Features of Acousto-Optical Laser Displacement Interferometers with Subpicometric Resolution by Double Heterodyning of Optical Signals and Auto-Tuning of the Second Heterodyne Frequency

The article discusses acousto-optical laser displacement interferometers with frequency adapting of blocks. In the optical design, three spatially combined different-frequency optical flows are formed, illuminating the photodetector, realizing double heterodyning. Two of them are created as a result of diffraction in an acousto-optical modulator of radiation from the first stabilized laser, and the third is an amplitude-modulated optical flow of a semiconductor laser with a modulation frequency near to the difference frequency of the first two optical flows. The mode of operation with auto-tuning frequency of a semiconductor laser is discussed to reduce the difference frequency between three optical flows for photoconversion with low photodetector noise and subpicometric resolution.