Optical pumping in dense atomic media: Limitations due to reabsorption of spontaneously emitted photons

Sektion Physik, Ludwig-Maximilians Universität München D-80333 München, Germany

Received: 11 November 1998
Accepted: 7 January 1999

Abstract

Resonant optical pumping in dense atomic media is discussed, where the absorption length is less than the smallest characteristic dimension of the sample. It is shown that reabsorption and multiple scattering of spontaneous photons (radiation trapping) can substantially slow down the rate of optical pumping. A very slow relaxation out of the target state of the pump process is then sufficient to make optical pumping impossible. As model systems an inhomogeneously and a radiatively broadened 3-level system resonantly driven with a strong broad-band pump field are considered.