Phase measurement of 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 PISTIL technique introduces a breakthrough for such metrology by removing the need for a reference arm, and by giving access to the tilt information. After an explanation of the principle, we present an experimental implementation and apply it to characterize a segmented active mirror. Measurement errors of λ/200 for piston and 40µrad for tilts have been achieved, well beyond performances requested for its potential applications.