LASER COOLING OF MOLECULES - A SEQUENTIAL SCHEME FOR ROTATION, TRANSLATION, AND VIBRATION

A novel scheme is proposed for sequential cooling of rotation, transla tion, and vibration of molecules. More generally, this scheme manipula tes and controls the states and energies of molecules. The scheme, whi le somewhat complex, is simpler and more feasible than simply providin g a large number of synchronously but independently tunable lasers. Th e key component is a multiple single frequency laser (MSFL) in which a single narrow band pump laser generates an ensemble of resonant ''sti mulated Raman'' (RSR) sidebands (subsequently amplified and selected) in a sample of the molecules to be cooled. Starting with a relatively cold molecular sample (e.g., a supersonic beam of Cs-2), the rotation of molecules is cooled by sequential application of P branch electroni c transition frequencies transverse to the molecular beam beginning at higher rotational angular momentum J. Then translation of molecules i s cooled by application of multiple low J, P, and R branch transition frequencies which counterpropagate with the molecular beam and are syn chronously chirped over their Doppler profiles. Finally, vibration of molecules is cooled by blocking the R(0) line of the 0-0 band. Only th is specific order of rotation-translation-vibration appears feasible ( using molecules produced by photoassociation of ultracold atoms avoids the requirement for translational cooling). Each step employs true di ssipative cooling (i.e., reduction of system entropy in three degrees of freedom) by spontaneous emission and should yield a large translati onally cold sample of molecules in the lowest (upsilon=0, J=0) level o f the ground electronic state, suitable for studies such as molecule t rapping, ''molecule optics,'' or long range intermolecular states. (C) 1996 American Institute of Physics.