Étude d'un déphaseur achromatique ' damier ' dans un interféromètre à frange noire pour la caractérisation future des planètes extrasolaires

摘要

Direct detection of exoplanets is mandatory in order to characterize them. However, this is a hard task because of the small angular separation and high contrast between the host star and the planet. Nulling interferometry is one possible way, but it require an achromatic phase shifter. In this thesis a new phase shifter is studied, "the chessboards ". It is two mirrors or glass plate made of several cells, which position and phase shift are constrained by a mathematical scheme. The main effect is that for a given attenuation, the spectral bandwidth spreads as the number of cells in the chessboards increases, which gives the chessboards a quasi achromatic behavior. An automated test bench has been built in order to measure the attenuation produced by the chessboards in the visible. The first results have been obtained with chessboards made by photolithography on a glass plate, and an attenuation of 500 has been measured with a white laser beam. The cells' phase shift errors are the major source of loss of performance. Those generated by the fabrication process being irreversible, one chose to work with a segmented mirror that allows us to control the phase shift of each cells. In order synthesize the chessboards, the control of each cells' phase shift is mandatory and achieved by strioscopy. Thus, one can measure the chessboards behavior with respect to the wavelength, and experimentally validate the quasi-achromatic behavior of the chessboards.