Laboratory and On-sky Testing of an InGaAs Detector for Infrared Imaging

Abstract

We describe the results of testing a shortwave infrared CMOS camera using an indium gallium arsenide (InGaAs) detector. The new generation of InGaAs detectors offers a cost-effective alternative to mercury cadmium telluride (HgCdTe) for astronomy research, with current, off-the-shelf cameras requiring no modification before use. Testing was conducted in the laboratory and on-sky while mounted to the robotic, 2 m Liverpool Telescope using a H-band filter. The camera exhibits a dark current of 821 e- s-1 pix-1 and a bias level of 864 e- pix-1. The dark current associated shot noise is of similar size to the read noise of 32 e- pix-1 in one-second exposures. Linearity within the count region where readout noise and bit-depth saturation effects are not dominant is within a few tenths of a per cent. After field-compression by fore optics, the plate-scale yields 0.″3 pix-1, near perfect for Nyquist sampling at the La Palma site. The sky background for the H-band filter dominates the other noise sources for the instrument for one-second exposures producing sky-limited photometry. On-sky observations show that milli-magnitude precision is achieved for sources <10.7 mag and a signal-to-noise ratio of 10 is achievable for 16th magnitude with a 3 minutes total exposure time, making it an ideal follow-up instrument for sources detected in current and upcoming IR surveys.