Ultrafast strong‐field terahertz nonlinear nanometasurfaces
Jiahua Cai, Sai Chen, Chunyan Geng, Jianghao Li, Baogang Quan, Xiaojun Wu
Abstract
Abstract 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, λ /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.