Physical Review A
Collisional modification of the atomic-Na 3s 2 S1/2 –5s 2 S1/2 two-color two-photon polarization spectrum
LeRoy F. Cook, D. A. Olsgaard, Mark D. Havey, A. Sieradzan
Abstract
An experimental investigation of the atomic-Na 3s $^{2}$${\mathit{S}}_{1/2--}$5s $^{2}$${\mathit{S}}_{1/2}$ two-color two-photon polarization spectrum has been made. Measurements of the linear polarization degree of the two-photon transition were made for one laser tuned within a \ifmmode\pm\else\textpm\fi{}100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ range of the atomic-Na 3p $^{2}$${\mathit{P}}_{\mathit{j}}$ levels, with the second adjusted to satisfy the two-photon resonance condition. The relatively short-pulse (\ensuremath{\sim}0.5 ns) lasers used eliminate effects on the spectrum due to atomic-Na hyperfine interactions and radiation trapping, while greatly reducing depolarization due to collisions with Ar gas. In the absence of collisions, the measured polarization spectrum is in excellent agreement with calculations. Measurements of the Ar pressure dependence of the spectrum revealed strong depolarization in the vicinity of resonant excitation through the 3p $^{2}$${\mathit{P}}_{3/2}$ level. A collisional depolarization cross section of 200(30) \AA{} for this process was deduced from the data.