A high-speed quadrature-phase rotation shearing interferometer for imaging through turbulence

A new technique of rotation shearing interferometry has been developed, which is optimized to reduce systematic problems when imaging through turbulence. Key improvements over previous systems are a high-frame-rate, low-noise camera and an optical system which generates four instantaneous interferograms, with instrumental phase shifts of 0°, 90°, 180°, and 270°. The simultaneous quadrature-phase interferograms enable an instantaneous complex visibility measurement in every frame. The camera system has a very short readout time, permitting high duty-cycle recording of short-exposure images, and allows tracking of individual turbulent structures as they translate across the interferograms. By eliminating sources of systematic errors and maximizing the coherence time available, astronomical measurements that far exceed what is possible using ordinary interferometric or direct-imaging techniques are attainable. Laboratory demonstrations as well as first fringes at the Palomar 200" telescope will be discussed.