Interferometrie Four-Wave-Mixing Spectroscopy on Semiconductors

In ultrafast nonlinear spectroscopy interferometric techniques can be applied both for heterodyne detection of the signal and for the excitation of the sample by phase-locked pulses, thus delivering coherent control [1] over the system. Such techniques have been predicted to be extremely sensitive with respect to the dynamics of elementary excitation [2] and have been applied to the study of non-Markovian dynamics of molecules [3, 4]. For the case of semiconductors, interferometric sensitivity has been employed for detection purposes [5] and the use of phase-locked pulses has been reported quite recently [6]. In this paper we report the observation of a novel interference phenomenon in interferometric four-wave-mixing due to contributions beyond the third order perturbational limit. An analysis of the observed interferences allows for an estimation of the importance of these higher order contributions.