Backward degenerate four-wave mixing

Measurements of x(3>(—cu to, to, —to) by backward-wave degenerate four-wave mixing (DFWM). Two pump beams of equal intensity A, and l2 and opposite phase meet at the sample and, with a weaker probe beam /3, cause the formation of an emitted beam /4. M1, M2, M3 and M4 are mirrors BS1, BS2, and BS3 are beam splitters. 

FIGURE 49.7. Schematics of experimental arrangement of the degenerate four-wave mixing (backward geometry) experiment. 

Fig. 13. Schematic for backward scattered (phase conjugate) degenerate four-wave mixing. (BS = beam splitter, M = mirror.) The pump beams (1) and (2) are collinear and counterpropagating. The probe beam (3) when incident on the sample leads to the creation of the phase conjugate beam (4), which is detected and compared to a suitable reference. The delay lines are included so that the timing of pulsed light arriving at the sample via paths (1), (2), and (3) can be varied.

---