POLARIZATION-GRADIENT-ASSISTED SUBRECOIL COOLING - A QUANTUM CALCULATIONS IN ONE-DIMENSION

We present a fully quantum-mechanical analysis of laser cooling of an angular momentum J(g) = 1 to J(e) = 1 transition in a laser configurat ion consisting of two counterpropagating linearly polarized laser beam s. The essential feature of this configuration is the coexistence of v elocity-selective coherent population trapping (VSCPT) and polarizatio n-gradient cooling. The role of polarization-gradient cooling is to pr ovide (i) for short interaction times ''precooling'' of the initial mo mentum distribution and (ii) in the long-time limit ''confinement of v elocities.'' This eventually leads to a larger number of atoms being c aptured in the dark state when compared with the scheme of Aspect et a l. [Phys. Rev. Lett. 61, 826 (1988)]. We find that the optimum paramet er values for polarization-gradient cooling and VSCPT are in a complet ely different parameter regime: polarization-gradient cooling works be st off resonance and for low intensities, while VSCPT works best on re sonance. We can combine the advantages of polarization-gradient coolin g and VSCPT in a scheme where we cycle in time between the optimum coo ling parameters for both cooling mechanisms.