Optical gain in a neutron-induced 3He-Ne-O2 plasma

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Abstract
A single pass gain of ∼0.9% p/m (at 8446 Å in atomic oxygen) has been measured for a 3He‐Ne‐O2 plasma generated by the volumetric 3He(n,p)3H reaction induced by neutrons from a pulsed nuclear reactor. The plasma was contained in an optical cavity containing a chopping fan that permitted a measurement of the ratio of output 8446 Å from the normal cavity to that with the back mirror blocked. This ratio, called the unblocked‐blocked ratio, was used to study the gain dependence on total pressure and concentration. The maximum gain observed was for a concentration of 0.048% O2 and 1.5% Ne, at a total pressure of 600 Torr. The peak gain remained fairly constant with neutron fluxes from 1013 to 2.5×1015 n/cm2 sec. Results of other concentration studies are also discussed. The laser medium is pumped by thermal neutrons from the Illinois TRIGA reactor that impinge on a 80‐cm by 0.8‐cm‐i.d. glass tube containing from 50 to 800 Torr 3He‐Ne‐O2.