Ultracold 88Sr atoms for an optical lattice clock

This paper reports results of cooling and trapping of Sr-88 for future use in an optical lattice clock. Strontium atoms are cooled to ultra-cold temperatures using a two-stage cooling process. In the first stage, atoms are captured from a Zeeman-slowed atomic beam and cooled to 2 mK in a magneto optical trap operated on the S-1(0) - P-1(1) transition at 461 nm. The second cooling stage utilizes the spin forbidden S-1(0) - (3)p(1) transition at 689 nm. To reach ultra-cold temperatures, 50 ms of broadband cooling is followed by 28 ins long single frequency cooling. The transfer efficiency from the first to the second cooling stage was measured to be 23%, leaving 7 x 10(6) atoms at a temperature of 1 mu K. The atomic cloud is overlapped with a horizontally oriented 1-D far-off resonance optical dipole trap (FORT) at 813 nm with an effective potential depth of 25 mu K. Due to equal light shifts of the S-1(0) and the (3)p(1), state simultaneous Doppler cooling during the atom loading into the FORT is possible which leads to a transfer efficiency into the dipole trap of up to 60 %.