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 ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ atoms optically cooled and confined in a magneto-optical trap. We also measure the resulting ${\mathrm{R}}_2^{+}$ ion spectrum and compare it to earlier trap-loss fluoresecence spectra. Unlike PAI in Na, which ionizes principally by collisional autoionization, the ${\mathrm{Rb}}_2^{\mathrm{*}}$ intermediate photoionizes directly to ${\mathrm{Rb}}_2^{+}$ in a fixed optical field. These observations confirm PAI as a sensitive and broadly applicable spectroscopic tool.