Two-colour photoassociation spectroscopy of ultracold sodium

We demonstrate a number of two-colour spectroscopy techniques where the first step is the photoassociation of laser-cooled and trapped sodium atoms to form bound states of Na-2. High-resolution (similar to 0.001 cm(-1)) spectra of Na-2 are obtained. Spectra of the 0(g)(-) (3S + 3P(3/2)) 'purely long-range' state demonstrates the use of two-colour spectroscopy to open up an ionization channel for detecting the occurrence of photoassociation. The utility of photoassociation as a technique for producing cold molecular samples in a well defined rovibrational state is demonstrated with spectra showing bound --> bound and bound --> free (Condon internal diffraction) transitions after the photoassociation. Starting from states in the 0(g)(-) and 1(g) (3S + 3P(3/2)) potentials, these transitions include upward transitions to autoionizing potentials dissociating near 3P + 3P and downward transitions back to the 3S + 3S ground-state potentials. Spectroscopic constants for six levels of a doubly excited 1(u) state of Na-2 are given.