Advances in Bichromatic Force Slowing of Atoms and Molecules

The optical bichromatic force (BCF) holds promise as an efficient, simple, and compact means to slow atoms and molecules to MOT capture velocities.\footnote{M. Cashen and H. Metcalf, JOSA B \textbf{20}, 915 (2003).}$^,$\footnote{M. A. Chieda and E. E. Eyler, PRA \textbf{84}, 063401 (2011).} Metastable helium beams, with $v\sim1000$~m/s, are especially worthwhile atomic candidates since they presently require Zeeman slowers with lengths of 2--3~m. We present a novel BCF decelerator in which the Doppler shifts are chirped to keep the force centered on the atoms as they slow. This is made possible by recent advances in high-power diode lasers and electronics, and avoids many of the problems of alternative designs using large detunings. Initial tests on He* atoms show encouraging results. Unlike atoms, direct laser slowing of molecules remains exceedingly difficult, although success with SrF has very recently been reported.\footnote{J. F. Barry, E. S. Shuman, E. B. Norrgard, and D. DeMille, to be published.} We calculate that for molecules with near-cycling transitions, rapid laser BCF slowing should be possible.\footnote{Chieda, op. sit.} For the CaF molecule, we predict slowing by $\Delta v = 150$~m/s, enough to bring a buffer-gas cooled beam to rest. An experimental demonstration is in progress.