Raman Cooling of Atoms in an Optical Dipole Trap

We have Raman cooled sodium atoms below the photon recoil temperature in a novel type of blue-detuned optical dipole force trap. In this trap $4.5\times {10}^5$ atoms have been cooled to an effective three dimensional temperature of 1.0 μK at a final density of $4\times {10}^{11}{\mathrm{cm}}^{-3\mathrm{}}$. No atoms were lost during the cooling process. The phase space density increased by a factor of 320 over the uncooled sample. This is the highest phase space density achieved by an all-optical cooling method.