Transient compression of a MOT and high intensity fluorescent imaging of optically thick clouds of atoms

We describe a way to compress Cs atoms in a MOT to temporarily reach spatial densities of 10¹² atoms/cm³. The method entails starting off with more atoms than will ultimately be used, and then changing parameters so the atoms rush toward the trap center. For some time during the compression, collisional losses at the center are more than offset by newly arriving atoms. We monitor the compression with a high intensity fluorescent technique that is well suited to providing accurate number and density measurements for large dimension clouds that are very optically thick.