Abstract
Modern image detectors with exceptionally low readout noise of about one electron (${{\rm e}^ -}$) per pixel allow for applications with ultra-low levels of light intensity. In this Letter, we report a property of scientific CMOS detectors that makes accurate spectroscopy at ultra-low levels of illumination depending on a thorough calibration procedure. Our results reveal that pixel sensitivity to light may have significant nonlinearity at accumulation levels smaller than $50\,{{\rm e}^ -}$ per pixel. The sensitivity decreases by a factor of ${\sim}0.7$ at an accumulation level of ${\sim}1\,{{\rm e}^ -}$ per pixel and photon detection rate of about 170 Hz. We demonstrate that the nature of this nonlinearity might be quite complicated: the photoelectric response of a pixel depends on both the number of accumulated electrons and the detection count rate (at rates larger than 250 Hz).
© 2021 Optical Society of America
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