Abstract

The suppression of forward propagating Stimulated Hyper-Raman (SHR) emission is well-studied in sodium vapor.^[1] SHR emission is the result of a two-photon excitation near, but not directly to, an allowed transition, and a subsequent one-photon transition. It propagates parallel or antiparallel to the laser photons. The theory predicts that SHR emission to a state linked to the ground state by a one-photon transition a suppressed by an interference with a Parametric Four-Wave Mixing (PFWM) emission that links that state to the ground state. Using perturbation techniques to solve the Maxwell-Bloch equations, it was found that the SHR and PFWM emissions are of equal magnitude and opposite phase. Since PFWM emission only propagates in the forward direction due to phase-matching considerations, only the forward SHR emission is canceled. This was demonstrated experimentally in sodium. An untested corollary of this theory is that no suppression occurs if the state is not linked to the ground by a one-photon transition.

© 1992 IQEC