Giant pattern evolution in third-harmonic generation of strained monolayer WS 2 at two-photon excitonic resonance
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Giant pattern evolution in third-harmonic generation of strained monolayer WS2 at two-photon excitonic resonance Jing Liang1,2,§, He Ma1,2,§, Jinhuan Wang3, Xu Zhou1, Wentao Yu1, Chaojie Ma1, Muhong Wu1, Peng Gao4, Kaihui Liu1,2 (), and Dapeng Yu5 1
State Key Laboratory for Mesoscopic Physics and Frontiers Science Center for Nano-optoelectronics, School of Physics, Peking University, Beijing 100871, China 2 Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, Peking University, Beijing 100871, China 3 School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China 4 International Center for Quantum Materials, Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China 5 Shenzhen Institute for Quantum Science and Engineering, and Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China § Jing Liang and He Ma contributed equally to this work. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 5 May 2020 / Revised: 6 July 2020 / Accepted: 19 July 2020
ABSTRACT Strong geometrical confinement and reduced dielectric screening of two-dimensional (2D) materials leads to strong Coulomb interaction and eventually give rise to extraordinary excitonic effects, which dominates the optical and optoelectronic properties. For nonlinear 2D photonic or optoelectronic applications, excitonic effects have been proved effective to tune the light-matter interaction strength. However, the modulation of excitonic effects on the other aspect of nonlinear response, i.e., polarization dependence, has not been fully explored yet. Here we report the first systemic study on the modulation of excitonic effects on the polarization dependence of second and third harmonic generation (SHG and THG) in strained monolayer WS2 by varying excitation wavelength. We demonstrated that polarization-dependent THG patterns undergo a giant evolution near two-photon excitonic resonance, where the long-axis of the parallel component (originally parallel to the strain direction) has a 90° flip when the excitation wavelength increases. In striking contrast, no apparent variation of polarization-dependent SHG patterns occurs at either two- or three-photon excitonic resonance conditions. Our results open a new avenue to modulate the anisotropic nonlinear optical response of 2D materials through effective control of excitonic resonance states, and thus open opportunity for new designs and applications in nonlinear optoelectronic 2D devices.
KEYWORDS two-dimensional materials, nonlinear optics, excitonic effects
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Introduction
Nonlinear optics is an essential part of modern optics and plays a crucial role in various optical applications including ultrafast pulse laser generation, optical parametric generation/ amplification, optical switches, optical modulators and so forth [1–3]. Nowadays, the increasing development trend of miniaturization and on-chip integration
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