Assessing the dephasing dynamics of water from linear field-resolved pulse propagation experiments and simulations in highly absorbing solutions

We measure and simulate electric field distortions resulting from propagation of mid-infrared pulses that are resonant with the OH stretch vibration through optically dense HDO:D2O. These distortions are characterized experimentally by full-field-resolved time- and frequency-domain measurements, specifically cross-correlation frequency-resolved optical gating and spectral interferometry, establishing amplitude and phase of the signal fields. Correlation-function finite-difference time-domain (CF-FDTD) simulations using response functions for the OH-stretching vibration, obtained from nonlinear spectroscopic studies reported by others, show that details of the line shape functions are manifested in the measured (linear-response) spectrograms. The degree of homogeneous or inhomogeneous broadening present in the various model correlation functions is readily apparent in the measured and simulated signals. Surprisingly, the published correlation functions are shown to range from modest inhomogeneous to homogeneous line broadening. The present experimental and simulation approach is very useful for establishing the correct form of energy gap correlation functions and dephasing dynamics of IR and optical transitions. In the case of HDO:D2O, correlation functions with modest inhomogeneous broadening better reflect our measured responses.