Cold-atom gas at very high densities in an optical surface microtrap

An optical microtrap is realized on a dielectric surface by crossing a tightly focused laser beam with a horizontal evanescent-wave atom mirror. The nondissipative trap is loaded with $\sim {10}^5$ cesium atoms through elastic collisions from a cold reservoir provided by a large-volume optical surface trap. With an observed 300-fold local increase of the atomic number density approaching ${10}^{14}{\mathrm{cm}}^{-3},$ unprecedented conditions of cold atoms close to a surface are realized.