Thesis defense of Laura Krauß-Kodytek

The two-photon absorption is a nonlinear optical process with various properties which makes it an excellent basis for a wide range of different applications. In this thesis the non-degenerate two-photon absorption coeffi‑cient β (ħω1, ħω2) as a function of the frequency ratio ω1/ω2 of the two driving fields is experimentally investigated whereby the sum energy ħω1+ħω2 is kept constant. The studied materials are the prototypical semiconductors ZnSe, GaAs and Si. Regardless of the direct or indirect character of the bandgap, the two-photon absorption strength increases with increasing ratio ω1/ω2 ≥1. The experimental data of ZnSe and GaAs agrees well with corresponding theoretical predictions for direct semiconductors. Si shows overall smaller absorption strengths. These results also agree with theoretical predictions for indirect semiconductors. In addition, different crystallographic orientations of the samples and polarization configurations of the two driving fields are analyzed. These results make an important contribution to the so far rarely investigated orientation and polarization anisotropy of the non-degenerate two-photon absorption.

 

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