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An
acousto-optical material is one for which the refractive index can be changed
by the density fluctuations (strain) produced by an acoustic wave. The
change in the dielectric constant, el,
is related to the mechanical strain, e,
through the photoelastic coefficient, p, such that: D(1/el
) = pe.
If
a longitudinal acoustic wave is sent through an acousto-optically active
solid, it establishes a density grating in the material that will diffract
a light beam in the manner shown below. The diffracted beam will not be
present if there is no acoustic signal (only the transmitted beam will
remain) and the device can, therefore, act as an optical switch. The table
shows some parameters of optoacoustic substances. |
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