Radiation Dynamics and Manipulation of Extreme Terahertz Surface Wave on a Metal Wire

Recent reports on sub-terahertz (THz) generation from a laser-irradiated wire might have evaded the most essential contents of the wire radiation dynamics. Here, the origin of terahertz generation from a metal wire is revisited and a comprehensive diagnosis of the terahertz radiation from a 100 µm-diameter tungsten wire irradiated by an intense femtosecond laser is implemented. For the first time, the long-neglected but more efficient high-frequency terahertz radiation is experimentally observed of which the spectra, polarization, tunability, and wire-length-dependent intensification are investigated comprehensively. A new picture of the wire radiation dynamics is presented to reveal the origin of the extreme terahertz surface wave, its evolution, and radiation mechanism. This extremely intense and ultrashort half-cycle surface wave is spontaneously induced by a laser-driven transient charge-separation field and evolves into a multi-cycle surface wakefield structure as it propagates along the wire owing to the self-interaction between the surface wave and its carrier, the surface current. By manipulating the coupling and transport dynamics of the surface wave on the wire, tunable and intensified THz radiation covering a wide range from 0.1 to 20 THz has been realized, paving the way for broad applications such as terahertz acceleration, bio-medicine, nonlinear THz science and beyond.