The wavefront of the first-order diffracted beam, however, is modified to match the desired shape of the test surface.

The acousto-optic medium must be designed carefully to provide maximum light intensity in a single diffracted beam.

Here is the wavefunction of the diffracted beam and is the so called structure factor which is given by:

The Ewald sphere construction will determine the diffracted beams to be seen and the scattering angles at which they will appear.

Hence, the intensity of the sound can be used to modulate the intensity of the light in the diffracted beam.

In addition, the phase of the diffracted beam will also be shifted by the phase of the sound wave.

Rotating the sample changes the intensity of the diffracted beams due to their dependence on the azimuth angle.

This zero intensity for a group of diffracted beams is called a systematic absence.

The smaller the aperture, the larger the spot size at a given distance, and the greater the divergence of the diffracted beams.

The cross section of the diffracted beam may or may not be identical to the one of the incident beam.