移相干涉仪环境微扰的外差检测及信号处理

对环境微振动干扰进行补偿可减小移相干涉测量的误差,其中振动量的检测是实现振动补偿的前提。以声光调制器作为光学移频器,在移相式平面干涉仪中组合成外差干涉测振系统,可以实现光程差微小变化(范围为0到1/2波长)的实时检测。在外差信号处理中采用单片RF/IF相位测量芯片直接对两路40MHz模拟信号进行比相,简化了通常使用的数字测相方法,其精确测相的典型非线性值小于1度。用该系统实际测量了周期性振动和地面冲击振动对干涉仪的影响,获得了干涉仪所受微振动的幅度和相位。     

Heterodyne grating interferometer based on a quasi-common-optical-path configuration for a two-degrees-of-freedom straightness measurement

We present a heterodyne grating interferometer based on a quasi-common-optical-path (QCOP) design for a two-degrees-of-freedom (DOF) straightness measurement. Two half-wave plates are utilized to rotate the polarizations of two orthogonally polarized beams. The grating movement can be calculated by measuring the phase difference variation in each axis. The experimental results demonstrate that our method has the ability to measure two-DOF straightness and still maintain high system stability. The proposed and demonstrated method, which relies on heterodyne interferometric phase measurement combined with the QCOP configuration, has the advantages of high measurement resolution, relatively straightforward operation, and high system stability.     

Analytical modeling of the periodic nonlinearity in heterodyne interferometry

The periodic nonlinearity that arises from nonideal laser sources and imperfections of optical components limits the accuracy of displacement measurements in heterodyne interferometry at the nanometer level. An analytical approach to investigating the nonlinearity is presented. Frequency mixing, polarization mixing, polarization-frequency mixing, and ghost reflections are all included in this investigation. A general form for the measurement signal, including that of the distortions, is given. The analytical approach is also applicable to homodyne interferometry.     

Enhancement of optical nonlinearity in periodic gold nanoparticle arrays

Linear and nonlinear optical properties of periodic triangular Au nanoparticle arrays were investigated. We compared the optical nonlinearity of periodic Au nanoparticle arrays with that of the ultra-thin gold film consisting of randomly distributed spheroidal clusters. A pronounced enhancement of the third-order nonlinear optical susceptibility χ((3)) in Au arrays was observed, and the figure of merit, χ((3))/α, of the periodic nanoparticle arrays is one order of magnitude larger than that of the ultra-thin film. Such an enhancement of the optical nonlinearity could be due to the strong local field near the triangular nanoparticles.     

Conversion-characteristic nonlinearity for periodic pulsed laser radiation acting on microwire bolometers

Expressions are derived for the normalized conversion coefficients for a thin- wire bolometer acted on by high-intensity periodic laser pulses, which relate the resistance change and the area under the cooling curve to the energy incident per unit length, the pulse repetition frequency, and the nonuniformity in the energy distribution along the bolometer. Results are given for a platinum bolometer and a wavelength of 10.6 m. A method is given for eliminating the systematic error due to the conversion nonlinearity.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 30–32, September, 1993.     

Removing nonlinearity of a homodyne interferometer by adjusting the gains of its quadrature detector systems

Most homodyne interferometers have a quadrature detector system that includes two polarizing beam splitters that cause nonlinearity of the order of a few nanometers by phase mixing. Detectors should have the same gains to reduce nonlinearity under the assumption that there is no loss in optical components. However, optical components exhibit some loss. We show that nonlinearity can be reduced to an order of 0.01 nm when the detector gains are adjusted by simulation to include the optical characteristics. The compensated nonlinearity is 18 times smaller than that when the four detector gains are set to be equal.     

Heterodyne Interferometer with Photorefractive BGO Crystals

Abstract

In this paper we show that it is possible to make a heterodyne interferometer with a single photorefractive BGO crystal using the technique of moving gratings. The main problems of obtaining good fidelity of the phase conjugate wavefront with such a method are discussed theoretically within the framework of the well-known scalar approximation to the photorefractive four-wave mixing process (no absorption, no pump depletion). Experimental phase measurements for obtaining the phase distribution of the signal wave are also presented.     

Heterodyne vibration measurement

Analytic expressions are derived for the vibration amplitude and frequency in a heterodyne measurement method. The measurement accuracy is estimated.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 39–40, August, 1993.     

Heterodyne detection with a weak local oscillator

Heterodyne detection in the limit of weak (a few photons) local oscillator and signal power levels has been largely neglected in the past, as authors almost always assumed that the noise was dominated by the shot noise from a strong local oscillator. We present the theory for heterodyne detection of diffuse and specular targets at arbitrary power levels, including the case where the local oscillator power is only a few photons per coherent integration period. The theory was tested with experimental results, and was found to show good agreement. We show how to interpret the power spectral density of the heterodyne signal and how to determine the optimal number of signal and local oscillator photons per coherent integration.     

Two-spherical-wave ultraviolet interferometer for making an antireflective subwavelength periodic pattern on a curved surface

An ultraviolet two-spherical-wave interferometer was developed in order to make a subwavelength structured surface on a curved surface. The change in fringe period on the curved surface was significantly suppressed compared with the two-plane-wave interferometer. The optical setup method for suppressing the change in fringe period is described. The effect of the two-spherical-wave interferometer was investigated by numerical simulations. In an experimental demonstration for a concave spherical surface with 11.1 mm radius of curvature and 10 mm diameter, the change in period of the photoresist pattern was reduced to 12 nm for the target period of 250 nm.     

Coherent Infrared Lidar with Enhanced Optical Heterodyne Detection

Abstract

Enhanced operation of a coherent infrared differential absorption lidar was demonstrated in case when appropriately selected laser sources were used. Good agreement with experimental data supports the idea that, in the case of reinjecting the weak frequency shifted signal into the source laser cavity (autodyne arrangement), a model based on forced relaxation oscillations can describe the operation of the system.     

Heterodyne temporal speckle-pattern interferometry

In temporal speckle-pattern interferometry deformation information is extracted by a Fourier transform technique from the speckle pattern that is recorded over a period of time as the object is deformed. A limitation of the experimental arrangements reported to date is that the direction of the deformation cannot be determined. We propose removing this limitation by using the heterodyne principle. Some experimental results that were obtained by use of a rotating half-wave-plate frequency shifter are presented.     

Filtration law with quadratic nonlinearity

A quadratic filtration law which generalizes the Darcy and Brinkman laws is considered.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 5, pp. 753–757, November, 1986.     

非接触型光外差轮廓仪

本文介绍一种纳米级非接触型高精度光外差轮廓仪,它是基于普通光路的光外差干涉仪。工件表面被两束有微小频差的激光束所照射,其中一束经聚焦后用作测量光探针来扫描工件表面,另一束则用作参考光束。两束光经表面反射后产生干涉。测量信号和参考信号的相位差与表面的微不平值成正比。仪器的横向分辨率为2μm,高度分辨率为1 nm,它不需要对试样作大范围的调整,且可用试样自身作参考面。信号经光电转换后由微型计算机进行处理,它能快速完成测量、计算、显示及打印出各种参数和曲线。