Realization of High Optical Density Rb Magneto-optical Trap

We report experimental demonstration of a magneto-optical trap (MOT) of Rb atoms with a high optical density. With 2.2-cm-diameter cooling laser beams, we achieve an optical density of nearly 11 for about 2.6×10¹⁰ trapped Rb atoms with the beam intensity of about 6.6mW/cm² per beam. The temperature of the cold atoms is about 250μK. Furthermore, by ramping the magnetic field gradient from 8G/cm to about 20G/cm, the atomic cloud in the MOT is compressed and the optical density is up to 16.