PGC demodulation real-time normalization correction device and method in sinusoidal phase modulation interferometer

Abstract

The invention discloses a PGC demodulation real-time normalization correction device and method in a sinusoidal phase modulation interferometer. An optical path structure containing a measurement interferometer and a monitoring interferometer is constructed, an electro-optic phase modulator is placed in a public reference arm of the two interferometers, and high-frequency sine wave modulation andlow-frequency triangular wave modulation are applied at the same time; sinusoidal modulation is used to generate phase carriers, and PGC demodulation is carried out to obtain orthogonal signals containing to-be-measured phase information; the triangular wave modulation enables the orthogonal signals to change periodically, a Lissajous figure corresponding to the orthogonal signals is subjected toellipse fitting, and real-time normalization correction on the PGC demodulation orthogonal signals is realized; and measured displacement is calculated through calculating the phase difference variation between the two paths of interference signals, and nanoscale displacement measurement is realized. Nonlinear errors caused by changes of a phase modulation depth, phase delay, multiplier and filtergains and the like in PGC demodulation are eliminated, sub-nanometer measurement precision can be achieved, and the device and the method disclosed in the invention are applicable to precision displacement measurement in the high-end equipment manufacturing and processing field.

Description

technical field [0001] The invention belongs to the technical field of laser interference precision measurement, and in particular relates to a real-time normalization correction device and method for PGC demodulation of a sinusoidal phase modulation interferometer. Background technique [0002] The sinusoidal phase modulation interferometry performs sinusoidal modulation on the optical path difference of the interferometer, and demodulates the interference signal by using phase-generated carrier (PGC) demodulation technology, which has the advantages of simple phase modulation, high measurement accuracy, and strong anti-interference ability. , has become an important high-precision measurement technology in the fields of displacement, vibration, surface topography, and micro-angle measurement. PGC demodulation technology has the advantages of high sensitivity, large dynamic range and good linearity. Its phase carrier can be generated by internal modulation and external modu...

AI Technical Summary

Problems solved by technology

It is usually necessary to move the measured target for several interference fringe cycles before the experiment starts, and obtain the normalization coefficient offline according to the peak-to-peak value of the orthogonal signal, but this method is not suitable for static targets, such as absolute distance measurement

In addition, during the measurement process, the normalization coefficient will change due to the drift of the phase modulation depth or the change of the measured displacement, so that the coefficient obtained by offline estimation is no longer accurate, thereby reducing the measurement accuracy

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