Cai Jiahua, Chen Sai, Geng Chunyan, Li Jianghao, Quan Baogang, Wu Xiaojun
School of Electronic and Information Engineering, Beihang University, Beijing 100191, China.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Nanophotonics. 2023 Feb 15;12(13):2517-2526. doi: 10.1515/nanoph-2022-0766. eCollection 2023 Jun.
Strong-field terahertz (THz)-matter interaction permits the investigation of nonequilibrium behaviors in the nonperturbative zone. However, the unavailability of a high-field free-space THz source with high repetition rates, excellent beam quality, and high stability hinders its development. In this work, we obtain the nonlinear modulation dynamics of a "THz-nano" metasurface on silicon substrates using a time-resolved strong-field THz-pump THz-probe (TPTP) with a thousand orders local field enhancement through confining THz waves into nano-gaps (15 nm, /33,000). By switching the THz field strength, we successfully realize a self-modulation ∼50 GHz frequency shift, which is further verified via the TPTP ultrafast time-resolution technique. The phenomenon is attributed to the impact ionization (IMI) of the silicon substrate under the excitation of extremely confined strong THz fields in nano-gaps. Both strong-field induced intervalley scattering (IVS) and IMI effects of photodoped silicon occurring in nano-gaps and large-area substrates were also observed by 800 nm optical injection of carriers. These aforementioned findings provide a robust research platform for the realization of ultrafast time resolution nanoscale strong-field THz-matter interaction and new ideas for nonextreme laboratories to realize extreme THz science, applications, and THz nonlinear modulation device development.
强场太赫兹（THz）与物质的相互作用使得在非微扰区域研究非平衡行为成为可能。然而，缺乏具有高重复率、优异光束质量和高稳定性的高场自由空间太赫兹源阻碍了其发展。在这项工作中，我们使用时间分辨强场太赫兹泵浦太赫兹探测（TPTP）技术，通过将太赫兹波限制在纳米间隙（15纳米，/33,000）中，获得了硅基衬底上“太赫兹-纳米”超表面的非线性调制动力学，该技术具有千倍的局域场增强。通过切换太赫兹场强，我们成功实现了约50吉赫兹的自调制频率偏移，这通过TPTP超快时间分辨技术得到了进一步验证。该现象归因于在纳米间隙中极强的受限强太赫兹场激发下硅基衬底的碰撞电离（IMI）。通过800纳米光注入载流子，还观察到了在纳米间隙和大面积衬底中发生的光掺杂硅的强场诱导谷间散射（IVS）和IMI效应。上述发现为实现超快时间分辨纳米尺度强场太赫兹与物质相互作用提供了一个强大的研究平台，并为非极端实验室实现极端太赫兹科学、应用及太赫兹非线性调制器件开发提供了新思路。
