Long spin relaxation times in a single-beam blue-detuned optical trap

A scheme to trap atoms in a blue-detuned optical dipole trap, formed with a single laser beam and a holographic phase plate, is demonstrated. 10(5) rubidium atoms are trapped for (1/e lifetime) similar to 300 msec, at temperatures of similar to 24 mu K and a density of similar to 7x10(11) atoms/cm(3). for a trapping beam detuning of 0.1-30 nm. The time for a trapped atom to scatter one photon off the trapping beam is measured and found to he linear in the trapping laser detuning. At a detuning of 0.5 nm from resonance this time was measured to be similar to 100 msec, indicating that the atoms are exposed on average only to similar to 1/700 of the maximal light intensity in the trap. The use of a single laser beam allows far simple dynamical changes of the potential and large adiabatic compressions, while keeping the atoms mainly in the dark. [S1050-2947(99)50903-7].