We show that the effective decay rate of Zeeman coherence, generated in a ${}^{87}\mathrm{Rb}$ vapor by linearly polarized laser light, increases significantly with the atomic density. We explain this phenomenon as the result of radiation trapping. Our study shows that radiation trapping must be taken into account to fully understand many electromagnetically induced transparency experiments with optically thick media.

• Received 31 January 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.133601