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Phase measurement of a segmented wave front using PISton and TILt interferometry (PISTIL).

New architectures for telescopes or powerful lasers require segmented wave front metrology. This paper deals with a new interferometric wave front sensing technique called PISTIL (PISton and TILt), able to recover both piston and tilts of segment beams. The main advantages of the PISTIL technique are the absence of a reference arm and an access to the tilt information. An explanation of the principle, as well as an experimental implementation and the use of a segmented active mirror, are presented. Measurement errors of λ/200 for piston and 40 µrad for tilts have been achieved, well beyond performances requested for the above mentioned applications.