Terawatt-level widely-tunable terahertz pulses from femtosecond laser-irradiated metallic foils

High-power tunable terahertz (THz) sources are highly desired for numerous applications. However, such sources with wide spectral tunability remain very lacking. Here we report on the highly efficient production of terawatt (TW)-level widely-tunable THz pulses, experimentally by harnessing the high-contrast sub-petawatt femtosecond laser impinging onto metallic foils. THz energy and autocorrelation measurements reveal the scaling-up of THz yield and the ultrabroadband tunability of THz spectra with the foil thickness. The THz peak power reaches up to ∼2TW with the laser-to-THz energy conversion efficiency of ∼1%, and the THz center frequency is tunable across 3∼20THz. Theoretical modeling together with measurements of escaping electrons explains the observed THz results, and attributes the THz spectral tunability to the controlled spatiotemporal dynamics of laser-accelerated energetic electrons with varying foil thickness. Single-shot THz-induced ionization damage of fused silica is presented as a proof-of-concept illustration of the ultrahigh THz intensity available. To the best of our knowledge, our results demonstrate a record-strong THz source spectrally-tunable across 3∼20THz—a spectral region where the generation of intense sources has long been a formidable challenge before. Such an extreme THz source will not only open up avenues for the far-beyond-equilibrium control over matter, but also unlock the previously inaccessible relativistic THz optics.