FORCE, DIFFUSION, AND CHANNELING IN SUB-DOPPLER LASER COOLING

We present an extensive set of measurements on one-dimensional sub-Dop pler cooling and channeling in counterpropagating light beams. The exp erimental method consists of the measurement of the profile of an init ially subrecoil collimated atomic beam, which is deflected by the inte raction with the light field. The initial velocity of tile atoms in th e direction of the laser beams is varied in the range -1 less than or equal to upsilon(perpendicular to)(ms(-1))less than or equal to 1 by c hanging the angle between atomic and laser beams. Fur the orthogonal c ircular polarization (sigma(+)sigma(-)) sub-Doppler cooling configurat ion, the force and the diffusion coefficient characterizing the coolin g process have been determined as a function of the initial velocity u psilon(perpendicular to) from the average deflection and broadening of the atomic beam profile. We observe transient effects due to the slow evolution of the distribution over the magnetic sublevels to an equil ibrium. The experimental results agree very well with quantum Monte Ca rlo simulations and semiclassical calculations. For the orthogonal lin ear polarization (pi(x) pi(y)) configuration, we demonstrate the valid ity of tile well-known Sisyphus picture for the cooling mechanism by c omparing the experimental data to the results of a simple semiclassica l Monte Carlo model incorporating only the dipole force and optical pu mping. In weak standing waves of either circular or linear polarizatio n, we demonstrate the characteristic features of channeling.