All-optical runaway evaporation to Bose-Einstein condensation

We demonstrate runaway evaporative cooling directly with a tightly confining optical-dipole trap and achieve fast production of condensates of 1.5×10⁵ ⁸⁷Rb atoms. Our scheme uses a misaligned crossed-beam far off-resonance optical-dipole trap (MACRO-FORT). It is characterized by independent control of the trap confinement and depth allowing forced all-optical evaporation in the runaway regime. Although our configuration is particularly well suited to the case of ⁸⁷Rb atoms in a 1565 nm optical trap, where an efficient initial loading is possible, our scheme is general and will allow all-optical evaporative cooling at constant stiffness for every optically trappable atomic or even molecular species.