We have systematically studied a simple technique that accurately determines number of atoms in a magneto-optical trap. Absorption energy of a laser field that interacts with cold atoms is a direct measurement of atom number. The measured energy neither depends on the detuning, intensity, and polarization of the laser field nor is affected by other system parameters. Our work also demonstrates that such technique can be applied to study the phenomenon of coherent population trapping.

• Received 30 March 2001

DOI:https://doi.org/10.1103/PhysRevA.64.031401