In the amplitude and phase-resolved laser experiments, the s-polarized 1030 nm output from an amplifier laser system (10 W Pharos, Light Conversion, 200 fs, 200 kHz) is attenuated to 40 mW at the sample, directed onto the silica:water interface using a 100 mm focusing lens while ultrapure water equilibrated in laboratory air overnight (<2 µS cm -1 ) is flowed through the cell at a rate of 2 mL min -1 (Fig. ). A peristaltic pump is used to control the flow rate. A 100 mm offaxis parabolic mirror directs the fundamental and the SHG signal from the interface onto a set of optics for time and spatial overlap, and into a photon counter after passing through a short pass filter and a 520 nm bandpass (FWHM=40 nm) filter, as described earlier. Nonlinear optical interference fringes are recorded using a 50 µm thin quartz wafer on a 100 mm motorized translational stage as a local oscillator source from which the SHG amplitude and phase are determined as detailed in our prior work. After recording a test fringe to ensure accurate alignment, system is allowed to equilibrate for at least 2 hours while ultrapure water continuously flows through the cell at a rate of 2 mL min -1 , after which the SHG phase and amplitude are stable.