Image Processing Reference
In-Depth Information
40
Chapter 4
This chapter discusses wavefront compensation devices and their common ap-
plications, with an emphasis on those used for beam steering and image stabiliza-
tion.
4.2 Wavefront Compensation
Wavefront compensators can be separated into two classes: those that correct for
high-order aberrations and those that correct for lower-order aberrations. Within
these two groups, the devices can be separated based on their speed or bandwidth of
operation. Typically, low-order aberrations such as piston and tip and tilt are large
amplitude effects and require just one or two degrees of freedom to compensate.
Higher-order aberrations are often much lower in amplitude, but require a large
number of correction elements (degrees of freedom) to compensate. Most high-or-
der correctors have the ability to compensate for some of the low-order aberrations
as well, but do not have the dynamic range to correct both low- and high-order aber-
rations simultaneously.
Astronomical telescope systems have become one of the most successful appli-
cations of wavefront compensation (Hardy 1998). Figure 4.1 shows a schematic
layout of an adaptive optics system at Mount Wilson Observatory (Thompson and
Teare 2002). This diagram shows each stage in compensating the aberrations in a
Figure 4.1
An adaptive optics system illustrating the separated tip-tilt mirror and the
deformable mirror for correcting low and high spatial frequency aberrations, respec-
tively.
