Adaptive Optics
Closed-Loop Control System
Conventional Adaptive Optics methodology is used for the calibration phase of a Dynamic Optics system, i.e. to process observations from a wavefront sensor, to calculate the wavefront error, and to calculate the output signal to drive the deformable mirror to correct for wavefront error.
Wavefront Sensors
Wavefront sensing is a measurement technique that determines the surface profile of the optical wavefront. For imaging systems the wavefront surface is usually determined at the entrance or exit pupil, where the ideal diffraction-limited wavefront surface would be flat. Once the difference between the ideal and distorted wavefront is known then its phase conjugate (mirror image) can be applied to a wavefront modulator to correct the distortion.
There are many different wavefront sensing techniques, but the most widely used technology is the Shack-Hartmann sensor, an array of lenslets (also called micro-lenses) positioned in front of a 2-D detector array, such as a CCD, onto which spots formed by the lenslets from localized samples of the incident wavefront. Translation of spot positions from their reference positions is proportional to local wavefront curvature.