Mechanism of depolarization of white light generated by femtosecond laser pulse in water

The polarization state of the white light produced by a femtosecond laser pulse through a water cell is investigated. The depolarization of the white light was found to be induced by magnification of the polarization perturbation in the incident light which is caused by the focus lens. Cross-phase modulation (XPM) of the third order nonlinear polarization is proposed as the depolarization mechanism.