Unveiling of control on the polarization of supercontinuum spectra based on ultrafast birefringence induced by filamentation

Abstract

An intensity pump femtosecond (fs) pulse incident into a transparent medium will produce filamentation and accompany supercontinuum (SC) spectrum generation. The polarization of the SC spectrum is always parallel to that of the pump pulse. How to control the polarization of the SC spectrum is a very interesting and crucial issue due to its great potential applications in remote sensing and time-resolved spectroscopy. Here we present a method to control the polarization of the SC spectrum generated in an optical isotropic medium, based on the nonlinear interaction between the two pump pulses with different linear polarizations. During the fs pulse filamentation, the optical Kerr effect induces ultrafast birefringence in the optical isotropic medium, which leads to different refractive indices in the two orthogonal directions parallel and perpendicular to the incident polarization, and hence, the resulting relative phase difference changes the polarizations of the pump pulses. The polarization states of both the pump pulses and the SC spectra can be achieved by changing the angle between the polarization directions of the two pulses. We unveil the mechanism of the polarization changes of the pump pulses and the SC spectra.