Pathlength Stability of Synthetic Aperture Telescopes - the Case of the 25 cm CERGA Interferometer

Abstract

Synthetic aperture telescopes are more and more considered as a promising scheme for the next generation of Very Large Telescopes : the basic idea is to combine the beams of two or more independent telescopes. The question immediately raising when considering such a technique is the pathlength stability and the amount of pathlength difference that can be tolerated, assuming a reasonable bandwidth, to preserve coherent addition of the wavefronts and hence, high spatial frequencies observations. To that respect the I2T (two telescopes interferometer) in operation at CERGA constitutes a remarkable test-bench for studies of mechanical, optical and atmospheric constraints that are to be faced when dealing with amplitude interferometry between several telescopes.