Gaseous laser power limiter initiated by nuclear radiation

Abstract

A laser protection device employing a gas plasma switch wherein applied laser radiation is focused inside a gas chamber, and a nuclear source is employed to pre-ionize the gas volume, whereupon focused laser radiation causes gas breakdown and plasma formation that attenuates the radiation. Specifically, the invention reduces the threshold of plasma switch initiation by incorporating a nuclear source within the gas chamber that constantly injects plasma forming seed particles into the vicinity of a focused laser beam. The plasma resulting from avalanche ionization of the seed particles reflects, absorbs and deflects the laser radiation. The nuclear source introduces charged particles, excimers and metastable atoms with low ionization potential into the gas chamber. Such charged particles are effective plasma initiators because they have low ionization thresholds. The present invention has been found well suited to protect against pulsed laser sources because of fast rise times and high attenuation levels. The present invention has negligible insertion loss, fast rise time on order of 5 nsec, passive operation requiring no input power using laser initiated plasma, it operates in stand-by and is ready for operation at all times, and provides broadband protection for all wavelengths greater than about 1 .mu.m.