AO4ELT5 Proceedings

Wavefront sensing detectors: 2 decades of technological progress

Feautrier, Philippe (IPAG)

New disruptive technologies are now emerging for detectors dedicated to adaptive optics. The detectors needed for this kind of applications need antonymic characteristics: the detector noise must be very low but at the same time must also sample the fast temporal characteristics of the signal. This paper describes the new fast low noise technologies that have been recently developed for adaptive optics. The first technology is the Avalanche PhotoDiode (APD) infrared arrays made of HgCdTe. In this paper are presented the two programs that have been developed in that field: the Selex Saphira 320x256 and the 320x255 RAPID detectors developed by Sofradir/CEA LETI in France. Status of these two programs and future developments are presented. Sub-electron noise can now be achieved in the infrared using the e-APD technology. The exceptional characteristics of HgCdTe APDs are due to a nearly exclusive impaction ionization of the electrons, and this is why these devices have been called "electrons avalanche photodiodes" or e-APDs. These characteristics have inspired a large effort in developing focal plan arrays using HgCdTe APDs for low photon number applications such as active imaging in gated mode (2D) and/or with direct time of flight detection (3D imaging) and, more recently, passive imaging for infrared wave front correction and fringe tracking in astronomical observations. A commercial camera solution called C-RED One, based on Selex Saphira and commercialized by First Light Imaging, is presented here. In addition, First Light Imaging also developed the C-RED 2 InGaAs 640x512 400 fps infrared camera for lower budgets. In the visible, another disruptive technology is showing outstanding performances: the Electron Multiplying CCDs (EMCCD) developed mainly by e2v technologies in UK. The OCAM2 camera, commercialized by First Light Imaging, uses the 240x240 EMMCD from e2v and is now routinely and successfully implemented on several world class telescopes.

DOI: 10.26698/AO4ELT5.0177- Proceeding PDF

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