Femtosecond two-beam coupling energy transfer from Raman and electronic nonlinearities

We present a study of two-beam coupling energy transfer arising from electronic and nuclear (i.e., Raman) contributions to the third-order refractive nonlinearity. Calculations of transient two-beam coupling in fused silica with no free parameters agree reasonably well with experiments. Numerical calculations of two-beam coupling in a medium with a purely electronic nonlinearity modeled by a Debye-type response are presented. The calculations indicate that it should be possible, although challenging, to measure electronic two-beam coupling for response times as short as similar to 0.1 fs. Experiments designed to isolate the electronic response fail to produce two-beam coupling signals but do indicate that the time scale of the electronic response is well below ifs. (C) 2000 Optical Society of America [S0740-3224(00)02109-3].