Question

(i) Describe, using a sketch, the principle of operation of a Shack-Hartmann wave- front sensor.

Answer 1

Characterization of imaging system is done by Shack- Hartmann wareport sensor. It is usually used in adaptive optics systems. It has many array of lesses (called lenslet) of same focal length. Each one of them is focussed on a photon Sensor (typically a charge coupled device (CCD) or quad-cell). If sensoris placed at geometric focal plane of lenslot and is uniformly illuminated, then integrated gradient of warefoont across the lenslet is proportional to displacement o centroid. Any phase alberration can be approximated by a set of discrete tilts. Sampling warefront with an array of lenslets, all of these local tilts can be measured and whole wavefort can be reconstructed since only tits are measured Shack- Hartman cannot detect discretinuons steps in wareport. a perturbed wavefort flenslet army. ecD the image plane Schematic illustration operation of single lenslet.