Acoustooptics

Acoustooptics is the study and application of the interaction between acoustic waves and optical waves in transparent materials. The central phenomenon is the acousto-optic effect, in which an ultrasonic or radio-frequency acoustic wave propagating through a solid creates a moving refractive-index grating via the photoelastic effect. This grating can diffract light, producing a displaced and, in some configurations, frequency-shifted copy of the incident beam.

In typical devices, an RF transducer excites an acoustic wave that travels through a crystal such as tellurium dioxide (TeO2), lithium niobate (LiNbO3), quartz, or GaP. Light entering the crystal interacts with the traveling grating; under the Bragg condition, a portion of the light is diffracted at a characteristic angle. Diffraction efficiency depends on the acoustic power, interaction length, polarization, and optical wavelength. The regime and geometry determine whether the light is efficiently deflected or modulated.

Key devices include acousto-optic modulators (AOMs), which control light intensity, frequency, or both by adjusting the RF drive; acousto-optic deflectors, which steer beams for scanning applications; and acousto-optic tunable filters (AOTFs), which provide wavelength-selective filtering via programmable acoustic waves. These devices enable fast, solid-state optical switching, beam routing, and spectral selection in laser systems, communications, imaging, and spectroscopy.

Performance depends on material properties such as elasto-optic coefficients, acoustic attenuation, and thermal stability, as well as operating wavelength and bandwidth requirements. TeO2 is widely used for its strong interaction, though other materials may be chosen for different wavelength ranges or power handling.