Acousto-optical method for measuring the displacements of a laser beam in two directions orthogonal to its axis

Abstract

The issues of improving the method for controlling the two-coordinate displacements Δly and Δlz of a laser beam in the OY and OZ directions orthogonal to its OX axis are considered. It is proposed to use a fiber photodetector with a micro-optical lens at the input of the light guide to register the interference picture produced in the Fresnel zone by the first and zero diffraction orders formed by an acousto-optical (AO) modulator. In the method, it is proposed to use a prismatic optical scheme placed in front of a single-axis AO modulator for a laser beam displaced Δly and Δlz along two axes OY and OZ, forming two output beams. For the first beam, displacements along the OY axis are excluded: Δly-var, Δlz=0, and the second beam is rotated relative to the first beam by 90° around the OX axis (i.e., Δly→Δlz) with the same exception of displacements along the OY axis with the achievement of the following: Δly=0, Δlz-var. This technique allows you to use a single-axis (1D) AO modulator to control the two-coordinate (2D) displacements Δly, Δlz of the initial laser beam. We also discuss the implementation of a differential measurement method by using two phase measuring devices: an interpolator and a phase meter, and the effect of signal noise on the resolution.