Achievement

IGERT trainee Xiaofei Lu developed a new approach to directly generate elliptically polarized THz waves from laser-induced plasma with a pair of double helix electrodes. She published a paper in Physical Review Letter in March 2012 entitled “Generation of Elliptically Polarized Terahertz Waves”. She applied a helical electric field along a plasma region, then a revolving electron current was formed along the plasma and an elliptically polarized far-field terahertz wave pattern was observed. The observed THz wave polarization reveals the remarkable role of velocity retardation between optical pulses and generated THz pulses in the generation process. Extensive simulations were performed to clarify the mechanisms responsible for polarization control of air-plasma-based terahertz sources. This finding will become an essential guidance for polarization manipulation of THz waves and opens a new interdisciplinary research area within the THz community.