Towards compact efficient fs-laser-induced THz sources from microplasmas

Terahertz (THz) sources are indispensable for various applications such as THz time-domain spectroscopy. A promising approach to generate broadband THz radiation is to employ laser-induced gas plasmas, which has already been demonstrated for various settings [1, 2]. In order to miniaturize such sources, it has been proposed to exploit single-color laser-induced microplasmas [3]. Then, a conical THz emission is produced by longitudinal low-frequency currents driven by the ponderomotive force. However, the laser-to-THz conversion efficiency for this scenario has been shown to saturate for higher pulse energies to approximately 10^-6 [4]. In order to increase the efficiency, we investigate theoretically [4] the ionization current mechanism driven by two-color laser pulses [2] for microplasmas.