Overview of the SAPHIRA detector for adaptive optics applications

We discuss some of the unique details of the operation and behavior of Leonardo Selex avalanche photodiode for HgCdTe infrared array (SAPHIRA) detectors, particularly in relation to their usage for adaptive optics wavefront sensing. SAPHIRA detectors are 320 × 256 at 24-μm pixel HgCdTe linear avalanche photodiode arrays and are sensitive to 0.8- to 2.5-μm light. SAPHIRA arrays permit global or line-by-line resets of the entire detector or just subarrays of it, and the order in which pixels are reset and read enables several readout schemes. We discuss three readout modes; the benefits, drawbacks, and noise sources of each; and the observational modes for which each is optimal. We describe the ability of the detector to read subarrays for increased frame rates and, finally, clarify the differences between the avalanche gain (which is user-adjustable) and the charge gain (which is not).