Classical Approach To Off-Resonant Raman Coherence With Chirped Femtosecond Laser Pulses

Raman coherence of electronically off-resonant transitions provides a simple class of Raman techniques that, when realized with chirped femtosecond laser pulses, are commonly studied with reference to the methods of quantum mechanics. In this work, we show instead that the classical approach, when extended to chirp-dependent laser fields, is equally effective in reproducing experimental results that are particularly sensitive to the chirp carried by the laser pulses. The extension is nothing but a follow-up of the traditional model based on the driven damped harmonic oscillator, which is however known to work for transform-limited femtosecond pulses. The demonstration starts with the comparison of the time-dependent third-order polarizations for the Liouville-space wavepacket representation with the classical analog. The formal similarity between these nonlinear polarizations is further analyzed in the frequency domain to show an important difference related to the handling of the phase factor containing the carrier frequencies of the laser pulses. Finally, we simulate a couple of significant and acknowledged chirp-dependent experimental measurements in the impulsive regime of stimulated Raman scattering.