本思路是在对相位图像进行滤波处理前,先将相位图通过正余弦函数进行映射转换成两幅图,分别经过频域滤波,然后再合成为相位图。这种分解频域滤波方法可以在滤波的同时,有效保留相位跳变信息。实验结果表明：与传统的图像降噪方法相比,该方法能够在保留图像＂尖峰＂信息的基础上,较好地滤除图像中的散斑噪声,方法简单有效,有效解决了传统滤波方法应用在相位条纹图中,相图灰度信息丢失10%~40%的问题。

高速摄影激光照明技术取得新进展

采用衍射型光束匀化器件及多模光纤传光和透镜耦合扩束方法,有效抑制了激光散斑与干涉条纹,解决了大视场平行光束照明时拍摄物体在成像面上的渐晕问题,实现了300mm大口径视场下激光均匀照明和目标的清晰成像,并成功用于柱面内爆压缩、空间碎片等精密物理实验研究中。高速摄影技术与激光照明的成功结合,可有效抑制精密物理实验中强烈自发光导致过度曝光从而大大影响成像质量的问题,获得的物理过程边界形貌更加清晰,判读更精确。

基于条纹中心线法的电子散斑干涉条纹信息提取

电子散斑干涉技术(ESPI)是光学测量的一种重要的方法,对ESPI条纹的信息提取是ESPI进行光学测量的关键步骤之一,本文在介绍电子散斑干涉条纹中心线法的基础上,开展了ESPI条纹图预处理和基于条纹细化算法的骨架线提取的研究,包括对细化的条纹进行修整、拟合,该方法可以实现条纹骨架的快速、准确的自动提取。设计了一套应力形变装置,运用电子散斑干涉条纹中心线法对试件表面的形变进行实际检测,得到测量结果,对结果进行了分析,实验测量值与实际相符。

基于旋滤波的散斑干涉图预处理方法

介绍了旋滤波算法中窗口大小变化对滤波效果的影响,得出旋滤波的窗口应该取在约1/4条纹宽度的结论。处理了大散斑噪声的干涉图,发现窗口尺寸必须超过散斑尺寸才能得到比较好的滤波效果。确定了旋滤波算法应用的范围是大于散斑尺寸,且在1/4条纹宽度处比较合适。针对滤波后条纹对比度降低的问题,使用灰度拉伸的方法进行对比度增强。

基于FFT的散斑干涉术测物体变形

在SPI测量变形物体三维位相的原理上,提出了用一个干涉图法,基于二维FFT实现了散斑干涉图三维位相测试的新方法。选用马赫-泽德干涉系统,用CCD分别接收物体变形前后的散斑图,将两幅散斑图相减可以得到变形物体的散斑干涉条纹图。应用MAT LAB软件编程对散斑干涉图进行二维FFT运算,获得变形物体的三维位相。由三维位相分布可以判读物体的三维变形,进而为后续分析物体的三维应力奠定基础。实验表明,该方法简单、速度快,精度可达到λ/10。

相移测量技术中相移器研究

本文介绍一种用于相移测量技术的相移器。该相移器由计算机通过Ｄ／Ａ接口板自动控制输出电压幅度，其电路采用闭环控制，位移由压电晶体产生，具有很高的电压稳定度（０１％）和较小的相移误差（小于３°）。描述相移器的结构。

基于物体像的干涉条纹图像中散斑噪声的识别方法

散斑噪声是激光干涉时的普遍现象,其覆盖被测表面对应区域的形状信息,造成测量误差。针对斜入式激光干涉测量中散斑噪声的特点,提出一种基于物体像的散斑噪声的识别方法。该方法通过统计物体像中有效测量区域和背景区域内灰度分布的特点,自动计算出判定散斑噪声的上下阈值。基于物体像与干涉条纹图像间微米级的映射关系,得到干涉条纹图像中散斑噪声的位置。设计了相关实验,对干涉条纹图像中识别出的散斑噪声区域进行修补,消除了包裹相位图中一个条纹周期内相邻像素点间大于π的相位突变。

对集群光电成像传感器的多源协同相干激光干扰机理研究

目前激光干扰基本是一对一干扰模式,随着光电侦察传感器的大量使用,激光干扰急需面向集群目标的多对多干扰手段。立足于解决对集群化光电成像侦察的有效压制干扰问题,文中提出对集群光电成像传感器的多源协同相干激光干扰方法,以视场外散斑相干合成干扰作为多对多干扰实现的基本思路,探讨其相干干扰机理,建模分析双光束相干激光干扰光电传感器作用效果并提出对集群目标的协同干扰模型。仿真结果表明,激光入射角度是激光协同相干干扰的重要影响参数,能够作为干扰站协同部署的依据。同时,基于PSNR与MSE的图像质量评价结果表明,相干叠加干扰与单光束干扰以及非相干叠加干扰相比具有明显优势。