Measurement Results Detector concept works! Flood fields show MCP fixed pattern noise that divides out Spatial resolution consistent with theory (Nyqvist sampling of 55  m pixels) Parameters can be tuned to optimize spot size Detector Concept 1. High-QE photocathode (GaAs) converts incoming photons. 2. Two microchannel plates (MCP) in chevron configuration amplify photo-electron (gain between several thousands to millions). 3. Charge cloud gets detected by the Medipix2 pixel circuits. If detected charge > threshold --> pixel counter gets incremented. 4. Noiseless chip readout after programmable shutter time. Medipix2* photon counting pixel readout ASIC: 256 x 256 pixels, 55  m square window discriminator, 14-bit counter per pixel 3-side buttable (512 x 512 arrays), serial (LVDS) or parallel readout (32-bit CMOS bus; 266  100 MHz) ~500 transistors/pixel; 0.25  m CMOS technology Developed within the framework of the Medipix Collaboration; Tube Fabrication for WFS ‘PRIAM’ Parallel Readout Board Five 32-bit parallel input ports to read out max. 5 Medipix2 chips in <290  s (clock 100 MHz) XILINX FPGA for data arrangement, optional flat field and dead time correction as well as data reduction (e.g. spot coordinates) provides all control signals and voltages 4 bi-directional 1.6 Gbit/s links  total readout time 660  s Motivation Adaptive Optics are indispensable for new generation ground- based telescopes! Detectors for wave-front sensors (WFS) require large pixel arrays (512 x 512), noise <3e - per pixel, high quantum efficiency (QE) and kHz frame rates* Current CCDs have high QE, but must trade noise performance and array size for speed * Angel, R. et al. ‘A Roadmap for the Development of Astronomical Adaptive Optics’, July 6, 2000; A Noiseless Kilohertz Frame Rate Imaging Detector Based on Microchannel Plates Read out with the Medipix2 CMOS Pixel Chip Point-like objects get blurred by turbulences in the atmosphere. WFS measure the atmospheric turbulences, send this information to deformable mirrors that compensate online for the distortions. Shack-Hartman correction method using an equally spaced lenslet array. AO reveals a previously undetected star in the Orion cluster. The surface plot shows the dramatic increase in intensity and sharpness.    take 2 indepen- dent uniform illuminations (flood fields) histogram Flood field (500 Mcps).Ratio = flood1 / flood2. Histogram of ratio is consistent with counting statistics. increase shutter time Test pattern; 100  s exposure. The spots correspond to individual photon events. Test pattern; 1 s exposure. Group 3-2 visible ~9 lp/mm. Spot area versus rear field.Spot area versus Medipix2 low threshold. A.G. Clark, D. Ferrère, D. La Marra, B. Mikulec - University of Geneva, Switzerland J.B. McPhate, O.H.W. Siegmund, A.S. Tremsin, J.V. Vallerga - SSL Berkeley, USA J. Clement, C. Ponchut, J.-M. Rigal - ESRF Grenoble, France GaAs photo- cathode MCP pair Medipix2 chip