Momentum conservation in Raman-induced optical Kerr effect

In the nonlinear interaction of femtosecond (fs) laser pulses with some simple molecular liquids we have observed and proved vibrational quantum interference (VQI) in the accompanying Raman processes. An analysis is given in this report of the associated momentum conservation. In addition to the propagation directions of the attending electromagnetic waves, the dispersion of the refractive indices around the vibrational resonances is invoked. The analysis leads to a prediction of active normal vibrations as well as the experimental condition for observing the VQI.