Interferometry of absolute distances of laser probe relief meters with harmonic wavelength deviation

The results of modeling a self-mixing laser (autodyne) as a laser probe for controlling microdisplacements are presented. A method for measuring the absolute distance from the ratio of the amplitudes of the harmonics of the autodyne signal spectrum is proposed. The calculation was carried out using the PyCharm IDE software environment and the numpy and matplotlib software modules. The measurement accuracy was estimated taking into account the accuracy of measuring the power of the autodyne signal and the amplitudes of the spectral harmonics at various deviations of the wavelength of the laser autodyne. It is shown that due to the ambiguity of the Bessel functions included in the algorithm, in order to reliably determine the distance, it is necessary to limit the choice of spectral components to the region of uniqueness, which is located at the end of the significant region of the spectrum. The error in determining the absolute distance from the deviation of the laser wavelength was studied. It was also found that as the distance to the reflector decreases, it is necessary to increase the deviation of the laser radiation wavelength so that the set of measured harmonics is in the high-frequency region. It is shown that in the deviation range from 0.1 nm to 1 nm at a distance of 50 to 100 mm, the measurement accuracy can reach several microns. The promise of using a laser autodyne is due to the task of developing laser probes for monitoring microdisplacements in a narrow range of distances to the reflector.