Division of Physics and Applied Physics, School of Physical and Mathematical Sciences , Nanyang Technological University , Singapore 637371.
Department of Electrical and Computer Engineering , Johns Hopkins University , Baltimore , Maryland 21218 , United States.
Nano Lett. 2018 Mar 14;18(3):1686-1692. doi: 10.1021/acs.nanolett.7b04707. Epub 2018 Feb 6.
Modulating second harmonic generation (SHG) by a static electric field through either electric-field-induced SHG or charge-induced SHG has been well documented. Nonetheless, it is essential to develop the ability to dynamically control and manipulate the nonlinear properties, preferably at high speed. Plasmonic hot carriers can be resonantly excited in metal nanoparticles and then injected into semiconductors within 10-100 fs, where they eventually decay on a comparable time scale. This allows one to rapidly manipulate all kinds of characteristics of semiconductors, including their nonlinear properties. Here we demonstrate that plasmonically generated hot electrons can be injected from plasmonic nanostructure into bilayer (2L) tungsten diselenide (WSe), breaking the material inversion symmetry and thus inducing an SHG. With a set of pump-probe experiments we confirm that it is the dynamic separation electric field resulting from the hot carrier injection (rather than a simple optical field enhancement) that is the cause of SHG. Transient absorption measurement further substantiate the plasmonic hot electrons injection and allow us to measure a rise time of ∼120 fs and a fall time of 1.9 ps. Our study creates opportunity for the ultrafast all-optical control of SHG in an all-optical manner that may enable a variety of applications.
通过电场感应二次谐波产生（EFISHG）或电荷感应二次谐波产生（CISHG）来调制二次谐波（SHG）已经得到了很好的证明。然而，发展动态控制和操纵非线性特性的能力是至关重要的，最好是在高速下。在金属纳米粒子中可以共振激发等离子体热载流子，然后在 10-100fs 内注入半导体，它们最终在可比的时间尺度上衰减。这使得人们能够快速操纵半导体的各种特性，包括它们的非线性特性。在这里，我们证明了可以将等离子体产生的热电子从等离子体纳米结构注入到双层（2L）二硒化钨（WSe）中，打破材料的反转对称性，从而诱导二次谐波产生。通过一系列泵浦-探测实验，我们证实了导致 SHG 的是热载流子注入产生的动态分离电场（而不是简单的光场增强）。瞬态吸收测量进一步证实了等离子体热电子的注入，并使我们能够测量到约 120fs 的上升时间和 1.9ps 的下降时间。我们的研究为以全光方式超快全光控制二次谐波产生创造了机会，这可能为各种应用开辟道路。
