Direct two-color photoassociative ionization in a rubidium magneto-optic trap

We report the observation of direct, two-color photoassociative ionization (PAI) in collisions between ⁸⁵Rb atoms optically cooled and confined in a magneto-optical trap. We also measure the resulting R₂⁺ ion spectrum and compare it to earlier trap-loss fluoresecence spectra. Unlike PAI in Na, which ionizes principally by collisional autoionization, the Rb₂* intermediate photoionizes directly to Rb₂⁺ in a fixed optical field. These observations confirm PAI as a sensitive and broadly applicable spectroscopic tool.