Figure 2.

Pump–probe modalities associated with the SRS process. (a) SRS process involves energy transfer from the pump field to the Stokes field via excitation of molecular vibration. (b) Cross-phase modulation: the pump beam (ω_p) changes the nonlinear refractive index at the focus through optical Kerr effect, thus affecting the probe beam (ω_pr) propagation and frequency. (c) Transient absorption: a pump–probe process that involves excitation of electronic energy levels. (d) Thermal lensing effect: the change of refractive index at the focus induced by the local heating after absorption of the pump photons, affecting the propagation of the probe beam.