双焦点级联等离子体中的强度起伏和带宽扩展太赫兹辐射
Intensity-surged and Bandwidth-extended Terahertz Radiation in Two-foci Cascading Plasmas
摘要：
气体介质中的双色强场混频是产生明亮宽带太赫兹辐射的一种常用方法。在这里，我们提出了一种新的和违反直觉的方法，以提高太赫兹性能的双色方案。除了我们所知的最大THz产生发生在双色焦点重叠的情况下之外，我们发现，当双色光束的焦点沿传播轴明显分离时，导致级联等离子体，THz转换效率激增一个数量级，带宽扩展超过2倍，在800/400 nm、$\sim$ 35 fs驱动激光器的条件下，实现了$10^{-3}$转换效率和$>$ 100 THz带宽。借助于脉冲传播方程和光电流模型，我们可以部分地理解级联等离子体中激光能量的空间再分布导致的太赫兹产生和吸收之间的折衷。该方法可以推广到中红外驱动激光器，并有望在太赫兹峰值功率和转换效率方面创造新的纪录。
英文摘要：
The two-color strong-field mixing in gas medium is a widely-used approach to generate bright broadband terahertz (THz) radiation. Here, we present a new and counterintuitive method to promote THz performance in two-color scheme. Beyond our knowledge that the maximum THz generation occurs with two-color foci overlapped, we found that, when the foci of two-color beams are noticeably separated along the propagation axis resulting in cascading plasmas, the THz conversion efficiency is surged by one order of magnitude and the bandwidth is stretched by more than 2 times, achieving $10^{-3}$ conversion efficiency and $>$100 THz bandwidth under the condition of 800/400 nm, $\sim$35 fs driving lasers. With the help of the pulse propagation equation and photocurrent model, the observations can be partially understood by the compromise between THz generation and absorption due to the spatial redistribution of laser energy in cascading plasmas. Present method can be extended to mid-infrared driving laser, and the new records of THz peak power and conversion efficiency are expected.
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