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

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.