All-optical cooling of 39K to Bose-Einstein condensation.

We report the all-optical production of Bose-Einstein condensates (BEC) of 39K atoms. We directly load 3 × 107 atoms in a large volume optical dipole trap from gray molasses on the D1 transition. We then apply a small magnetic quadrupole field to polarize the sample before transferring the atoms in a tightly confining optical trap. Evaporative cooling is finally performed close to a Feshbach resonance to enhance the scattering length. Our setup allows one to cross the BEC threshold with 3 × 105 atoms every 7 s. As an illustration of the interest of the tunability of the interactions we study the expansion of Bose-Einstein condensates in the one-dimensional to three-dimensional crossover. [ABSTRACT FROM AUTHOR]