Intense multicycle THz pulses generated by laser-produced nanoplasmas

We present a novel scheme to obtain robust, narrowband, and tunable THz emission by using a nano-dimensional overdense plasma target that is irradiated by two counter-propagating detuned laser pulses. So far, no narrowband THz sources with a field strength of GV/m-level have been reported from laser-solid interaction. We report intense THz pulses at beat-frequency ($\simeq$30THz) generated due to strong plasma current produced by the beat ponderomotive force in the colliding region, with an unprecedentedly high peak field strength of 11.9GV/m and spectral width $(\mathrm{\Delta }f\mathrm{/}f$$\simeq$$5.3\mathrm{\%})$ from 2D PIC simulations. Such an extremely bright narrowband THz source is suitable for various ambitious applications.