Generation of elliptically polarized terahertz radiation from a water column

Elliptically or circularly polarized terahertz (THz) radiation plays a crucial role in advanced applications such as chiral spectroscopy, spintronics, and polarization-sensitive imaging and communication. Here, we demonstrate an efficient method for generating elliptically polarized THz radiation from a single-color laser-driven water column. By tilting the water column along the laser propagation direction and displacing the laser axis from the column center, both vertical and horizontal THz components are produced with a nonzero relative phase. As a result, elliptically polarized THz radiation with an ellipticity up to 0.75±0.02 is achieved in our experiment. Furthermore, the ellipticity and handedness of the emitted THz waves can be flexibly controlled by adjusting the tilt angle and the horizontal offset of the water column. This work provides a simple and robust scheme for controllable generation of elliptically polarized THz radiation, opening new opportunities for THz-based spectroscopy, imaging, and information technologies.