• Advanced Photonics
  • Vol. 3, Issue 5, 056002 (2021)
Changqin Liu1、2、†, Shunjia Wang1, Sheng Zhang1, Qingnan Cai1, Peng Wang1, Chuanshan Tian1, Lei Zhou1、*, Yizheng Wu1、2、*, and Zhensheng Tao1、*
Author Affiliations
  • 1Fudan University, Department of Physics and State Key Laboratory of Surface Physics, Shanghai, China
  • 2Shanghai Research Center for Quantum Sciences, Shanghai, China
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    The ability to generate and manipulate broadband chiral terahertz waves is essential for applications in material imaging, terahertz sensing, and diagnosis. It can also open up new possibilities for nonlinear terahertz spectroscopy and coherent control of chiral molecules and magnetic materials. The existing methods, however, often suffer from low efficiency, narrow bandwidth, or poor flexibility. Here, we propose a novel type of laser-driven terahertz emitters, consisting of metasurface-patterned magnetic multilayer heterostructures, that can overcome the shortcomings of the conventional approaches. Such hybrid terahertz emitters combine the advantages of spintronic emitters for being ultrabroadband, efficient, and highly flexible, as well as those of metasurfaces for the powerful control capabilities over the polarization state of emitted terahertz waves on an ultracompact platform. Taking a stripe-patterned metasurface as an example, we demonstrate the efficient generation and manipulation of broadband chiral terahertz waves. The ellipticity can reach >0.75 over a broad terahertz bandwidth (1 to 5 THz), representing a high-quality and efficient source for few-cycle circularly polarized terahertz pulses with stable carrier waveforms. Flexible control of ellipticity and helicity is also demonstrated with our systematic experiments and numerical simulations. We show that the terahertz polarization state is dictated by the interplay between laser-induced spintronic-origin currents and the screening charges/currents in the metasurfaces, which exhibits tailored anisotropic properties due to the predesigned geometric confinement effects. Our work opens a new pathway to metasurface-tailored spintronic emitters for efficient vector-control of electromagnetic waves in the terahertz regime.

    Video Introduction to the Article

    1 Introduction

    Coherent terahertz sources driven by femtosecond laser pulses can now routinely generate sub-picosecond few-cycle terahertz waves with exceptionally stable carrier waveforms, which can be used in numerous fundamental studies and practical applications.1,2 The ability to manipulate the three-dimensional (3D) electric-field vector of such broadband terahertz waveforms can substantially broaden the applications of the terahertz technologies and open up new possibilities for studies of coherent light–matter interactions,36 as well as of novel ultrafast quantum control facilitated by phase-stable strong terahertz fields.79 Therefore, a great amount of research has been devoted to generating chiral terahertz waves and realizing full control over the 3D field-vectors in their amplitude, phase, frequency, polarization, and spatial properties. Hitherto, the existing methods can be categorized into: (1) direct generation from gas plasmas, e.g., by applying external fields1013 or a combined two-color laser scheme,14,15 but these methods are only applicable for high-energy mJ-level laser amplifiers; (2) special frequency-conversion techniques in nonlinear crystals,16,17 magnetic,18 and novel topological materials,19,20 yet the generation efficiency is usually low; and (3) implementation of passive optical components, such as terahertz polarizers21 and waveplates,22,23 yet they are often limited to narrow bandwidth. So, it still attracts great interest to develop a flexible and robust solution for the efficient generation of broadband chiral terahertz waves.

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    Changqin Liu, Shunjia Wang, Sheng Zhang, Qingnan Cai, Peng Wang, Chuanshan Tian, Lei Zhou, Yizheng Wu, Zhensheng Tao. Active spintronic-metasurface terahertz emitters with tunable chirality[J]. Advanced Photonics, 2021, 3(5): 056002
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    Category: Research Articles
    Received: Jul. 16, 2021
    Accepted: Sep. 29, 2021
    Posted: Oct. 8, 2021
    Published Online: Oct. 26, 2021
    The Author Email: Zhou Lei (phzhou@fudan.edu.cn), Wu Yizheng (wuyizheng@fudan.edu.cn), Tao Zhensheng (zhenshengtao@fudan.edu.cn)