Pair-absorption-pumped barium laser

Abstract
This is the first reported demonstration of the use of pair-absorption transitions for optically pumping lasers. In a mixture of barium and thallium metal vapors, single-photon absorption of 3867-Å laser light caused simultaneous excitation of colliding ground-state atoms to the Ba (6s6p P11°) and Tl(6p P23/2°) excited states. Excited-state densities of about 1014 cm−3 were created, and subsequent laser emission on the Ba(6s6p P11°)→Ba(6s5d D12) atomic transition at 1.5 μm was observed.