Laser cooling at high density in deep far-detuned optical lattices

We report a way to overcome heating due to the reabsorption of scattered light when relatively many atoms are laser cooled at high density. A sample of 8×10⁷ Cs atoms, with 6×10¹¹ atoms cm^-3, is loaded into a deep far-detuned one-dimensional optical lattice, which acts as a large volume three-dimensional (3D) trap. Polarization gradient cooling with a separate set of cooling beams is found to work well in this trap, populating the trap’s vibrational ground state with more than half the atoms. After cooling, the lattice is shut off adiabatically, leaving a still dense sample at 1.2 μK. We propose and demonstrate a generalization to a 3D lattice, which will allow many more atoms to be loaded into conservative light traps, and can greatly increase the initial phase-space density for loading magnetic traps.