Ellipticity and astigmatism compensation in a double-pass AOM setup via the generalized ABCD matrix approach

The acousto-optic modulator (AOM) is one of the most commonly used devices in modern AMO experiments and time and frequency metrology. In free-space double-pass configurations, AOMs allow precise frequency control while preserving beam pointing stability. Unfortunately, they also introduce beam ellipticity, astigmatism and phase distortions that may significantly degrade coupling efficiency to ultrahigh-finesse optical cavities.

In this seminar, a generalized ABCD matrix formalism describing Gaussian beam propagation through free-space AOM systems will be presented. Based on this approach, a modified double-pass configuration employing a spherical mirror and anamorphic prism pair was developed in order to generate circular and astigmatism-free laser beams.

The theoretical model was experimentally verified for two commonly used wavelengths, 780 nm and 1560 nm, showing good agreement between simulations and measured beam parameters. The obtained results demonstrate that quantitative engineering of beam propagation in AOM systems may significantly simplify alignment procedures and improve spatial beam quality in experiments relying on high-finesse optical cavities.

The presented approach is particularly motivated by optical flywheel systems used in modern time and frequency metrology, but may also find applications in a broad range of AMO experiments employing free-space AOMs.