Wavefront sensing for adaptive optics J. P. Lancelot Chellaraj Thangadurai [Ph.D Thesis]

Doctor of Philosophy Indian Institute of Astrophysics, Bangalore 2007

A wavefront sensor in an adaptive optics system, measures the phase changes across the telescope pupil of the incident beam. The estimate of these errors is later used in a closed loop correction system to achieve close to diffraction limited optical quality. A new wavefront sensor based on polarization shearing interferometry technique using two crossed Babinet Compensators (BC) has been developed and studied. The necessary theory for shearing interferometry using BC has been developed. Simulations of the interferometric records were carried out for the study of various aberrations in an optical system and the effect of noise, ripple and atmospheric turbulence in the interferograms. The geometry of the optical set up for carrying out the laboratory experiments using Shack Hartmann and Polarization Shearing Interferometer wavefront sensors in the same set up have been described. The data reduction procedure for the estimation of wavefront errors from a single interferometric record using Fourier technique has been worked out. The actual results obtained from the laboratory experiments for both the sensors have been compared. The method provides a convenient alternative choice for wavefront sensing in an actual adaptive optics system for astronomical telescope. The suitability of this new wavefront sensor is highlighted.