Sinusoidal Phase-Modulating Superluminescent Diode Interferometer with Fabry-Perot Etalone for Step-Profile Measurement

In this paper we use a superluminescent diode (SLD) as the light source of an interferometer and extract a narrow spectrum from a wide spectrum of the SLD with a Fabry-Perot Etalone (FPE). By varying sinusoidally the distance between the two mirrors of FPE, the central wavelength of the narrow spectrum is scanned sinusoidally. The distance between the mirrors is exactly set by a feedback control system, and sinusoidal phase-modulated SLD light that has a large scanning width of about 10 nm can be obtained with high stability and spatial uniformity. The phase of the interference signal has two different components. One is amplitude Z_b of sinusoidal phase modulation, which is proportional to the optical path difference (OPD) and the scanning width. The other is conventional phase α, which provides a fractional value of the OPD in the range of the wavelength. By combining the two values of the OPD obtained from Z_b and α, an exact OPD larger than the wavelength can be measure with ment accuracy in α. Characteristics of the interferometer are made clearly through step-profile measurements.     

Error-Compensating Phase Measuring Algorithms in a Fizeau Inter ferometer

In phase-shifting Fizeau interferometers, nonlinear motion of the phase shifter and multiple-beam interference are the most common sources of systematic errors affecting high-precision phase measurement. A new class of algorithms with extended compensating capability for these errors is proposed. Measurement errors for the new algorithms and two groups of conventional algorithms: discrete Fourier algorithms and the Schwider-Larkin-Hibino algorithms are estimated as a function of the number of sampled images when these systematic error sources are equally dominant. It is shown that the conventional phase-measuring algorithms produce significant errors when the reflectivity of the testing surface exceeds ten percent. Also, these algorithms have an optimum number of samples at around seven with which the residual errors become minimum. The new class of algorithms shows a substantial reduction of the residual errors when the number of samples exceeds ten. There is no optimum number of samples for the new algorithms. For fewer than six samples, discrete Fourier algorithms which have no error-compensating capability for the nonlinearity of phase modulation give a minimum error.     

Heterodyne Interferometers Using Orthogonally Polarized and Two-Frequency Shifted Light Sources with Super-high Extinction Ratio

This paper describes heterodyne interferometers using orthogonally polarized and two-frequency shifted light sources of two types with super-high extinction ratio to reduce non-linearity of the interferometer due to polarization cross-talk. The acousto-optic modulators are used to shift light frequency. In the first interferometer the light source with Glan-Thomson prisms of very high extinction ratio (50 dB) is used to make the polarization cross-talk very small. In the second interferometer the light source of two-frequency shifted beams with small crossing angle (2.5 rnrad-10 mrad) is used to completely exclude non-linearity of the interferometer due to polarization cross-talk. By measuring the thickness of vacuum evaporation film, it was demonstrated that the interferometers are useful to measure thickness of a thin film in nanometer order.     

High-sensitivity laser-based ultrasonic C-scan system for materials inspection

A beam-steering C-scan system for laser generation and detection of ultrasound in opaque solids has been developed. For ultrasound detection, the system uses a confocal Fabry-Perot interferometer that is stabilized at its high-sensitivity point by implementing a novel procedure that does not require a reference beam. This stabilization procedure effectively compensates for slowly varying (up to 2 Hz) disturbances and, more important, for any change in the interferometer illumination conditions while probing different scanning points. For the latter reason, the proposed stabilization appears to be more effective than previous approaches for high-sensitivity ultrasound detection in beamsteering scans. Noise performance and sensitivity limit of the system are evaluated. Ultrasonic echoes are detected in aluminum samples having optically rough surfaces with single-pulse generation signal-to-noise ratios on the order of 20 dB. A C-scan inspection is performed where a known defect in the test piece is successfully detected by time-of-flight gating of the ultrasonic signals.     

光学层析技术在中央处理单元散热中的应用研究

将光学层析技术实际应用于中央处理单元（ＣＰＵ）散热产生的温度场的重建中,指出了由多方面干涉投影重建三维场的实际应用意义。成功地解决了稳态场和似稳态场的我步步投影的获取问题。     

光学相干层析成像的实验研究

用光纤迈克耳孙干涉仪方法,建立了一种相干门层析成像实验装置,在此系统中,采用相干长度仅为２５ｕｍ的超辐射管作光源,测量了样品浸泡在牛奶乳浊液情况下的干涉信号。     

光纤干涉测距中光程定位的研究

提出一种由定位干涉仪和测量干涉仪组成的光纤干涉绝对距离测量方法;并用标准长度光纤实现光程倍增以增大测量范围;重点讨论了用脉冲电流调制的准单色光源实现光程定位的方法及其精度。通过理论分析和仿真实验,定位重复性误差优于±1μm。     

严谨而精密的创新——瑞利进行研究的特点

着重介绍了瑞利在测量氮气密度过程中发现惰性气体氩的研究和创新历程,以及瑞利对光学、声学等物理学的各个领域的主要贡献,指出正是求实的科学态度、锲而不舍的钻研精神和以创新为乐趣的事业追求是瑞利一生中取得丰硕的研究成果的主要原因。     

Phase-difference amplification using a Sagnac interferometer

In this paper, we describe a new method for achieving phase-difference amplification, which is quick and convenient, operates in real time, and requires no photographic steps. Magnification factors of 2, 4 or 6 are achieved easily in one step. Because the system operates in real time, phase stepping may be applied to extract the amplified phase distributions. Our method is a variation on longitudinally reversed shearing interferometry, using first- or higher-order diffraction from a grating (hologram) which is in fact the interferogram of the wavefront under test. The grating is derived from a standard two-beam interferometer which is phase-stepped, and displayed in real time on a spatial light modulator in the phase-difference amplification setup. It is illuminated by the two output beams from a Sagnac interferometer, similar to the set up used by (Barnes et al. Barnes TH, Eiju T, Matsuda K. Appl Opt 1986; 25:1864). for spectral resolution enhancement, and a phase-amplified fringe pattern is obtained by spatial filtering using a Fourier transform lens. We demonstrate operation of the phase amplifier and show amplified phase maps retrieved by phase-stepping. We believe this is the first time that real-time phase amplification without photographic steps and with phase stepping has been demonstrated.     

Analysis of nonlinearity in a high-resolution grating interferometer

Metrological feasibilities of a high-resolution grating interferometer (GI) based on a transverse Zeeman laser are investigated. When the grating pitch equals 20 μm, a resolution of 0.7 nm is obtained by means of a heterodyne signal processing method. The comparison of two approaches for determining the residual nonlinearity is presented. One is to evaluate the maximum residual error by determining the amplitude modulation degree of the measurement signal. The other is to do a high precision calibration with a differential dual-frequency interferometer that has a higher precision. The experimental results show that the nonlinearity is no more than 25 nm which fits well with the estimating result. Analysis of the depolarization effect of the grating indicates that it has little influence on the measurement accuracy.