A photon-counting camera system developed from a crossed-strip detector

A crossed-strip detector initially developed at UC Berkeley’s Space Sciences Laboratory has been demonstrated as a laboratory benchtop instrument and is now in the process of being integrated by Los Alamos National Laboratory into a portable, real-time, single-photon-counting camera system. The crossed-strip detector consists of 32 anode strips along each of two axes sealed inside a vacuum tube behind a photocathode and a microchannelplate stack. A photon incident on the photocathode produces a cloud of charge from the microchannel plates that falls onto a portion of the 64 anode strips, producing a signal on a subset of channels along each axis and requiring that all anode channels continually be analyzed simultaneously. To maximize the photon flux that can be accepted by the sensor with minimal deadtime, the crossed-strip sensor has been combined with shortershaping- time amplifiers and higher-rate digitizers than previously used. With the ultimate goal of reaching 100 million events per second, FPGA-implementable algorithms have been developed for the identification of pulses on each anode channel and the determination of the pulses’ time and amplitude. From the pulse times and amplitudes, a charge cloud can be reconstructed and the centroid determined to produce the time and position of each incident photon. The data-analysis procedure will be discussed, measurements detailing the performance of the camera system as it exists at this point will be presented, and the planned layout of the embedded camera system hardware will be detailed.