Linear Avalanche HgCdTe Arrays for Photon Counting AO Wavefront Sensing

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Since the mid 1990's, Adaptive Optics (AO) techniques have revolutionized ground-based observational astronomy at optical and infrared (IR) wavelengths. The precise sensing of the atmosphere's distortion of the wavefront from a natural or laser guide star is crucial to achieving a telescope's diffraction limit. Dr. Donald Hall of the University of Hawaii proposes to adapt, and optimize for AO wavefront sensing, sensors developed through the nation's substantial investment in space and military LADAR by producing modest format arrays and demonstrating their photon counting performance for wavefront sensing at the telescope. To achieve this, the technique utilizes the unique linear avalanche properties of HgCdTe, a substance already the material of choice for astronomy in the 1 - 5 micron waveband and the technology base for production of large format arrays for near-IR astronomy. The project will hybridize 32x32 arrays of HgCdTe linear-mode avalanche photo-diodes to an optimized 64-output readout. These hybrids will count individual near-IR photons with wavelengths between 0.85 and 2.5 microns with high quantum efficiency, at frame rates approaching 100 KHz, and with no degradation of their fundamental Poisson statistics. The goal is to produce over a thousand readout dies and to make several dozen high-quality hybridized arrays available for initial characterization followed by deployment in telescope AO systems.While the proposed investigation has the potential to revolutionize AO wavefront sensing and all aspects of the science it enables on ground based telescopes, it barely taps the surface of broader applications that extend beyond astronomy. The investigation will also encompass potential solar applications and likely enabling coronal AO sensing. Finally, society will benefit from the development of the technique, its application beyond astronomy, and the exciting scientific discoveries it will make possible.Funding for development and construction of the prototype spectrograph is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.