Diffraction-limited observations of astronomical sources with a rotation shearing interferometer in the near infrared

We present an experiment aimed at diffraction-limited imaging of astronomical sources in the 2-5 μm range. It is based on a rotation shearing interferometer that produces fringes in the pupil plane that can be scanned through the zero optical path difference. The two-dimensional interferograms are recorded with an infrared camera looking at the recombined pupil image. The modulus and the phase of the Fourier transform of the object intensity distribution are derived from these interferograms. The main advantage of this technique is its constant transfer function that makes it independent of seeing variations and instrumental aberrations. We describe the experiment set-up and discuss some simulation results which illustrate the operation of the interferometer. We present astronomical data recently obtained at the 4.20m William Herschel Telescope of the Royal Greenwich Observatory in La Palma, and results on the circumstellar shell star NML Cygni.