Abstract

The interaction of resonant light with atoms and molecules is one of the key problems of quantum electronics and laser spectroscopy. Coherent population trapping, heretofore realized either in closed systems [1, 2] or, very recently, in open three-level systems [3, 4], is also possible in open multilevel systems. We consider a highly degenerate rovibrational molecular transition, where the ground magnetic sublevels are coupled to the corresponding upper states, and are therefore expected to be emptied after a few lifetimes. We show that upon excitation by elliptically polarized light, the population remains trapped in a coherent superposition of ground state sublevels which does not interact further with the exciting light. Unlike the simple cases of linearly and circularly polarized light and of a closed three-level system (i.e. atoms), here the trapping level is not the one with |m| = 0, J, but rather a combination of several states, which depends on the ellipticity of the exciting light. In contrast to the population trapping in atoms, and due to the optical pumping out of the system, only ~ 1/J molecules can be trapped.

© 1996 IEEE