Characterization of OCam and CCD220, the fastest and most sensitive camera to date for AO wavefront sensing

For the first time, sub-electron read noise has been achieved with a camera suitable for astronomical wavefront-sensing (WFS) applications. The OCam system has demonstrated this performance at 1300 Hz frame rate and with 240×240-pixel frame rate. ESO and JRA2 OPTICON 2 have jointly funded e2v technologies to develop a custom CCD for Adaptive Optics (AO) wavefront sensing applications. The device, called CCD220, is a compact Peltier-cooled 240×240 pixel frame-transfer 8-output back-illuminated sensor using the EMCCD technology. This paper demonstrates sub-electron read noise at frame rates from 25 Hz to 1300 Hz and dark current lower than 0.01 e-/pixel/frame. It reports on the comprehensive, quantitative performance characterization of OCam and the CCD220 such as readout noise, dark current, multiplication gain, quantum efficiency, charge transfer efficiency... OCam includes a low noise preamplifier stage, a digital board to generate the clocks and a microcontroller. The data acquisition system includes a user friendly timer file editor to generate any type of clocking scheme. A second version of OCam, called OCam 2 , was designed offering enhanced performances, a completely sealed camera package and an additional Peltier stage to facilitate operation on a telescope or environmentally rugged applications. OCam 2 offers two types of built-in data link to the Real Time Computer: the CameraLink industry standard interface and various fiber link options like the sFPDP interface. OCam 2 includes also a modified mechanical design to ease the integration of microlens arrays for use of this camera in all types of wavefront sensing AO system. The front cover of OCam 2 can be customized to include a microlens exchange mechanism.