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What is Acousto optic modulator frequency shift, formula

This page describes Acousto optic modulator frequency shift and also mentions Acousto optic modulator (AOM) frequency shift formula.

Introduction:
Acousto optic modulator works based on Acoustic optic effect. This effect deals with modulation of optical property through variation of refractive index of the medium under the influence of acoustic wave.

What is Acousto Optic Modulator?

Acousto Optic Modulator

All the Acousto Optic devices work based on photo-elastic effect or by interaction of acoustic waves and light in the crystalline material. An acoustic waves are generated in the crystal by application of RF drive signal to piezo-electric transducer. This creates areas of compression and refraction in the crystal bulk. This causes periodic changes in the refractive index. As a result light input to AO (Acousto Optic) device is diffracted into number of orders at the output. The acoustic wave travels from transducer to absorber. It is used to prevent creation of secondary diffractions due to reflections.

Most of the Acousto-optic (AO) devices are designed to maximize diffraction of input laser beam into a single first order position. The device is then said to be operating in the Bragg regime and requires the AO device to be correctly aligned and the drive power adjusted at or below the RF saturation level. Also refer acousto optic modulator basics and working >> for more information.

Acousto optic modulator frequency shift formula or equation

The diffracted beam is frequency shifted from the incident laser beam or light beam by an amount equal to the RF frequency (f). By changing the orientation of the AOM (Acousto optic modulator) with respect to the incident beam, the diffracted beam can be produced at frequencies fL+f or fL - f.
➨ Frequency shift = fL +/- f
Where,
fL is the laser frequency and f is the RF frequency used to produce acoustic wave.
The frequency shift depends on conservation of momentum by interaction of laser beam and acoustic wave.



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