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Published September 25, 2012 | Published
Book Section - Chapter Open

Read noise for a 2.5μm cutoff Teledyne H2RG at 1-1000Hz frame rates


A camera operating a Teledyne H2RG in H and Ks bands is under construction at Caltech to serve as a near-infrared tip-tilt sensor for the Keck-1 Laser Guide Star Adaptive Optics system. After imaging the full field for acquisition, small readout windows are placed around one or more natural guide stars anywhere in the AO corrected field of view. Windowed data may be streamed to RAM in the host for a limited time then written to disk as a single file, analogous to a "film strip", or be transmitted indefinitely via a second fiber optic output to a dedicated computer providing real time control of the AO system. The various windows can be visited at differing cadences, depending on signal levels. We describe a readout algorithm that maximizes exposure duty cycle, minimizes latency, and achieves very low noise by resetting infrequently then synthesizing exposures from Sample Up The Ramp data. To illustrate which noise sources dominate under various conditions, noise measurements are presented as a function of synthesized frame rate and window sizes for a range of detector temperatures. The consequences of spatial variation in noise properties, and dependence on frame rate and temperature are discussed, together with probable causes of statistical outliers.

Additional Information

© 2012 SPIE. September 25, 2012. This investigation was initially funded by the Thirty Meter Telescope, as part of a larger design study for the On-Instrument Low-Order Wavefront Sensor for the TMT Infrared Imaging Spectrograph. The performance demonstration led to an NSF ATI grant to construct, TRICK, the NIR Tip Tilt sensor for the Keck-1 AO system feeding OSIRIS. This in turn supported continued refinement of the readout algorithm and deeper understanding of the noise processes. This paper has been cleared for public release under the ITAR regulations by the US Department of Defense, Office of Security Review (ref. #4 12 S-2750, Aug 14, 2012).

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