Nonlinear Modelling Of Ultrafast Free-Electron Dynamics and Transient Reflectivity in Water-Like Media under Femtosecond Laser Excitation

Ultrafast laser excitation of transparent dielectric media initiates a sequence of electronic processes that determine the early stages of energy deposition and the resulting optical response. We investigate the generation and temporal evolution of free carriers in water-like dielectric media irradiated by femtosecond laser pulses. The carrier dynamics are described within a nonlinear rate-equation framework, while the resulting time-dependent electron density is used to evaluate the transient optical response through a Drude-type dielectric function and Fresnel relations. The analysis reveals a pronounced wavelength dependence of the carrier generation efficiency arising from the variation of the multiphoton excitation order across the considered spectral range. We have shown that wavelength-dependent nonlinear excitation governs both the buildup of free carriers and the resulting ultrafast optical response, providing a consistent framework for interpreting pump-probe reflectivity measurements in water-like dielectric systems.