Positive gain measurements on the 3350-Å continuum band of Hg2

Abstract

A He‐Cd⁺ laser operating at 3250 Å and an Ar⁺ laser at 3511 Å and 3638 Å have been used to probe for gain on both sides of the Hg₂ 3350‐Å (A³1_u→X¹Σ_g⁺) continuum band in Hg vapor at a pressure of 3.75 atm that was pumped by a 1.5‐MeV 600‐J 20‐nsec electron beam. This letter presents the first observation of positive gain on this 3350‐Å band of Hg₂. The results indicate that the stimulated emission cross section for this band is larger than any associated photoionization process in the Hg vapor and has a magnitude of approximately 10⁻¹⁸ cm². Also, raising the temperature of the vapor above its saturation value increases the maximum value and duration of the observed gain, indicating that the population of the upper level of this transition is being fed by a temperature‐dependent internal energy reservoir in the Hg.