Detection of the polarization spatial distribution of THz radiation generated by two-color laser filamentation

The spatial distribution of the terahertz radiation polarization is experimentally measured from a femtosecond laser two-color filament in air. Terahertz radiation generation from two-color plasma filamentation with a $\beta$-BBO crystal located behind the lens leads to the spatial inhomogeneity of the polarization distribution. Inhomogeneity of the terahertz field polarization is determined by the polarization of the fundamental harmonic of the pump radiation after passing through the $\beta$-BBO crystal. A spatial inhomogeneity of the fundamental harmonic polarization is observed owing to the $\beta$-BBO crystal acting as a phase plate illuminated by a spherical front.