Diagrammatic Representation of the 3rd-order Polarization In Transient Cars

A diagrammatic perturbative approach is adopted to derive the expression for the third-order polarization, P(3) which originates the anti-Stokes emission in a time-resolved CARS experiment. The various contributions to P(3) are calculated assuming that laser fields are off-resonance with respect to any electronic level of material system. The resonant part of the polarization consists of two terms, in which the roles of pump and probe pulses at frequency omega-1 are exchanged. The global expression allows the direct calculation of the signal time profile in a transient CARS experiment once a model is assumed for the laser pulse shape.