Highly efficient frequency conversion in double lambda systems without maximal atomic coherence
by
Arlene D. Wilson-Gordon
Bar-Ilan University, Israel
Coauthors: Hagay Shpaisman (Bar-Ilan University), Harry Friedmann (Bar-Ilan University)

The irrelevance of phase matching in obtaining efficient four-wave mixing (FWM) in various systems has recently been stressed. For example, it has been demonstrated that efficient frequency conversion can be achieved in a double lambda system within the coherence length, by establishing electromagnetically induced transparency (EIT), via maximal Raman coherence. We have re-examined this claim and found that the propagation distance for efficient conversion can also be shortened by increasing the intensity of the generating beams. We have therefore implemented an alternative scheme, based on the transverse intensity profile control of the parametrically interacting fields by means of ordinary (one-photon) or Raman self-focusing and cross-focusing. We find that in the presence of such focusing, the on-axis intensity of the generated field is much higher than in the absence of focusing, provided the two-photon coherence is not maximal. Our results clearly indicate that saturation can replace EIT for avoiding losses by absorption, and that the implementation of sufficiently intense applied fields is a sufficient condition for making phase matching irrelevant and for obtaining efficient frequency conversion within the coherence length.

Date received: April 1, 2004