Spectral lineshape analysis of four-wave mixing spectra and its application to quasi-zero-dimensional II-VI semiconductor crystallites

Abstract

Theoretical and experimental investigations are presented in order to analyze the lineshape of fourwave mixing spectra recorded by means of electronically resonant folded BOXCARS spectroscopy (special technique of CARS, coherent anti-Stokes Raman scattering). The theoretical framework presented is based on the quantum-mechanical expression of the non-linear third-order susceptibility. In order to obtain model equations those contributions of the third-order susceptibility which give rise to strong electronic resonance enhancement were exclusively used. The participation of two-photon resonances and the inhomogeneous broadening of the electronic transitions is taken into account. The theoretical background presented was applied to a semiconductor model system consisting of quasi-zero-dimensional CdS x Se 1−x nanocrystallites. The inhomogeneous broadening of this low-dimensional system is mainly caused by the size distribution of the nanocrystallites. The lineshapes of the experimentally obtained four-wave mixing spectra are well described within the theoretical framework and the homogeneous linewidth of the resonantly excited electronic state can be deduced.