Two-photon-excited stimulated emission from atomic oxygen in flames and cold gases.

We report detection of stimulated emission from the atomic-oxygen 3 (3)P-3 (3)S transition at 845 nm after two-photon excitation of the 2 (3)P-3 (3)P transition using 226-nm laser radiation. We study this stimulated emission process in flames and in room-temperature flows of O(2) and N(2)O and compare its behavior with that of fluorescence signals acquired simultaneously. Rapid depletion of the laser-excited state by the stimulated emission process may have an impact on the use of diagnostic techniques based on multiphoton excitation in oxygen and in other species. The strength of the stimulated emission signal suggests that it may have applications as a diagnostic technique.