A self-consistent field–matter approach for pump–probe measurements in ultrafast materials

Quantitative interpretation of ultrafast pump–probe experiments requires a consistent treatment of the excitation stage, particularly under strong optical pumping where absorption saturation and interference effects become significant. We present a time-domain self-consistent framework that couples electromagnetic field propagation to semiconductor Maxwell–Bloch dynamics in thin absorbing layers. The model explicitly accounts for state filling, nonlinear absorption, and standing-wave effects without introducing phenomenological generation terms or adjustable scaling parameters. The approach is applied to low-temperature-grown GaAs layers deposited on gold mirrors, corresponding to a low-Q cavity configuration. Simulations quantitatively reproduce both the linear reflectivity oscillations as a function of layer thickness and the nonlinear saturation behavior observed experimentally. The maximum pump-induced reflectivity change is predicted from intrinsic material parameters alone. This framework provides a physically consistent basis for analyzing pump–probe measurements in multilayer absorbing structures and offers a predictive tool for the modeling and design of nonlinear semiconductor absorbers, including semiconductor saturable absorber mirrors.