  We demonstrate rapid imaging based on four-wave mixing (FWM) by assessing the
quality of advanced materials through measurement of their nonlinear response,
exciton dephasing, and exciton lifetimes. We use a WSe$_2$ monolayer grown by
chemical vapor deposition as a canonical example to demonstrate these
capabilities. By comparison, we show that extracting material parameters such
as FWM intensity, dephasing times, excited state lifetimes, and distribution of
dark/localized states allows for a more accurate assessment of the quality of a
sample than current prevalent techniques, including white light microscopy and
linear micro-reflectance spectroscopy. We further discuss future improvements
of the ultrafast FWM techniques by modeling the robustness of exponential decay
fits to different spacing of the sampling points. Employing ultrafast nonlinear
imaging in real-time at room temperature bears the potential for rapid in-situ
sample characterization of advanced materials and beyond.
