PHOTOASSOCIATION OF ULTRACOLD ATOMS: A NEW TOOL FOR MOLECULAR SPECTROSCOPY

Abstract

The field of laser cooling and trapping of atoms has had a profound impact on many areas of atomic, molecular and optical science. In particular, ultracold atoms colliding in magneto-optical traps typically have relative kinetic energies of $300\mu K (\sim 7 MHz)$, so free-bound absorption lines are as sharp as bound-bound lines. Moreover, because of very long range centrifugal barriers, only a few collisional partial waves are important ($J^{\prime\prime} = 0, 1$ and 2 in our work on $^{39}K$). Such photoassociative free-bound absorption allows observation of ``pure long-range molecule'' states ($R_{e} = 28$ and 39 {\AA} in $^{39}K_{2}$) as well as long-range levels of known short range states with outer classical turning points of $\sim 20 - 250 {\AA}$. Such spectra have been observed by ``trap loss'' (decrease in atomic fluorescence), molecular ionization, and fragment ionization. Optical-optical double resonance (OODR), e.g. through the ``Franck-Condon windows'' of the ``pure long-range'' states, produces readily assignable spectra at higher asymptotes as well. Further extensions of ultracold photoassociative spectroscopy and applications to determination of long range potentials, atomic properties, and Bose-Einstein condensate stability will be presented.