Simulating Nonlinear Optical Signals from Ultrafast Transient Polarization Spectroscopy in Excited State Molecules: An Experimentalist's Approach

Ultrafast Transient Polarization Spectroscopy is a nonlinear spectroscopic method that is able to measure excited state nonlinear optical signals as a function of time delay between the incident pulses. In this technique, an excitation pulse first excites a population of target molecules to an excited state and a pair of probing pulses use the optical Kerr effect to sample the transient nonlinear optical susceptability of the excited system. These signals are often difficult to interpret due to the nonlinear nature of signal generation and a lack of theoretical treatment for these experiments. Here we present a flexible approach to simulating experimentally measurable nonlinear excited state signals by treating the case of an N-level molecular system using a Liouville Space framework in the time domain. Applications of this method to aid in the analysis of recently collected data on optically excited nitrobenzene are also explored.