1. Development of a high-speed single photon pixellated detector for visible wavelengths Introduction A photon incident on the photocathode produces a photoelectron. The electron is accelerated over a high voltage and is incident on the Si. A resulting charge cloud is created in the Si detector. The charge cloud is collected and read-out by the Medipix. Values above threshold increment the internal counter. The number of counts per pixel per acquisition is read out by Medipix, through the ceramic header to the interface PCB. Ceramic Header Interface PCB e-e- Si Detector Medipix Photon High Voltage 5-10kV Photocathode LNS20 Vacuum tube Ceramic header provides. A pad for attachment of the Medipix detector assembly. Wirebonding pads for the chip which connect to wire traces. Wire traces which lead to drilled feed- through vias in the ceramic. Three offset dielectric layers to protect the vacuum against micro-cracks in the metal layers. A back surface containing a metal layer for the attachment of surface mount components and connectors. A surface on which to braze the flange onto which the vacuum tube can be attached. Many biological imaging applications require high frame rates at low light intensities. Currently the EMCCD is the camera of choice but limits the frame rates to ~500fps. We present the design of a camera capable of true single photon counting across an array of 256x256 pixels at frame rates, over 3000fps, higher than ever achieved for similar arrays. Within the region 1-10 3 photons lies techniques such as single cell fluorescence, and the imaging of Ca 2+ signalling. These techniques and many others are critical to the imaging and understanding Maximum spatial frequencies transferred are limited by the Medipix. Minimising the distance of the photocathode to the Medipix chip and maximising the accelerating voltage decreases the effect of the point spread function of the photocathode. In the design chosen the separation is set at 2.27mm for a maximum voltage of 10kV. Optical Imaging with Medipix Ceramic Header Imaging Performance Conclusions We present the design of a detector capable of imaging low intensity light at unprecedented speeds. These high-speeds are achieved with SNR performance comparable to that of the highest performance EMCCD, in fact a higher quantum efficiency photocathode would allow our detector to out-perform the EMCCD on SNR. MTF curves show that we can expect 30% contrast at spatial frequencies up to ~15 line pair/mm. Aaron Mac Raighne 1, Antonio Teixeira 2, Jason McPhate 3, John Vallerga 3, Pierre Jarron 2, Colin Brownlee 4, Val O’Shea 1 1. Department of Physics and Astronomy, University of Glasgow, Scotland. 2. CERN, Genève, Switzerland. 3. University of California, Berkeley, U.S.A. 4. The Marine Biological Association of the United Kingdom, Plymouth, England of cellular and neural networks. They are limited by the acquisition speeds of current low intensity detector technology. The Medipix chip contains 256x256 pixels each with a square pixel size of side length 55 µm. The input accepts positive or negative charge. The preamplifier has a gain ~13mV/1 ke -, a peaking time of 150ns and a return to of baseline<1µs, giving a count rate of 1MHz. An energy window is set by upper and lower thresholds. A 13-bit counter per pixel is electronically shuttered when the chip is reading out. Using a clock of 100MHz and the parallel read-out the entire chip can be read-out in 266µs which makes possible the high frame rates Medipix Figures: (a) Shows the results of simulations demonstrating the effect of the distance between the photocathode and the Medipix chip. By multiplication of the calculated MTF of the Medipix with the results of figure (a) the MTF for the system is found and displayed in figure (b). Figures (c) and (d) show the MTFs calculated for both the photocathode and the full detector system at a separation of 2.27mm for increasing values of the accelerating voltage (a) (b) (c)(d) Ceramic disc Drilled vias filled with Au Dielectric layer Au layer Metal layer for surface mount devices and connectors