acousticoptical

Acousticoptical, commonly written acousto-optical, refers to the interaction between acoustic (sound) waves and optical (light) waves within a material. The effect arises from the photoelastic or elasto-optic response of the medium: a traveling acoustic wave modulates density and refractive index, creating a moving diffraction grating for light. When a light beam encounters this grating, it is diffracted, and in many configurations the diffracted light carries a frequency shift equal to the acoustic frequency.

The interaction is typically described in Bragg geometry, where the optical and acoustic waves satisfy a diffraction condition that depends on the material’s refractive index, the acoustic frequency, and the interaction length. Diffraction efficiency, beam deflection, and frequency shift can be tuned by adjusting the acoustic power, frequency, and crystal orientation. The underlying mechanism is the electrostriction-driven modulation of the optical path, making the acousto-optic effect a fast, solid-state means of light control.

Materials commonly used in acousto-optic devices include tellurium dioxide (TeO2), lithium niobate (LiNbO3), quartz, fused silica, GaP, and ZnSe. TeO2 is favored for high diffraction efficiency and wide angular acceptance, while LiNbO3 offers good electro-optic compatibility and integration potential. A typical device employs a piezoelectric transducer bonded to a crystal, launching an acoustic wave that acts as the dynamic grating.

Devices based on acoustic-optics include acousto-optic modulators (AOMs) and acousto-optic deflectors (AODs). They are used for rapid intensity modulation, frequency shifting of laser light, and beam steering in imaging, spectroscopy, laser machining, lidar, and telecommunications.

Limitations include insertion loss, thermal sensitivity, and wavelength dependence of efficiency; higher power and multi-pass configurations can mitigate some drawbacks but introduce complexity and heating concerns.