Lez #33+34 Diagrams for 3rd order processes: pump-probe and stimulated Raman

We re-discussed the pump probe response (stimulated emission (SE), bleaching and excited state absorption (ESA)) commenting on the differences between bleaching and SE. 

We then 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.