Modeling Terahertz radiation from laser-induced Micro-plasmas
Résumé
Several applications in spectroscopy and sensing require sources in the terahertz (THz) domain. Among others, gases are promising media for generation of THz radiation by the interaction with ionizing intense laser pulses, as has already been established by various theoretical and experimental works. In particular, THz emission from laser-induced micro-plasmas was demonstrated recently: A femtosecond-laser beam is focused strongly into a gas that is ionized within the focal region resulting in a small plasma. The interaction of the same laser with the
plasma leads to generation of non-linear radiation as THz and second harmonic (SH) radiation. Multiple mechanisms responsible for the THz emission are proposed in the literature. We present an approach describing two of the mostly discussed mechanisms in a consistent manner. The properties of the THz radiation are considered for single- and twocolor laser pulses: Spectral properties, radiation profiles and conversion efficiencies are presented. The results of the model are benchmarked by rigorous particle-in-cell (PIC) simulations accounting for full kinetics of the charged particles as well as for ionization and collisions.