Wavefront sensors serve two primary functions. The first, as a beam diagnostic, was explored in preceding chapters. The second, as a means of controlling adaptive optics, will be taken up here. Adaptive optics cover a wide range of applications. They can be used to control piston in optical phased arrays (such as PHASAR), provide beam steering (or pointing), correct for focus errors, or generate a "phase conjugate" of higher aberrations. It is this latter function that usually springs to mind when the term âadaptive opticsâ is used these days. The image conjured is of a mirror surface that can be warped to provide compensation for an aberrated input beam as illustrated in Fig. 9.1. These mirrors are called deformable or "rubber" mirrors.
The common means of warping the mirror is via an array of piezoelectric stacks as shown in Fig. 9.2. Under an applied voltage the stack can change its axial length. This applies a force normal to a thin mirror face plate which then bends or deforms at the attachment point.
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