Electro-optic heterodyne interferometer

We propose a new configuration for using a triangle-wave signal to drive the electro-optic modulator in an electro-optic heterodyne interferometer system. The new configuration is adapted to measure the phase retardation of a wave plate and the optical rotation angle of a chiral medium. By adding optic elements, the second-harmonic component amplitude of the interferometer photodetector output signal became proportional to the phase retardation or optical rotation angle of the samples being tested.     

Jones matrix analysis of frequency mixing error in three-longitudinal-mode laser heterodyne interferometer

In this study, the authors investigate theoretically a periodic non-linearity effect and its compensation in a three-longitudinal-mode heterodyne interferometer (TLMI). An analytical formula of the frequency mixing error in the TLMI is obtained based on the Jones calculus taking into account experimental parameters. We find that the non-ideal polarisation states and imperfect alignment of the optical setup play the major role to produce four- and eight-cycle non-linearities. The operation of non-linearity compensation system on the four- and eight-cycle non-linear errors is also presented.     

An analysis of the polarization component of the measurement error in heterodyne laser interferometer measurement systems

The reasons for the occurrence of the polarization component of the measurement error in heterodyne laser interferometer measuring systems are considered. An analysis of this component is given.     

Automatic alignment of a displacement-measuring heterodyne interferometer

A technique to align automatically the beams of displacement-measuring interferometric gauges is described. The pointing of the launched beam is modulated in a circular pattern, and the resulting displacement signal is demodulated synchronously to determine the alignment error. This error signal is used in a control system that maintains the alignment for maximum path between a pair of fiducial hollow-cube corner retroreflectors, which minimizes sensitivity to alignment drift. The technique is tested on a developmental gauge of the type intended for the Space Interferometry Mission. The displacement signal for the gauge is generated in digital form; and the lock-in amplifier functions of modulation, demodulation, and filtering are all implemented digitally.     

A heterodyne laser interferometer for dilatometer measurements

A dilatometer measuring system based on heterodyne laser interferometry is described. An electrooptical light modulator based on the double transverse Pockels electrooptical effect in a crystal of lithium niobate and operating in the quarter-wave mode is used as the optical heterodyne. The electronic measuring system uses modern microelectronic components with a high degree of integration.     

A heterodyne laser interferometer with digital phase conversion

The structure and metrological properties have been determined for processing with digital logic applicable to a wide range of heterodyne laser interference systems employing digital phase monitoring in the submicrometer and nanometer resolving power ranges. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 13–18, June, 2006.     

Two-wavelength heterodyne interferometer with an expanded measurement range

Translated from Izmeritel'naya Tekhnika, No. 8, pp. 39–40, August, 1992.     

Differential phase decoder in a polarized optical heterodyne interferometer

A differential-phase decoder (DPD) together with a polarization common-path optical heterodyne interferometer is set up. Based on this interferometric configuration and a novel balanced-detector scheme, the performance of the quantum-noise-limited differential-phase decoder is demonstrated and analyzed. The minimum-detectable differential phase is on the order of 10(-7) rad/sqrt Hz when a 2.5 mW He-Ne laser is used. Verified experimentally, the DPD is immune to the common-phase noise induced by an electro-optic phase modulator or by thermal disturbance within the interferometer. This signifies that the minimum-detectable differential phase can become 10(-8) rad/sqrt Hz if a 300 mW continuous wave laser is employed instead.     

Estimating phase errors in heterodyne laser interferometer measurement systems

An approach is described for estimating the phase error owing to frequency fluctuations of the laser radiation in laser heterodyne interference measurement systems.     

Differential wavelength-scanning heterodyne interferometer for measuring large step height

An interferometer based on the differential heterodyne configuration and wavelength-scanning interferometry for measuring large step heights is presented. The proposed interferometer is less sensitive to environmental disturbances than other interferometers and can accurately measure interference phases. A tunable diode laser is utilized to illuminate the interferometer and thus solve the phase ambiguity problem. Counting the interference fringes as the wavelength is scanned through a known change in wavelength directly determines the step height. Three gauge blocks of different lengths, 5, 10, and 50 mm, are individually wrung on a steel plate to simulate large step heights. Comparing the results measured by the proposed interferometer with those by the gauge block interferometer reveals that the accuracy is approximately 100 nm.     

Phase-shifting interferometer based on changing the direction of linear polarization orthogonally

We present a new type of phase-shifting interferometer, which utilizes a polarizing prism to form quadrature phase-shifted fringe patterns onto a single imaging sensor. By changing the direction of linear polarization of the incident light orthogonally, four phase-shifted fringe patterns in quadrature are obtained by taking images twice; thus it is possible to reduce phase errors caused by mechanical vibrations and air turbulence that occur in temporal phase-shifting interferometers. We present the principle of this interferometer with its theoretical analysis, using the Jones matrix, along with experimental results.     

An electro-optic modulated heterodyne interferometer for measuring low glucose concentration

An electro-optic modulated heterodyne interferometer using the phase-lock technique for measuring the optical rotation angle corresponding to glucose concentration is presented. By inserting a half-wave plate behind the test sample and using the heterodyne interferometric phase-lock technique, it demonstrates a high sensitivity and is capable of measuring low glucose concentration. The validity of the proposed design is demonstrated by the measurements of rotation angles in a half-wave plate sample and the glucose sample, respectively. A correlation coefficient value of 0.999993 indicates a high linear response between the reference rotation angle and the measured rotation angle in a half-wave plate. Moreover, a standard deviation in rotation angle level of 5.9^○ × 10^?4 has been obtained for glucose solutions with concentrations ranging from 0 to 1.2 g dl^?1, with a correlation coefficient value of 0.99989 between the measured rotation angle and the glucose concentration. A standard deviation of rotation angle around 1.5^○ × 10^?4 is achieved according to the repeatability experiments, and the relative error of rotation angle corresponding to the lowest measurable concentration of 0.01 g dl^?1 has been determined to be 5.88%.     

Angstrom-range optical path-length measurement with a high-speed scanning heterodyne optical interferometer

A highly accurate method of optical path-length measurement is introduced by use of a scanning heterodyne optical interferometer with no moving parts. The instrument has demonstrated the potential to measure optical path length at angstrom resolution over continuous thickness in the micrometer range. This optical path length can be used to calculate the thickness of any material if the refractive index is known or to measure the refractive index of the material if the thickness is known. The instrument uses a single acousto-optic device in an in-line ultra-stable reflective geometry to implement rapid scanning in the microsecond domain for thickness measurements of the test medium.     

偏振分光镜传输系数不等对非线性误差的影响

为了减小激光外差干涉非线性误差,必须考虑偏振分光镜透过率和反射率不等对非线性误差的影响。通过分析两臂透过率与反射率不等对测量信号的影响,推导出两臂反射率与透过率不等对激光外差干涉非线性误差一次谐波和二次谐波影响的理论模型。仿真结果表明,透过率与反射率不等将严重的影响非线性误差一次谐波的大小,当反射率为1而透射率由1变为0．85时,其非线性误差由0、56nm增加到2．03nm,同时非线性误差只是一次谐波和二次谐波的简单叠加。仿真结果表明调整偏振分光镜的旋转角度误差能够有效的消除两臂透过率与反射率不等对非线性误差的影响。为进一步指导调整减小或消除非线性误差提供了理论依据。     

Optical activity measurement by use of a balanced detector optical heterodyne interferometer

What we believe to be a novel amplitude sensitive optical heterodyne polarimeter in which a Zeeman laser is associated with balanced detector detection was set up. The aim was to measure the optical activity of a quartz crystal with a Cornu depolarizer at high accuracy. The features of this novel polarimeter, which include the use of a two-frequency laser that ensures the accuracy of the measurement, are discussed. Furthermore, the detection sensitivity of the optical activity of a quartz crystal was measured as 8.5x10(-10). To our knowledge, this is the highest sensitivity obtained for optical activity measurement of a quartz crystal when the error of the measurement is also analyzed.     

Stabilization improvements of laser-diode closed-loop heterodyne phase-shifting interferometer for surface profile measurement

To stabilize the phase-shifting Fizeau-type interferometer against environmental disturbances (namely, vibration and temperature variations), the feedback scheme that uses the current-induced frequency modulation of a laser diode (lambda = 633 nm) and the two-frequency optical heterodyne method has been investigated, with particular attention to improvement of the achievable stabilization. It is demonstrated that introduction of the proportional-integral control into the feedback system improves stabilization against the proportional control case; e.g., stabilization is improved 5 times for 100-nm(p-p) vibration at the frequency range at 30 Hz. The surface profile measurement for a sample mirror was conducted with a reproducibility of 6.8 nm in the root mean square under the subwavelength-amplitude vibration at 100 Hz.     

Quasi-optical diplexer and filter based on a polarization ring interferometer

The operation of a quasi-optical polarization ring interferometer (PRI) performing the function of a diplexer, bandpass filter, and band-stop filter is demonstrated for the first time. It is shown that the beam focusing losses in this interferometer can be reduced using spherical low-permittivity lenses. The results of measurements of the transmission characteristics of a PRI prototype in a 3-mm wavelength range are presented.