An acousto-optic deflectors (AOD) primary goal was laser beam deflection to realize a large number of resolvable spots so that it may be used to replace mechanical scanners such as the rotating polygons.
In recent years most of the effort was directed toward Bragg cells for optical signal processing applications.
But finally nowadays Acousto-optic deflectors have many advantages over electro-mechanical devices, such as fast response time, high precision, and stability of a raster obtained.
Acousto-optic deflectors provide a simple solid state scanner which eliminates the inherent drawbacks of mechanical scanners due to moving parts such as facet errors and the requirement of realignment because of bearing wear.
Acousto-optic deflectors find many applications based on continuous laser beam deflection (one axle (1D) as well as 2 axis (2D)) and vector (random) scanning.
The most interesting, demanded and important applications are:
- laser tweezers;
- RGB systems for laser projectors;
- laser scanning microscopy and profilometry;
- measurements of surfaces of specimens over some predefined grid of points.
Main deflector principles
As a rule, light diffraction on the wave of slow shear acoustic mode in crystallographic surface (110) is used in paratellurite to provide most efficiency of acousto-optical interaction.
Typical construction acousto-optic cell made on the basis of paratellurite is shown on picture. The phase velocity of the sound wave is normal to the plane of transducer and directed at the angle α with respect to crystallographic direction . The sound energy flow vector does not coincide with the corresponding wave vector, due to high acoustic anisotropy present in the paratellurite crystals. Angle of sound energy drift A is quiet big and can reach 70 degrees that should be taken into consideration for cell geometrical sizes calculations.