Elliptically polarized Terahertz emission from a femtosecond laser filament in air

摘要

We diagnosed the polarization characteristics of Terahertz (THz) emission from a femtosecond laser filament in air in theforward direction by using a wire grid polarizer and E-O sampling technique. The experimental results havedemonstrated that the investigated THz pulse is elliptical polarized. It indicates that there is a new generation mechanismfor THz emission from a laser filament other than the transition-Cherenkov radiation which is radially polarized. Thegeneration mechanism could be through four-wave optical rectification or second-order optical rectification inside thefilament due to the spatial asymmetry of the generated plasma column in the experiment.