Using ultrafast laser excitation and time-correlated single-photon counting techniques, we have measured the collisional mixing rates between the rubidium fine-structure levels in the presence of gas. A nonlinear dependence of the mixing rate with density is observed. We find Rb fine-structure transfer is primarily due to binary collisions at densities of , while at greater densities, three-body collisions become significant. We determine a three-body collisional transfer rate coefficient () of at .
© 2010 Optical Society of America
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