Spectral dependence of the depolarization ratio of pure water

Spectral variation of the depolarization ratio (δ) of water in the visible domain is largely unknown. Prior studies, all of which were conducted before 1970, show contradicting trends. We measured δ of pure water at three wavelengths using a photon counting scattering device, the LS spectrometer. Our measured values for δ average0.0417±0.01369 for 491 nm, 0.0393±0.00800 for 532 nm, and 0.0363±0.00494 for 660 nm. While this observed trend of slightly increasing values with decreasing wavelength falls somewhat within the measurement uncertainty, it is consistent with theory. As the frequency of light increases in the visible domain, the polarizability of water molecules also increases. However, the anisotropic part of polarizability increases in relatively greater amounts than the increase in the isotropic part of polarizability, which results in increasing δ with decreasing wavelength.