移相干涉测量术及其应用

为了对移相式数字干涉仪在光学元件测量中的应用有全面了解，介绍了移相干涉术的基本原理。结合激光数字波面干涉仪，阐述移相干涉术的四步重叠平均算法、压电晶体移相器(PZT)的结构、3 PZT的组合方法、移相器的标定误差和非线性误差的校正方法、波面相位解包的自适应种子算法、波面相位的评价指标等内容。结合移相数字波面干涉仪，叙述了移相干涉测量技术在普通光学元件、红外光学元件、大口径光学元件、非球面光学元件等测量中的应用并指出了应用过程中的注意事项。最后明确指出光干涉技术正沿着高相位分辨率、高空间分辨率、宽波段和瞬态高速测量的方向发展，并将会在瞬态波前测量、微机械的微结构动态分析等方面有着越来越广泛的应用。     

Spatial-carrier phase-shifting digital holography utilizing spatial frequency analysis for the correction of the phase-shift error

We propose a single-shot digital holography in which the complex amplitude distribution is obtained by spatial-carrier phase-shifting (SCPS) interferometry and the correction of the inherent phase-shift error occurred in this interferometry. The 0th order diffraction wave and the conjugate image are removed by phase-shifting interferometry and Fourier transform technique, respectively. The inherent error is corrected in the spatial frequency domain. The proposed technique does not require an iteration process to remove the unwanted images and has an advantage in the field of view in comparison to a conventional SCPS technique.     

Fast localized wavefront correction using area-mapped phase-shift interferometry

We propose an innovative method for localized wavefront correction based on area-mapped phase-shift (AMPS) interferometry. In this Letter, we present the theory and then experimentally compare it with a previously demonstrated method based on spot-optimized phase-stepping (SOPS) interferometry. We found that AMPS outperforms SOPS interferometry in terms of speed by threefold, although in noisy environments the improvements may be larger. AMPS yielded similar point-spread functions (PSF) as SOPS for moderate system-induced aberrations, but yielded a slightly less ideal PSF for larger aberrations. The method described in this Letter may prove crucial for applications where the phase-stepping solution does not have sufficient speed.     

An effective method in calibrating nonlinear errors for phase-shifting interferometry

In phase measurement or digital holography for phase-shifting interferometry, the key role is the variation of reference light wave and recover algorithm based on interferograms and reference phase, so the calculation result is directly affected by phase-shift accuracy. However, because of the errors of nonlinear and other random factors, it is difficult to control the actual phase-shifting amount accurately. In this paper, we aim to propose an efficient method for phase-shifting interferometry which does not require accurate initial estimation of phase-shift amounts, only a few pixels with several randomly shifted interferograms are sufficient for accurate extraction of phase information. This method has reduced the dependence of reference phase, and can obtain phase-shifting amount directly without using complex revised algorithm for correcting phase-shifting nonlinear errors.     

Analysis by speckle interferometry of the dependency of yield stress on residual stress

We used electronic speckle pattern interferometry (ESPI) to measure in situ displacement fields nondestructively and with high resolution (10⁻² μm) by using the interferometry principle and the phase-shift technique. We measured the depth profile of the residual stress in steel pipe manufactured by thermomechanically controlled processing using a quantitative model, which explains the relationship between residual stress and displacement measured by ESPI in chemical etching. We analyzed the variation of yield stresses measured by the indentation technique and the residual stresses at various depths. The relationship between the residual stresses and the yield stresses was consistent with simulated results and can be used for indirect evaluation of the residual stresses from the yield stresses.     

大口径光学平面的子孔径拼接检验研究

研究了检测大口径光学平面的子孔径拼接法。通过采用最小二乘法对相邻两个子孔径重叠区域的数据进行分析,获得了子孔径之间的拼接参量,得到了被检验镜面的整体面形信息。编制了拼接检验的计算程序,并完成了原理性实验。采用一台口径为100mm的移相干涉仪检测了两个样品,给出了拼接检测与全口径检测的对比结果。样品的口径分别为100mm和91mm。对比检测结果表明,拼接检测与直接检测两种方法的RMS之差小于5nm。     

应用移相干涉术测量量块长度和长度变动量

研究了应用移相干涉术测量新的一等量块的方法。对于干涉图像进行多幅图的采样，由移相法计算量块测量面和与其研全的辅助平晶表面的波面面形，着重研究了在量块干涉图中有阶跃不连续的波面复原运算的原理与技术，得到一幅表征它们表面的离散滤差值，并给出量块工作面长度和长度变动量的测量结果。     

Phase-shift interferometry combined with surface plasmon resonance effect for two-dimensional bio-surface analysis

The phase-shift interferometry combined with surface plasmon resonance (SPR) effect has been studied as a novel technique used to analyze the bio-surface, which measures the spatial phase variation of SPR reflected light. The spatial sensitivity of the SPR imaging sensor is improved over the conventional SPR imaging systems based on optical intensity.     

Generalized method for wave-front analysis

We suggest and demonstrate a new method for wave-front analysis based on common-path phase-shift interferometry. We introduce a formalism and an iterative mathematical algorithm in which the wave front is transformed, modified, and inversely transformed. The resulting intensity data are sufficient to reconstruct the entire wave front. In a more restricted case, in which the wave-front modifications are arbitrarily applied over arbitrary spatial regions of the wave front, the wave front is reconstructed semianalytically by use of a model that allows a local solution, followed by an iterative algorithm. Measurement results indicating that the suggested approach has an improved measurement accuracy with respect to existing quantitative phase measurement methods are presented.     

线性啁啾脉冲频域-时域相移转换的模拟研究

在超快激光与物质相互作用的实验中, 实现单束实时的频谱干涉测量对提高测量精度很重要。基于频谱干涉原理和线性啁啾脉冲瞬时频率与时间的线性关系对啁啾脉冲频域相移直接映射为瞬态时域相移的原理进行了理论研究; 推导出这种频域-时域相移映射模式成立的限制条件。对相移直接映射过程进行了数值模拟和分析, 结果显示, 该方法可以得到具有瞬态特性的时域相移, 具有单束测量的能力; 在微扰和带宽一定的条件下, 增加探测脉冲的啁啾量, 可以减小频域-时域相移映射过程中产生的误差。     

He-Ne laser wavelength-shifting interferometry

The use of wavelength-shifting interferometry with a He-Ne laser source is presented. The approach is based on the thermal expansion of the laser cavity during the warm-up time, in conjunction with an unequal path interferometric configuration. The optics principles are reviewed, and a demonstrative measurement is presented. The technique extends the capability of phase-shift acquisition and processing to cases where conventional methods with piezoelectric transducers cannot be used, and particularly to external measurement cavities of large diameter.     

基于剪切散斑干涉技术的物体变形动态检测

为使仅适用于静态测量的空间相移剪切散斑干涉系统可用于物体变形的动态测量,在对传统剪切散斑干涉系统加以改进的基础上,提出一种物体变形动态检测方法。将检测系统中的压电陶瓷控制器用参考镜代替,减少了物理装置控制与执行的时间。对于物体发生变形的同一状态,仅需采集一幅干涉图像即可满足后期计算,加以二维连续小波滤波和最小二乘相位解包算法,能满足物体变形动态在线检测的需求。理论和实测实验表明,该方法能快速可靠地检测出物体动态形变,整个系统的最大误差范围在-1.5 rad~1.5 rad之间,整个检测过程最大误差百分比为6.4%,有较高的精度和实用性,为新型剪切散斑干涉测量系统的改进和设计提供参考。     

Photo-induced densification in Er<Superscript>3+</Superscript>/Al doped silica preform plates using 193-nm laser light

The growth rate of Bragg gratings written using 193-nm light from an ArF excimer laser is shown to be non-linear with the pulse energy density for Er³⁺ co-doped Al silica. This yields a refractive-index increase up to a few 10⁻³. We then use phase-shift interferometry to measure the sample surface topography following exposure. Subsequently, we formulate an inhomogeneous stress model to analyse the observed change of volume within the core material. Below pulse energies of 550 mJ/cm², the results show that refractive-index changes are primarily due to a densification process. At higher pulse energies material re-expansion occurs.     

Simultaneous measurement of several near-parallel surfaces with wavelength-shifting interferometry and a tunable phase-shifting method

Wavelength-shifting interferometry can distinguish in frequency space interference signals from different surfaces, and therefore allows the measurement of optical thickness variation between several quasi-parallel surfaces of a composite transparent object. Frequency analysis of the signal spectrum with a tunable phase-shifting formula can then detect the phase of the individual signals. We have devised a tunable phase-shifting method which uses a freely adjustable number of intensity samples and can be adapted to any frequency spectrum. To extract the signal reliably, two properties of the phase-shifting method are particularly important: it should suppress cross-talk from unwanted frequencies, and it should allow for some variation in the signal frequency. We show that a carefully designed sampling function envelope will combine these benefits, and demonstrate the technique in measurements of three different composite objects each consisting of three reflecting surfaces. The importance of phase-shift linearisation is discussed, and methods for selecting optimal set-up parameters are given.     

Visualization of 50 MHz Surface Acoustic Wave Propagation Using Stroboscopic Phase-Shift Interferometry

A Stroboscopic phase-shift interferometry has been developed to visualize surface acoustic wave (SAW) propagation on SAW devices quantitatively. The developed interferometry is a Fizeau-type one with a multi-mode semiconductor laser diode and an optical isolator. With the laser light illuminating stroboscopically, observed interference intensity gives information about average displacements of the vibrations. Fifty MHz SAW propagation on the surface of the SAW device has been measured with the interferometry. Distribution of the SAW along the propagation path has been observed, whose amplitude is 3 nm (p-p). Repetition accuracy evaluated with the root mean square method is 1/2500 of the laser wavelength. The system is useful for estimating and improving performances of micro-devices.Presented at 1996 International Workshop on Interferometry (IWI ‘96), August 27-29, Saitama, Japan.     

Single-element interferometer

A very simple and stable interferometer using a single optical element - a beam-splitter cube - is presented. The device resembles a two-arm interferometer in which the arms are together in one collimated beam, and the two beam halves interfere with the help of the beam-splitter cube. The proposed device produces simultaneously two interferograms with a relative phase-shift of π (rad). Since the period of straight interference fringes can be stably controlled, the device has potential application in spatial-carrier interferometry and for flexible writing of fiber Bragg gratings.     

Removal of residual images in parallel phase-shifting digital holography

Parallel phase-shifting digital holography (PPSDH) is a technique of single-shot phase-shifting digital holography. We found that there are two problems with this technique. (1) Some extraneous noises caused by the intensity unevenness of the reference wave become slightly superimposed on the object image. (2) The conjugate image cannot be completely removed. This is because the object wave causes the phase-shift error by illuminating an image sensor with a large incident angle. To solve these problems, we propose an algorithm for removing residual 0th-order diffraction and conjugate images in PPSDH. In the proposed algorithm, we modified phase-shifting interferometry in order to work through the unevenness of the intensity distribution and applied the Fourier transform technique to PPSDH to remove the residual conjugate image. The effectiveness of the proposed algorithm was experimentally verified.     

剪切电子散斑平移棱镜相移方法研究

在剪切电子散斑干涉中,由于错位的二物光束同向传播,很难将二物光分开引入附加相位的方法来实现相移.平移棱镜相移法可以在二束物光不分开的情况下实现相移.本文对平移棱镜相移法进行了理论分析,证明平移棱镜可以引入稳定、线性的附加相位,给出了附加位移与附加相位之间的关系式.利用周边固定、中心加载的圆盘进行实验,给出了实验结果,证明平移棱镜相移法可以有效地从干涉条纹中定量提取位移导数信息.     

一种提高干涉相位识别精度的方法

针对开环相移驱动下的单色光干涉测量,提出一种满足四步法的高精度相位识别的方法。首先选取干涉场中存在适当相位差的两像素点,建立相移驱动单周期内两像素点灰度序列值之间的干涉方程组。运用椭圆拟合获取相应干涉方程组参数,然后通过反算序列相位确定逐点驱动步长或序列相位信息。结合序列相位信息,运用Lagrange抛物插值算法,设计计算满足四步法的4幅干涉图,并计算各像素点的初相位。最后,运用多波长算法计算表面形貌并进行误差分析。实验表明:计算得到的方波多刻线样板的Ra值为0.439 0 m,测量误差为0.23%,此方法降低了对测量条件的硬件与环境要求,满足表面形貌高精度测量的要求。     

Generalized phase-shifting interferometry with arbitrary unknown phase steps for diffraction objects

A general method of extracting the arbitrary unknown and unequal phase steps in phase-shift interferometry from interferograms recorded on the diffraction field of an object and then reconstructing the object wave front digitally with our derived formulas is proposed. The phase steps are first calculated based on the statistical nature of the diffraction field and are further improved by an iterative approach. This method is simple, highly accurate, and usable for any frame number N (N > or = 3) and for both smooth and diffusing objects, as is verified by a series of computer simulations.