Very long storage times and evaporative cooling of cesium atoms in a quasielectrostatic dipole trap

We have trapped cesium atoms over many minutes in the focus of a ${\mathrm{CO}}_2$-laser beam employing an extremely simple laser system. Collisional properties of the unpolarized atoms in their electronic ground state are investigated. Inelastic binary collisions changing the hyperfine state lead to trap loss, which is quantitatively analyzed. Elastic collisions result in evaporative cooling of the trapped gas from 25 $\mu \mathrm{K}$ to 10 $\mu \mathrm{K}$ over a time scale of about 150 s.