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Title: Wavefront reconstruction using polarization shearing interferometer
Authors: Mohanty, A
Issue Date: Jul-2011
Publisher: Indian Institute of Astrophysics
Citation: M. Tech. Thesis, University of Calcutta, Calcutta
Abstract: Observations with ground based telescopes suffer from atmospheric turbulence. Independent of the telescope size, the angular resolution in the visible is equivalent to that of a telescope with a diameter of 10-20cm. This effect is caused by the turbulent mixing of air with different temperature in the atmosphere. Thus, the perfectly plane wave from a star at infinity is aberrated before it enters the telescope. In the following, the physical background of imaging through turbulence, using Kolmogorov statistics, and the Polarisation Shearing Interferometry techniques to sense and to correct the wavefront aberrations with adaptive optics have been discussed. Since a wavefront sensor in an adaptive optics system is important as it measures the phase changes across the telescope pupil of the incident beam. A new wavefront sensor based on polarisation shearing interferometry technique using two crossed Babinet Compensators(BC) has been developed and studied. Simulations of the interferometric records were carried out using Matlab for the study of aberrations in an optical system and the effect of the atmospheric turbulence in the interferograms. The data was reduced from the interferogram using Fourier Transform Technique and the wavefront was reconstructed from the wavefront slope data. The Zernike polynomials coefficients were found out for various D/ro values. Experimentally, an artificial turbulent medium was created in the laboratory. Using Matlab, theoritical simulations were carried out to find the value of the Fried's parameter in the presence of a turbulent medium. Thus, this method provides an alternative choice for wavefront sensing in an actual adaptive optics system for the astronomical telescope.
Description: Restricted Access
Thesis Supervisor Dr. J . P. Lancelot
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Appears in Collections:Integrated M.Tech-Ph.D (Tech.)

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