Abstract
ABSTRACT It is known that the production of ‘sparks’ in gases by focused laser beams must involve a triggering process different from the acceleration of random free electrons responsible for conventional sparks. Photo-ionization of the gases in question requires the ‘simultaneous’ absorption of several photons by a gas atom, so that any theory invoking this effect must take account of statistical fluctuations which may carry the instantaneous photon flux at a single atom across the necessary threshold. To allow for correlations between the coherent laser photons it is proposed that they be described by a Polya (negative binomial) distribution, rather than a Poisson distribution which appreciably overestimates the mean (observable) flux associated with a given fluctuation. In a worked example a special form of the Polya distribution (the Furry distribution) is found to give remarkable agreement with the flux observed experimentally to produce ionization breakdown, provided one may assume photo-ionization ...
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