Subnatural linewidths in two-photon excited-state spectroscopy.

Department of Physics, Durham University, Rochester Building, South Road, Durham DH1 3LE, UKWe investigate, theoretically and experimentally, absorption on an excited-state atomic transi-tion in a thermal vapor where the lower state is coherently pumped. We nd that the transitionlinewidth can be sub-natural, i.e. less than the combined linewidth of the lower and upper state.For the speci c case of the 6P