Invited Paper

Nonlinear terahertz effects of gold nanofilms

¹ School of Electronic and Information Engineering, Beihang University, Beijing 100191, China
² Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
³ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

^* Email: xiaojunwu@buaa.edu.cn

Received: 26 March 2021

Abstract

Nonlinear interaction between strong-field terahertz electromagnetic waves and matters will become one of the next hot research frontiers in nonlinear optics. However, the lack of strong terahertz radiation sources and appropriate nonlinear terahertz materials have impeded its progress. Here we systematically have investigated the strong-field terahertz nonlinear effects of gold (Au) nanofilms on different substrates, including SiO₂, high-resistivity Si and SiO₂-high-resistivity Si hybrid substrates. The strong-field terahertz waves are emitted from lithium niobate crystals via tilted pulse front technique, and obvious nonlinear transmission responses are observed along with varying the incident field strengths for all the Au samples on the three types of the substrates. The nonlinear behavior is enhanced when the gold nanofilm thickness increases, which can be qualitatively understood by introducing the quantum tunneling effect and carrier multiplication theory generated at the Au nano-slits under the illumination of the strong-field terahertz pulses. Our demonstrations not only open a new paradigm for nonlinear terahertz investigations and future high-speed terahertz devices, but also provide an effective platform for exploring extreme terahertz sciences.