Using high-resolution, two-dimensional particle-in-cell simulations, we investigate numerically the mechanisms of terahertz (THz) emissions in submicron-thick carbon solid foils driven by ultraintense ($\sim 10^{20}\,\rm W\,cm^{-2}$), ultrashort ($30\,\rm fs$) laser pulses at normal incidence. The considered range of target thicknesses extends down to the relativistic transparency regime that is known to optimize ion acceleration by femtosecond laser pulses. By disentangling the fields emitted by longitudinal and transverse currents, our analysis reveals that, within the first picosecond after the interaction, THz emission occurs in bursts as a result of coherent transition radiation by the recirculating hot electrons and antenna-type emission by the shielding electron currents traveling along the fast-expanding target surfaces.

中文翻译：

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超强飞秒激光脉冲辐照亚微米固体目标的太赫兹发射

我们使用高分辨率、二维的细胞内粒子模拟，数值研究了由超强 ($\sim 10^{20}\,\rm W) 驱动的亚微米厚碳固体箔中太赫兹 (THz) 发射的机制\,cm^{-2}$), 超短 ($30\,\rm fs$) 激光脉冲在法向入射。所考虑的目标厚度范围向下延伸到相对论透明区域，该区域已知通过飞秒激光脉冲优化离子加速。通过解开纵向和横向电流发射的场，我们的分析表明，在相互作用后的第一个皮秒内，由于再循环热电子的相干跃迁辐射和屏蔽电子的天线型发射，太赫兹发射爆发沿着快速膨胀的目标表面流动的电流。