Adaptive Optics for Extremely Large Telescopes 4 – Conference Proceedings

The recent discovery of electron initiated avalanche photodiodes (e-APDs) using mercury cadmium telluridesemiconductor materials has permitted a significant advance in short-wave infrared imaging. In the visible spectrum,electron-multiplying charge-coupled devices (EMCCDs) improved imaging techniques—especially in the life sciences.And yet, no significant breakthroughs have been made in infrared imagery since the hybridization of III-V or II-VIsemiconductors with low bandgap on complementary metal-oxide semiconductor (CMOS) read-out integrated circuits(ROICs).In 2012, Philippe Feautrier et al.[1] and Gert Finger et al. [2] of the European Southern Observatory (ESO; Garching,Germany) reported successful hybridization of HgCdTe e-APDs on CMOS ROICs with a significant number of pixels(320 × 256). Feautrier et al. [3] also reported the use of a Sofradir/CEA-LETI APD array on the ESO Very Large TelescopeInterferometer (VLTI), called RAPID, demonstrating for the first time the successful operation of this technology in arepresentative environment.First Light Imaging [4] is the first commercial company to make e-APD infrared array technology available in its C-REDOne camera. Using a 320 × 256, 2.5 μm cutoff wavelength HgCdTe e-APD array deeply cooled to 80 K with a highreliabilitypulse-tube cryocooler (mean-time between failure or MTBF of approximately 90,000 hours), the camera has ahigh readout speed of 3500 frames/s (full frame) while exhibiting a readout noise below one electron—thanks to the APDgain in the range of 1 to 60.This paper reports on the results of the Sofradir/CEA-LETI RAPID program [5] and on the development of the C-REDone infrared camera from First Light Imaging based of the SELEX SAPHIRA detector [6]. The interest of ShortWavelengths InfrRed (SWIR) e-APD versus more classical HgCdTe arrays as infrared tilt sensors or pyramid wavefrontsensor like what is currently developed at Keck Observatory is also discussed in this paper.