| Summary: | Abstract We present a novel scheme to obtain robust, narrowband, and tunable THz emission using a nano-dimensional overdense plasma target, 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 (mostly half-or single-cycle THz pulses with only broadband frequency spectrum). From two- and three-dimensional particle-in-cell simulations, we find that the strong plasma current generated by the beat ponderomotive force in the colliding region, produces beat-frequency radiation in the THz range. Here we report intense THz pulses $$(f\simeq 30 \;$$ ( f ≃ 30 THz) with an unprecedentedly high peak field strength of 11.9 GV/m and spectral width $$(\Delta f/f\simeq 5.3\%)$$ ( Δ f / f ≃ 5.3 % ) , which leads to a regime of an extremely bright narrowband THz source of TW/cm $$^{2}$$ 2 , suitable for various ambitious applications.
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