An adaptive optical system to compensate for the effects of turbulence in a laser beam, comprising:
- a steering mirror movable about multiple tilt axes and positioned to relay an incoming laser beam, the beam having a cross-section that includes multiple subapertures;
- a phase correction device positioned to receive the beam after relay by the steering mirror, wherein
- the phase correction device includes a plurality of phase correction elements,
- each of the phase correction elements corresponds to a different one of the subapertures, and
- each of the phase correction elements is positioned to induce phase corrections in its corresponding subaperture;
- a wavefront sensor (WFS) positioned to receive the incoming beam after correction by the phase correction device, the WFS including a plurality of WFS output channels, each of the output WFS channels corresponding to a different one of the subapertures;
- a focal plane array positioned to receive the incoming beam;
- and
- at least one controller configured to perform steps during a frame period that include
- (a) calculating a centroid for an image formed on the focal plane array by the incoming beam,
- (b) generating tilt commands, based on the calculated centroid, for moving the steering mirror about the multiple tilt axes,
- (c) receiving data on the WFS output channels,
- (d) correcting data received in step (c) for gain and bias of the WFS,
- (e) for each WFS output channel, calculating first and second indices to a look-up table based on the corrected data of step (d),
- (f) for each WFS output channel, obtaining a phase error value from the look-up table using the first and second indices calculated in step (e),
- (g) for each WFS output channel, subtracting a calibration phase associated with that WFS output channel,
- (h) calculating a piston based on the data received in step (c),
- (i) for each WFS output channel, subtracting a piston calculated during performance of step (h) for a previous frame period,
- (j) for each WFS output channel, subtracting tilts calculated during a previous frame period based on data from the WFS during the previous frame period,
- (k) for each WFS output channel, temporally filtering according to the equation
- d(j,k,t)=a*φ(j,k,t)+b*d(j,k,t−1)
- wherein
- d(j,k,t) is a temporally filtered phase correction for the subaperture corresponding to the WFS output channel for the frame period,
- d(j,k,t−1) is a phase correction, for the subaperture corresponding to the WFS output channel, for a previous frame period,
- φ(j,k,t) is a phase error computed as a result of performing steps (d) through (g), (i) and (j),
- a=KDC(1−b),
- b is between about 0.90 and about 0.95, and
- KDC is a desired system gain, and
- (l) correcting the result of step (k) for gain and offset of the phase correction device.