Storage time of cold Rb atoms in an optical dipole trap formed by a multimode fiber laser

We systematically studied the storage time of Rb-87 atoms in an optical dipole trap (ODT) formed by a multimode fiber laser. Storage time is an important parameter in cold atom experiments. If atoms are prepared in the hyperfine state vertical bar F = 2 >, hyperfine-state-changing collisions can transfer these atoms from vertical bar F = 2 > to vertical bar F = 1 >, whereby the released kinetic energy leads to considerable trap loss. In most ODT experiments, atoms are prepared in the hyperfine state vertical bar F = 1 >. However, two-photon Raman transitions induced by high-power multimode fiber lasers can optically pump these atoms from vertical bar F = 1 > to vertical bar F = 2 >, and the following hyperfine-state-changing collision results in the trap loss. In this work, our experimental data indicate that both the two-photon Raman transition and the hyperfine-state-changing collision can be inhibited if the atoms are prepared in the single Zeeman sublevel of vertical bar F = 2, m = 2 > (or vertical bar F = 2, m = 2 >) and an auxiliary magnetic field is applied. (C) 2015 Optical Society of America