Interferometric four-wave-mixing experiments on ZnSe quantum-well structures

We report interferometric four-wave-mixing (FWM) experiments on ZnSe quantum-well (QW) structures. By varying the phase relation of two phase-locked pulses in direction k 1 (interferometric pulses) and using an additional pulse with wave vector k 2 we observe an oscillating FWM signal in the direction 2k 2 - k 1 . This technique is specially suitable to investigate the influence of effects beyond third order with respect to the optical field, since these effects manifest themselves as higher integer harmonics in the observed FWM trace. We found a maximum influence of higher harmonics for overlapping interferometric pulses and for a delay time of roughly 1 ps of the third pulse. The experimental results are well reproduced by optical Bloch equations combined with a phenomenological density-dependent dephasing.