Phase matching, DFWM

DFWM Laser-induced grating Beam of light at ft>4 = =0)2 = 0)z Very sensitive, no phase matching Multiple mechanisms (local and nonlocal), not a Raman technique... 

As seen, the term scheme for DFWM is especially simple all four photons induce transitions between real states. This "resonance enhancement" results in a higher signal strength as compared with, for example, CARS. Momentum conservation determines the direction of fhe resulting signal wave. Since the phase-matching condition is (for the notation see Fig. 6.13) ... 

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