Scaling of the terahertz emission from liquid water lines by plasma reshaping.

Liquids are proposed to be promising terahertz (THz) sources. However, the detected THz electric field is limited by the collection efficiency and saturation effect. A simplified simulation based on the interference of ponderomotive-force-induced dipoles indicates that, by reshaping the plasma, the THz radiation is concentrated in the collection direction. Experimentally, by using a cylindrical lens pair to form a line-shaped plasma in transverse section, the THz radiation is redirected, and the pump energy dependence follows a quadratic trend, indicating that the saturation effect is significantly weakened. As a result, the detected THz energy is enhanced by a factor of ∼5. This demonstration provides a simple but effective way of further scaling detectable THz signals from liquids.