Selective Reabsorption Leading to Multiple Oscillations in the 8446-Å Atomic-Oxygen Laser

Laser oscillation of atomic oxygen at 8446 Å occurs in four closely spaced lines with peculiar intensity ratios, all detuned from the atomic center frequencies of the three fine-structure transitions. These anomalies are caused by the selective reabsorption of resonance radiation from the lower laser level by ground-state oxygen atoms. The selectivity results from the fact that the velocity distribution of the laser levels is considerably wider than that of the ground state, because of the dissociative mode of production of excited oxygen atoms. Possible extension of this mechanism to the atomic-hydrogen system is discussed. New atomic-oxygen laser lines at 2.89, 4.56, 5.97, 6.86, and 10.40 $\mu$ are also reported and assigned.