COOLING-ASSISTED AND CONFINEMENT-ASSISTED VELOCITY-SELECTIVE COHERENTPOPULATION TRAPPING USING STANDING-WAVE RAMAN EXCITATION

We show that polarization gradient cooling occurs in the A-system simu ltaneously with velocity-selective coherent population trapping (VSCPT ). Starting with a Doppler temperature sample, this process pre-cools atoms and contains them to within twice the recoil velocity, a range e fficiently capturable by VSCPT. We present a Sisyphus-type model to il lustrate the cooling mechanism; the cooling coefficient estimated from this model is in close agreement with the results we obtain numerical ly. We also present results from fully quantum simulations employing t he Bloch states, verifying the basic features of this mechanism. The s imulations show that, for sodium, this cooling may enhance the rate of three-dimensional VSCPT by 200 times over the rate achievable from Do ppler precooling alone. We estimate that in 90 ms, for example, the at oms would be cooled in three dimensions to one-tenth the recoil temper ature.