Dynamics of optical polarizability of liquid water exposed to intense laser light

Variations in the optical properties of pure water induced by a femtosecond laser (wavelength 800 nm, intensity $ \sim {10^{12}}\;{\rm W}/{{\rm cm}^2} $∼10^12W/cm^2) were studied by a pump–probe interferometric technique. Laser photoionization was shown to increase both the refractive index and absorbance of the water. While the absorption dynamics were found to be in a good agreement with previous studies, the temporal behavior of the refractive index exhibited novel features. It was found that the always-positive refractive index contains distinct peaks at the beginning and end of the laser pulses. This behavior was attributed to the Kerr effect in water molecules and in wet/hydrated electrons produced by photoionization, respectively.