Abstract

Recently, it has been demonstrated [1] that an optical pumping process could lead to sub-Doppler features in the transmission spectrum of a thin (L = 10-100µm) cell. Indeed, when the cell is highly anisotropic (thickness « beam diameter), and due to transient effects, the optical pumping (e.g. transfer to a transparent hyperfine sublevel) is efficient only for atoms with a long time-of-flight, (i.e. with a small normal velocity), thus increasing the transmission on linecenter. In the present work, we show that such a sub-Doppler signature, which is a consequence of the anisotropy of the atomic free flight, is quite general, and can even be observed in the weak-field limit as due to the transient coherent regime on a resonant two-level system.

© 1998 IEEE