Commissioning of cryogenic preamplifiers for SAPHIRA detectors

SAPHIRA detectors, which are HgCdTe linear avalanche photodiode arrays manufactured by Leonardo, enable high frame rate, high sensitivity, low noise, and low dark current imaging at near-infrared wavelengths. During all University of Hawaii Institute for Astronomy lab testing and observatory deployments of SAPHIRA detectors, there was approximately one meter of cables between the arrays and the readout controllers. The output drivers of the detectors struggled to stably send signals over this length to the readout controllers. As a result, voltage oscillations caused excess noise that prevented us from clocking much faster than 1 MHz. Additionally, during some deployments, such as at the SCExAO instrument at Subaru Telescope, radio-frequency interference from the telescope environment produced noise many times greater than what we experienced in the lab. In order to address these problems, collaborators at the Australia National University developed a cryogenic preamplifier system that holds the detector and buffers the signals from its outputs. During lab testing at 1 MHz clocking speeds, the preamplifiers reduced the read noise by 45% relative to data collected using the previous JK Henriksen detector mount. Additionally, the preamplifiers enabled us to increase the clocking frequency to 2 MHz, effectively doubling the frame rate to 760 Hz for a full (320x256 pixel) frame or 3.3 kHz for a 128x128 pixel subarray. Finally, the preamplifiers reduced the noise observed in the SCExAO environment by 65% (to essentially the same value observed in the lab) and eliminated the 32-pixel raised bars characteristic of radio-frequency interference that we previous observed there.