Raman amplification of coherent Stokes wave at biharmonic laser pumping of single-mode silica fibers

Abstract

We have studied a nonlinear process in the generation of narrow-band tunable Stokes radiation of frequency v s=2 v 2− v 1 under a biharmonic tunable pulsed laser pumped with v 1 and v 2 frequencies ( v 1 > v 2) in single-mode silica fibers. The Stokes radiation is generated at a high conversion efficiency up to 40% when the pumping frequency difference is v 1 − v 2<1200 cm −1 which corresponds to the region of vibronic resonances of fused silica, while its power is decreased by several orders at 1200 cm −1 < v 1− v 2<3000 cm −1. The process is explained by Raman amplification of the coherent probe Stokes wave which is generated by the four-photon mixing.