Wavefront Sensing for High Scintillation Environments

High scintillation environments pose additional sensor burdens on conventional wavefront sensors, mainly; impaired branch cut phase estimation particularly when used in closed loop AO systems. A Self Referencing Interferometer, which measures phasedirectly, is seen as potentially providing superior performance in these high scintillation discontinuous phase environments. The sensors use a single mode fiber to filter the reference beam, provide four-bin phase retrieval phase shifting, and provides amedium for amplification of the weak reference signal. A very high gain fiber amplifier is initially required before the AO loop is closed to increase the reference signal and improve fringe visibility to an adequate level allowing the loop to finallyclose. This original concept failed to work as well as hoped because the amplification introduced significant amplified spontaneous emission, high levels of shot noise, and reduced fringe visibility. This proposal presents alternatives to the high gainamplification by integrating a Hartmann sensor in a way that enhances the SRI measurement. This proposed hybrid sensor provides information that can be processed in either way. This Phase I effort proposes to explore the merits of direct phasemeasurements and study alternatives to further enhance the SRI sensor concept. It is anticipated that the resulting wavefront sensor would have greatly improved closed loop performance in the presence of high scintillation atmospheric environments overconventional systems currently used or recently proposed.