Two-photon excitation via quantum interference

Summary form only given. It has been shown that two-photon absorption can be controlled by quantum interference in the multiple excitation paths created by a coupling field. Recently, Harris and Yamamoto (1998) described a four-level system that utilizes electromagnetically induced transparency (EIT) to switch on and off the two-photon excitation. Because the cancellation of the one-photon excitation, the enhanced two-photon excitation may be observable under very low light intensities. We have carried out an experimental study of two-photon excitation via quantum interference in multi-level Rb atomic systems based on the D/sub 1/ and D/sub 2/ transitions. The Rb systems can be viewed as quasi-four level systems. The experiments were done in an /sup 87/Rb isotope vapor cell.