Wang Yadong, Das Susobhan, Iyikanat Fadil, Dai Yunyun, Li Shisheng, Guo Xiangdong, Yang Xiaoxia, Cheng Jinluo, Hu Xuerong, Ghotbi Masood, Ye Fangwei, Lipsanen Harri, Wu Shiwei, Hasan Tawfique, Gan Xuetao, Liu Kaihui, Sun Dong, Dai Qing, García de Abajo F Javier, Zhao Jianlin, Sun Zhipei
MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, and Shaanxi Key Laboratory of Optical Information Technology, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710129, China.
Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland.
ACS Photonics. 2021 Aug 18;8(8):2320-2328. doi: 10.1021/acsphotonics.1c00466. Epub 2021 Jul 13.
All-optical control of nonlinear photonic processes in nanomaterials is of significant interest from a fundamental viewpoint and with regard to applications ranging from ultrafast data processing to spectroscopy and quantum technology. However, these applications rely on a high degree of control over the nonlinear response, which still remains elusive. Here, we demonstrate giant and broadband all-optical ultrafast modulation of second-harmonic generation (SHG) in monolayer transition-metal dichalcogenides mediated by the modified excitonic oscillation strength produced upon optical pumping. We reveal a dominant role of dark excitons to enhance SHG by up to a factor of ∼386 at room temperature, 2 orders of magnitude larger than the current state-of-the-art all-optical modulation results. The amplitude and sign of the observed SHG modulation can be adjusted over a broad spectral range spanning a few electronvolts with ultrafast response down to the sub-picosecond scale via different carrier dynamics. Our results not only introduce an efficient method to study intriguing exciton dynamics, but also reveal a new mechanism involving dark excitons to regulate all-optical nonlinear photonics.
从基础研究角度以及从超快数据处理到光谱学和量子技术等一系列应用来看，纳米材料中非线性光子过程的全光控制都具有重大意义。然而，这些应用依赖于对非线性响应的高度控制，而这一点目前仍然难以实现。在此，我们展示了在单层过渡金属二卤化物中通过光泵浦产生的修饰激子振荡强度介导的二次谐波产生（SHG）的巨大且宽带全光超快调制。我们揭示了暗激子在室温下增强SHG的主导作用，增强倍数高达约386倍，比当前最先进的全光调制结果大2个数量级。通过不同的载流子动力学，在跨越几个电子伏特的宽光谱范围内，可以在亚皮秒尺度的超快响应下调整所观察到的SHG调制的幅度和符号。我们的结果不仅引入了一种研究有趣激子动力学的有效方法，还揭示了一种涉及暗激子来调控全光非线性光子学的新机制。
