Ultrafast formation of hydrated electrons in water at high concentration: Experimental evidence of the free electron

Using a time-resolved optical interferometric technique, we investigate the ultrafast primary events following the interaction of an ultrashort laser pulse with pure water in the TW/cm² regime. Because our method is sensitive to the quasi-instantaneous electron energy level position, we demonstrate that in contrast to the well-known low-intensity regime, where the free electrons are instantaneously captured by preexisting traps, in this new regime of excitation, free electrons are clearly observed, exhibiting a substantial contribution in the near IR. The delayed localization is attributed to the saturation of pre-existing cavities in the liquid by the large number of the excited electron states created.