Self-compression of a femtosecond pulse due to Raman coherence of molecular rotations

The phenomena of self-modulation and self-compression of a femtosecond laser pulse due to a Raman-active medium of hydrogen, were investigated. It was observed that femtosecond pulses produce the Stokes emissions of ortho-hydrogen and para-hydrogen, depending on the input beam conditions. The shape of the output pulses was found to drastically change as a function of the Stoke emission intensity and total width of the spectrum. The results show that this was attributed to nonlinear modulation of the wave form, which was induced by coherent rotational motions of hydrogen molecules in the time domain.