An ever-increasing number of strong-field applications, such as ultrafast coherent control over matter and light, require driver light pulses that are both high power and spectrally tunable. The realization of such a source in the terahertz (THz) band has long been a formidable challenge. Here, we demonstrate, via experiment and theory, efficient production of terawatt (TW)-level THz pulses from high-intensity picosecond laser irradiation on a metal foil. It is shown that the THz spectrum can be manipulated effectively by tuning the laser pulse duration or target size. A general analytical framework for THz generation is developed, involving both the high-current electron emission and a time-varying electron sheath at the target rear, and the spectral tunability is found to stem from the change of the dominant THz generation mechanism. In addition to being an ultrabright source (brightness temperature of about ${10}^{21}\mathrm{K}$) for extreme THz science, the THz radiation presented here also enables a unique in situ laser-plasma diagnostic. Employing the THz radiation to quantify the escaping electrons and the transient sheath shows good agreement with experimental measurements.

中文翻译：

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通过相对论性激光箔相互作用向兆瓦级频谱可调谐太赫兹脉冲

越来越多的强场应用，例如对物质和光的超快速相干控制，要求驱动器光脉冲既要高功率又要在光谱上可调。在太赫兹（THz）频带中实现这样的信号源一直是一个艰巨的挑战。在这里，我们通过实验和理论证明了在金属箔上进行高强度皮秒激光辐照可有效产生兆瓦（TW）级太赫兹脉冲。结果表明，通过调节激光脉冲持续时间或目标大小，可以有效地控制THz频谱。建立了通用的太赫兹分析框架，涉及靶后方的大电流电子发射和时变电子鞘，发现光谱可调性源于主要太赫兹产生机理的变化。${10}^{21}\mathrm{ķ}$）对于极限太赫兹科学，此处介绍的太赫兹辐射还可以实现独特的原位激光等离子体诊断。利用太赫兹辐射来量化逃逸的电子和瞬态鞘，与实验测量结果显示出良好的一致性。