Research On Picometer Resolution Phase Subdivision For Heterodyne Laser Interference Signals

With the develop of high-tech such as gravitational wave detection, surface science and extreme ultra violet lithography in recent years, the requirements of measurement resolution for heterodyne laser interferometer has changed from nanometer and sub nanometer level to tens of picometer level even picometer level. Facing the new 101-100 level measurement resolution challenge, the measurement resolution of traditional frequency/period/time difference phase measurement method can’t break through 0.1nm. Quadrature lock-in amplifier phase measurement method is increasingly valued who can achieve 1 pm displacement measurement resolution in theory. On the one hand the theoretical error model has not been effectively established which cause the working parameters can not be accurately designed, on the other hand the existing quadrature lock-in amplifier phase measurement method can only be used in static and quasi static measurement situation which can not meet the needs of ultra precision dynamic measurement.On the basis of analysising the theory of quadrature lock-in amplifier phase measurement, this thesis establishes the signal flow of the method and phase measurement error of the whole model. And through the simulation analysis this thesis gets the influence of working parameters of each module on measurement resolution and measurement bandwidth in the quadrature lock-in amplifier phase measurement system. This thesis emphatically solves the DC bias, sum digital filter of frequency component and dynamic noise suppression who effect the measurement resolution and measurement bandwidth. The main research works of the thesis are as follows:Firstly, this thesis establishes the signal flow and phase measurement error of the whole model of quadrature lock-in amplifier phase measurement. Through numerical simulation, analysis the working characteristics of data acquisition, hardware multiplier, sum frequency component digital filter, antitangent digital demodulation in the quadrature lock-in amplifier phase measurement system who effect the measurement resolution and measurement bandwidth. On this basis, combined with the specific needs of data acquisition speed, data acquisition resolution, DC bias compensation, inhibition ratio of sum frequency and difference frequency, word length of antitangent digital demodulation, this thesis puts forward overall design scheme of picometer resolution phase subdivision for heterodyne laser interferometer system who can achieve 15 pm displacement measurement resolution and maximum 1.5m/s measurement speed.Due to the problem that traditional quadrature lock-in amplifier phase measurement uses the narrow bandwidth filter to ensure high inhibition ratio of sum frequency and difference frequency, this thesis uses high bandwidth linear phase FIR digital filter at first. By slightly relax inhibition ratio of sum frequency and difference frequency, the maximum measurement speed of the system is raised to 1.5m/s by mm/s and high resolution and high speed dynamic measurement of displacement is realized. Due to the problem high frequency noise caused by slightly relaxing inhibition ratio of sum frequency and difference frequency, this system add Kalman filter to phase output link to effectively reduce the noise of output phase.Finally, use electrical simulation method to test heterodyne laser interferometer signal subdivision card based on quadrature lock-in amplifier phase measurement theory. Experimental shows that hardware multiplier, sum frequency component digital filter and antitangent digital demodulation module in the quadrature lock-in amplifier phase measurement system achieve the expected design goals. The whole system achieves 0.03°angle resolution which equivalents to 27 pm displacement resolution and the the maximum measurement speed of the system is 1.5m/s. In the measurement range, the static standard deviation of displacement measurement results is less than 10 pm and dynamic standard deviation is less than 27 pm which demonstrate the validity of the measurement resolution of the system.