High-Pressure Fine-Structure Mixing and Quenching Rates in a Rb-He Mixture

In this research, we report measurements of fine-structure mixing and quenching rates for rubidium and helium gas mixtures at high He buffer gas pressures and a range of temperatures. Pulses from a Ti-Sapphire mode-locked laser tuned to the D2 transition (λ = 780 nm) was used to excite Rb to the 5P_3/2 state. Collisional mixing subsequently populated the 5P_1/2 state and the D1 fluorescence (λ = 795 nm) was detected using a photomultiplier tube (PMT). The photon time-of-flight was determined using a time-to-digital converter (TDC), and the measurement was repeated at a frequency of 500 kHz. The fine-structure mixing and quenching rates were determined by fitting the resulting fluorescence data to the solutions of the mixing rate equations as previously reported (1). Measurements were performed at temperatures in the range of 22-200 °C and pressures ranging from 1-20 atm. We observed a quadratic dependence of mixing rate on pressure; mixing rates also increased with temperature. Quenching rates showed no specific correlation with pressure, as the measurements taken did not follow a trend. This work may assist in optimizing the performance of high-power alkali lasers.

(1) J. F. Sell et al., J. Phys. B: At. Mol. Opt. Phys. 45 055202 (2012)