Lez #29+30 Double sided Feynman diagrams: Stimulated Raman

 We derived the double sided Feynman diagrams associated with stimulated Raman processes, i.e. for a three level systems (2 electronic states, with the ground state having 2 vibrational levels) in presence of two different pulses, namely the Raman pulse and the Stokes pulse, detecting the heterodyne response arising on top of the stokes beam.

Lez #27+28 Double sided Feynman diagrams: Transient absorption

We evaluated the third order non linear response in the pump probe scheme. Two beams are used to accomplish the 3 interacitons, excluding two photon processes and using RWA the number of fiagrams is reduced to 6, corresponding to 3 different processes: excited state absorption, stimulated emission, ground state bleaching. Bleaching and stimulated response give the same response, unless the system is evolving onto the excited state, for example due to vibrational relaxation.

Lez #25+26 Double sided Feynman diagrams: linear absorption

 We introduced the double sided Feynman diagrams to describe the perturbative expansion of the polarization, end explicitly evaluated the linear absorption of a two level system.