Temperature Dependence of Rb 5P Fine-Structure Transfer Induced by $^{4}$He Collisions

Employing ultrafast laser excitation and time-correlated single-photon counting, we have measured the fine-structure transfer between Rb 5P states induced by collisions with $^{4}$He buffer gas at temperatures up to 150$^{o}$C. The temperature dependence of the binary cross-section agrees with earlier measurements while having almost an order of magnitude smaller uncertainty. Our data show that the temperature dependence of the three-body rate is about the same as that of the binary rate. The three-body rate can be described as arising from the reduction of the rubidium fine-structure splitting due to nearby helium atoms. Our fine-structure transfer studies are relevant for understanding alkali-inert gas atomic interactions as well as for practical applications in alkali laser development.