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An acousto-optic modulator (AOM) is a device which can be used for controlling the power, frequency or spatial direction of a laser beam with an electrical drive signal. It is based on the acousto-optic effect, that is, the modification of the 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. A piezoelectric transducer attached to the crystal is used to excite a sound wave with a frequency of the order of 100 MHz. Light can then experience Bragg diffraction at the traveling periodic refractive index grating generated by the sound wave; therefore, AOMs are sometimes called Bragg cells.

Applications include

• Q switching of solid-state lasers. In most cases, the zero-order (not diffracted) beam is used under lasing conditions, and the AOM is turned on when lasing should be prohibited.

• Cavity dumping of solid-state lasers, generating nanosecond pulses.

• Pulse picker for reducing the pulse repetition rate of a pulse train.

• In laser printers and other devices, an AOM can be used for modulating the power of a laser beam.

• Since the diffraction angle depends on the acoustic frequency, one can scan the output beam direction by changing the modulation frequency.

This example shows the correct physics principles with just a few refractive index periods. Manufactured components can be much larger and can be modeled with the same principle as the application library example Diffraction Grating.