Radiation trapping in sodium-noble-gas mixtures

Measurements of cesium mixing and quenching cross sections in methane gas: understanding sources of heating in cesium vapor lasers

Accurate modeling of the operation of diode-pumped alkali lasers is a critical step toward the design of high-powered devices. We present precision measurements for the Cs-CH₄ 6²P_3/2 → 6²P_1/2 mixing cross section and the 6²P_3/2,1/2 → 6²S_1/2 quenching cross section, which are important parameters in understanding the operation and, in particular, the heat generated in a cesium vapor laser. Measurements are carried out using ultrafast laser pulse excitation and observation of fluorescence due to collisional excitation transfer in time is done using the technique of time-correlated single-photon counting. Mixing rate measurements are acquired over methane pressures of 10 - 40 Torr, resulting in a Cs-CH₄ 6²P_3/2 → 6²P_1/2 mixing cross section of (1.40 ± 0.08) × 10^-15 cm², while quenching rate measurements are carried out over methane pressures of 500 - 4000 Torr, resulting in a 6²P_3/2,1/2 → 6²S_1/2 quenching cross section of (1.57 ± 0.03) × 10^-18 cm². These results suggest only a slight contribution to the heating of a cesium vapor laser is due to Cs 6²P quenching, contrary to previous studies. We also discuss additional possible sources of energy transfer from upper excited states of Cs.

Precursor luminescence near the collapse of laser-induced bubbles in alkali-salt solutions

A precursor luminescence pulse consisting of atomic line emission is observed as much as 150 nanoseconds prior to the collapse point of laser-created bubbles in alkali-metal solutions. The timing of the emission from neutral Na, Li, and K atoms is strongly dependent on the salt concentration, which appears to result from resonant radiation trapping by the alkali atoms in the bubble. The alkali emission ends at the onset of the blackbody luminescence pulse at the bubble collapse point, and the duration of the blackbody pulse is found to be reduced by up to 30% as the alkali-salt concentration is increased.