Experimental Observation of Optically Trapped Atoms

We report the first observation of optically trapped atoms. Sodium atoms cooled below ${10}^{-3\mathrm{}}$ K in "optical molasses" are captured by a dipole-force optical trap created by a single, strongly focused, Gaussian laser beam tuned several hundred gigahertz below the $D_1$ resonance transition. We estimate that about 500 atoms are confined in a volume of about ${10}^3$ μ${\mathrm{m}}^3$ at a density of ${10}^{11}$-${10}^{12}$ ${\mathrm{cm}}^{-3\mathrm{}}$. Trap lifetimes are limited by background pressure to several seconds. The observed trapping behavior is in good quantitative agreement with theoretical expectations.