Numerical Liouville approach: Three-type analysis of virtual excitation processes of third-order nonlinear optical spectra in third-harmonic generation

Abstract

An analysis method based on virtual excitation processes is developed in numerical Liouville approach, which is a new nonperturbative method presented before. In this analysis method (NLA three-type analysis method), third-order nonlinear optical susceptibilities χ(3)g(ω) obtained by the NLA method can be divided into the three-type virtual excitation processes similar to the three-type analysis based on the time-dependent perturbation theory (TDPT three-type analysis). The NLA three-type analysis method is superior to the TDPT three-type analysis one in the points as follows: (1) the NLA three-type analysis can treat the phenomena caused by the intensity-dependent nonlinear susceptibilities including nonperturbative effects and (2) the NLA three-type analysis can divide the resonant nonlinear susceptibilities into three types of virtual excitation processes. In order to explain the procedure of the present analysis, we try to elucidate the characteristics of virtual excitation processes of nonlinear optical spectra in THG for a three-state model that mimics the electronic excited states of a system with noncentrosymmetric charge distribution.