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Acousto-optic modulator (AOM), aka Bragg cell, is a device which allows the frequency, intensity and direction of an input laser beam to be modulated. It is based on the acousto-optic effect, i.e. the change of refractive index by the oscillating mechanical pressure of a sound wave. The key element of an AOM is a transparent crystal (or piece of glass) through which the light propagates and a transducer attached to it used to excite a sound wave with a frequency on the order of 100 MHz, i.e. radio frequency. Modulation of this incoming light can be achieved by varying the amplitude and frequency of the acoustic waves travelling through the crystal. This can be simple ON/OFF modulation for fast switching or variable level modulation to provide proportional intensity control. These modes are determined by the RF driver type; digital or analog modulation respectively (or a combination of both). AOMs are used to control laser beam intensity, frequency of laser beam, in active mode locking, Q-Switching & cavity dumping of solid state lasers.