Influence of cutting off position of plasma filament formed by two-color femtosecond laser on terahertz generation**Project supported by the National Defense Basic Scientific Research Program of China (Grant No. Z202013T001) and Postgraduate Innovation Fund Project by Southwest University of Science and Technology, China (Grant No. 16ycx104).

Abstract

Femtosecond laser filamentation is a method of generating terahertz, which has wide application in terahertz sub-wavelength resolution imaging. In this paper, the plasma filament formed by femtosecond laser focusing was terminated with an alumina ceramics at different positions and the influence of the cutting off position of the plasma filament on the terahertz wave was studied. The results showed that the terahertz amplitude increases as the position approaches the end of the filament gradually. The stability of amplitude and peak frequency of the terahertz generated by the filament formed by two-color femtosecond laser via a lens with a longer focal length is lower than that through a lens with a shorter focal length, especially the terahertz amplitude at the end of the filament. The study will be helpful for future researchers in the field of THz sub-wavelength imaging utilizing femtosecond laser filament.