Within the density matrix framework, we obtained an expression for the transient third-order susceptibility and relating refractive index induced by stimulated Raman scattering of femtosecond pulse on molecular rotational transitions. It is explicitly shown that the nuclear sub-system response to the pulse field is anisotropic and delayed in time. Calculated average values of the refractive index n2 for molecular nitrogen (2°10-19 cm2/W) and oxygen (4°10-19 cm2/W) agree with those available in literature.
femtosecond pulses, nonresonant interaction, molecules
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