A CHEMICALLY DRIVEN VISIBLE LASER TRANSITION USING FAST NEAR-RESONANT ENERGY-TRANSFER

Evidence is obtained which demonstrates the potential for developing purely chemical visible lasers based on rapid near-resonant energy transfer from metastable excited triplet states of germanium and silicon monoxide (a3Σ+, b>3II) to select metal atoms. In this study, the Group IIIA metal atoms were chosen as the energy receptors for the energy transfer-pump sequence. Excited triplet states were generated from the Ge-O3, Ge-N2O, Si-N20, and Si-NO2 reactions; the bulk of the experimental results was obtained with a germanium-based system. The energy stored in the long-lived triplet states is transferred to pump X2P1/2 thallium, indium, and gallium atoms to their lowest lying 2S1/2 states; the process with thallium and gallium atoms appears particularly efficient. Adopting a pumping sequence in which a prcmixed Ge-TI atom combination is oxidized, we observe a system temporal behavior which suggests the creation of a population inversion producing a gain condition and forming the basis for full cavity oscillation on the Tl 72S1/2-62P3/2 transition at 535 nm. In an extremely efficient energy transfer, GeO metastables formed in the Ge-O3 reaction rapidly pump those Tl atoms with which they are intimately mixed to populate the 251/2 excited state, creating a temporary population inversion with respect to the upper X2P3/2 component of the ground 2P thallium atom configuration. This sequence produces an intense short-lived photon pulse whose intensity can exceed by an order of magnitude that associated with Tl 2Sl/2-1P3/2 fluorescence. Based upon the extent of the reaction-energy transfer zone, a system parameterization suggests that at minimum, we have observed a superfluorescent laser pulse (versus amplified spontaneous emission) created on the Tl 72S1/2-61P3/2 transition whose duration in a self-terminating sequence does not exceed 5 ns FWHM. (A similar, albeit less pronounced, effect is observed in the chemically more complex Ga-Ge-03 system.) Of the eight possible ways to combine the germanium-based reactants outlined above to obtain an energy transfer pump of Tl or Ga atoms, only those sequences involving the oxidation of a premixed metalloid-metal mixture display the manifestation of what appears to be a superfluorescent event; the results suggest that this sequence allows for the rapid interaction of a high concentration of the pumping metalloid oxide and Group IIIA metal on a time scale comparable to the 2Sl/2 radiative lifetime. The current observations are in excellent agreement with those results obtained previously in the study of “superradiance” from Tl discharges. The observation of a gain condition is further substantiated when the single-pass Ge-Tl-O3 system is converted to a multipass oscillator configuration (~3% output coupling) with a corresponding increase of up to ten times the output power of the single-pass configuration, a substantial increase in the ratio of superfluorescence to fluorescence, and the display of a significant directionality. This approach, which makes use of fast intermolecular energy transfer, shows the promise of extrapolation to several additional systems whose radiative lifetimes greatly exceed those of 2Sl/2 Tl and Ga atoms. © 1990 IEEE