Abstracts Category : Other

Dead-time effects in photon counting

by Doo Jin Cho

Dead-time effects are investigated in the contextof photon counting. Simple models of nonparalyzable and paralyzablecounters are considered in the general framework of renewalprocesses. Closed-form expressions for the autocorrelationfunctions for both nonparalyzable and paralyzable counters areobtained. The "input-dependent" counter model is also considered,and a set of fundamental partial integro-differential equations,which can be used to determine the counting statistics, has beenderived. </br>For the microchannel-plate (MCP)imaging detector, the dependence of dead-time effects on the sizeof illumination area was investigated experimentally. As anoperational model, we propose the independent-paralyzable-countermodel, IPCM, which assumes that each microchannel behaves as anindependent paralyzable counter. For the detector with an MCPassembly of "V-Z" configuration the dead time increases rapidly asthe illumination area increases, which indicates that the couplingbetween microchannels is important. However, for a singlecurved-channel MCP, the IPCM gives a good agreement withexperimental results. We have also performed an experiment with achannel electron multiplier, and found that it behaves as a singleparalyzable counter. It may be concluded that the coupling observedin the "V-Z" MCP device is due to the complex structure of thedevice rather than due to the intrinsic property of the MCP. </br>As an application we theoreticallyinvestigated both global and local dead-time effects on linearfiltering in quantum-limited image recognition. An expression forthe probability density of photodetection at a specified spatialposition is derived when the local dead-time effects are included.For detailed images, it is found that local dead-time effects havesignificant effects on the recognition capability at a high countrate. </br>Also dead-time effects were applied tothe generation of sub-Poissonian and antibunched light. Anoptoelectronic device, which can generate either thenonparalyzable or the paralyzable dead-time effect, has beenconstructed using a feedback scheme in conjunction with theacousto-optic deflector. "Semi-classical" experiments show a goodagreement with theoretical predictions.