# Acousto-optic deflector

An acousto-optic deflector (AOD) spatially controls the optical beam. In the operation of an acousto-optic deflector the power driving the acoustic transducer is kept on, at a constant level, while the acoustic frequency is varied to deflect the beam to different angular positions. The acousto-optic deflector makes use of the acoustic frequency dependent diffraction angle, where a change in the angle ${\displaystyle \Delta \theta _{d}}$ as a function of the change in frequency ${\displaystyle \Delta f}$ given as,[1]

${\displaystyle (12)\ \Delta \theta _{d}={\frac {\lambda }{\nu }}\Delta f}$

where ${\displaystyle \lambda }$ is the optical wavelength and ${\displaystyle \nu }$ is the velocity of the acoustic wave.

AOD technology has made practical the Bose–Einstein condensation for which the 2001 Nobel Prize in Physics was awarded to Eric A. Cornell, Wolfgang Ketterle and Carl E. Wieman.[2] Another application of acoustic-optical deflection is optical trapping of small molecules.

AODs are essentially the same as acousto-optic modulators (AOMs). In an AOM, only the amplitude of the sound wave is modulated (to modulate the intensity of the diffracted laser beam), whereas in an AOD, both the amplitude and frequency are adjusted, making the engineering requirements tighter for an AOD than an AOM.