Determination of anisotropy-dependent inelastic collision cross sections in atomic sodium using linear polarization spectroscopy

Abstract

We report on the measurement of the linear polarization degree of the $3s{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ $\ensuremath{\rightarrow}$ $3p{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{3/2}$ $\ensuremath{\rightarrow}$ $5s{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ transition in atomic sodium. A linearly polarized pump laser creates an alignment in the excited ${}^{23}$Na $3p{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{3/2}$ level. From the spectra, we extracted the inelastic collision cross section for the disalignment of the excited atoms by collisions with ground-level argon or xenon atoms. Measurements were done by monitoring the intensity of the cascade fluorescence from the $4p{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2}$ $\ensuremath{\rightarrow}$ $3s{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ transition at 330.29 nm, in the presence of Ar and Xe for pressures ranging from 5.3 to 146.6 mbar. We demonstrated that the polarization measurement can provide important information about the alignment-dependent inelastic process in alkali-metal\char21{}rare-gas collisions. A depolarization cross-section value of 196 (22) \AA{}${}^{2}$ for Na-Ar and 357 (21) \AA{}${}^{2}$ for Na-Xe are obtained.