Modeling and Direct Observation of Opto-Acoustic Interactions in an AOM

Acousto-optic modulators (AOMs) are ubiquitous tools in modern optics, serving as intensity modulators, frequency shifters, and components in laser stabilization systems. They also provide a simple and illustrative example of three-wave mixing (3WM). Because the optical and acoustic wave vectors must satisfy phase-matching conditions for specific diffraction orders, the underlying physics resembles nonlinear optical processes, light-matter interaction or cold atom mechanisms. Moreover, the required experimental setup can be realized using readily available, off-the-shelf components, highlighting the accessibility of such a project. We present a model predicting diffraction-order intensities as a function of angular misalignment between acoustic and optical wave vectors; we validated the model by performing systematic sweeps of acoustic frequency, amplitude, and incidence angle. Using time-resolved imaging combined with a 4-f Fourier filtering system, used to single out the first diffraction mode, we directly visualized the propagation of acoustic pulses through the AOM crystal. This experiment offers valuable hands-on experience with several key concepts in modern optics, including wave propagation, diffraction, and nonlinear interactions.