Optimized Bose-Einstein-condensate production in a dipole trap based on a 1070-nm multifrequency laser: Influence of enhanced two-body loss on the evaporation process

摘要

We present an optimized strategy for the production of tightly confinedBose-Einstein condensates (BEC) of 87Rb in a crossed dipole trap with directloading from a magneto-optical trap. The dipole trap is created with light of amultifrequency fiber laser with a center wavelength of 1070nm. Evaporativecooling is performed by ramping down the laser power only. A comparison of theresulting atom number in an almost pure BEC to the initial atom number and thevalue for the gain in phase space density per atom lost confirm that thisstraightforward strategy is very efficient. We observe that the temporalcharacteristics of evaporation sequence are strongly influenced bypower-dependent two-body losses resulting from enhanced optical pumping to thehigher-energy hyperfine state. We characterize these losses and compare them toresults obtained with a single-frequency laser at 1030nm.