An acousto-optic modulator (AOM), also called a Bragg cell or an acousto-optic deflector (AOD), uses the acousto-optic effect to diffract and shift the frequency of light using sound waves (usually at radio-frequency). It is based on the acousto-optic effect, i. the modification of the refractive index of some crystal or glass material by the oscillating. An acousto-optic modulator consists of a piezoelectric transducer which creates sound waves in a material like glass or quartz. Within these devices incoming light Bragg di racts o acoustic wavefronts which propagate through a crystal.