Time-ordered diagrams, molecular photonics

Figure 2. The three time-ordered diagrams representing second harmonic generation. Pump photons of wave vector k and polarization X impinge on the molecule from the left and the subsequent harmonic (k, leaves the molecular world line from the right. We assume the initial and final state of the molecule is the ground state 0 the intermediate states are labelled r and s.

Figure 16. The time-ordered diagrams associated with the formation of an appropriate molecular grating for SHG. The two writing beams r2 and r3 populate the upper electronic state via two- and single-photon absorption respectively.

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