Sheng Zhang 1,2†Yongwei Cui 1,2,3Shunjia Wang 1,2Haoran Chen 1,2,3[ ... ]Zhensheng Tao 1,2,*
Author Affiliations
1 Fudan University, State Key Laboratory of Surface Physics, Department of Physics, Shanghai, China
2 Fudan University, Key Laboratory of Micro and Nano Photonic Structures, Shanghai, China
3 Shanghai Research Center for Quantum Sciences, Shanghai, China
4 Beijing Normal University, Center for Advanced Quantum Studies, Department of Physics, Beijing, China
5 Fudan University, Institute for Nanoelectronic Devices and Quantum Computing, Shanghai, China
Precise and ultrafast control over photo-induced charge currents across nanoscale interfaces could lead to important applications in energy harvesting, ultrafast electronics, and coherent terahertz sources. Recent studies have shown that several relativistic mechanisms, including inverse spin-Hall effect, inverse Rashba–Edelstein effect, and inverse spin-orbit-torque effect, can convert longitudinally injected spin-polarized currents from magnetic materials to transverse charge currents, thereby harnessing these currents for terahertz generation. However, these mechanisms typically require external magnetic fields and exhibit limitations in terms of spin-polarization rates and efficiencies of relativistic spin-to-charge conversion. We present a nonrelativistic and nonmagnetic mechanism that directly utilizes the photoexcited high-density charge currents across the interface. We demonstrate that the electrical anisotropy of conductive oxides RuO2 and IrO2 can effectively deflect injected charge currents to the transverse direction, resulting in efficient and broadband terahertz radiation. Importantly, this mechanism has the potential to offer much higher conversion efficiency compared to previous methods, as conductive materials with large electrical anisotropy are readily available, whereas further increasing the spin-Hall angle of heavy-metal materials would be challenging. Our findings offer exciting possibilities for directly utilizing these photoexcited high-density currents across metallic interfaces for ultrafast electronics and terahertz spectroscopy.
terahertz optics ultrafast science nanophotonics 
Advanced Photonics
2023, 5(5): 056006
Author Affiliations
Fudan University, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education) and Department of Physics, State Key Laboratory of Surface Physics, Shanghai, China
Dynamically controlling terahertz (THz) waves with an ultracompact device is highly desired, but previously realized tunable devices are bulky in size and/or exhibit limited light-tuning functionalities. Here, we experimentally demonstrate dynamic modulation on THz waves with a dielectric metasurface in mode-selective or mode-unselective manners through pumping the system at different optical wavelengths. Quasi-normal-mode theory reveals that the physics is governed by the spatial overlap between wave functions of resonant modes and regions inside resonators perturbed by pump laser excitation at different wavelengths. We further design/fabricate a dielectric metasurface and experimentally demonstrate that it can dynamically control the polarization state of incident THz waves, dictated by the strength and wavelength of the pumping light. We finally numerically demonstrate pump wavelength-controlled optical information encryption based on a carefully designed dielectric metasurface. Our studies reveal that pump light wavelength can be a new external knob to dynamically control THz waves, which may inspire many tunable metadevices with diversified functionalities.
dynamic metasurfaces terahertz quasi-normal-mode theory optical pumping 
Advanced Photonics
2023, 5(2): 026005
Author Affiliations
1 Fudan University, Department of Physics and State Key Laboratory of Surface Physics, Shanghai, China
2 Shanghai Research Center for Quantum Sciences, Shanghai, China
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.
chiral terahertz generation active metasurface time-domain terahertz spectroscopy 
Advanced Photonics
2021, 3(5): 056002
复旦大学 物理学系 表面物理国家重点实验室, 上海200438
超快光学 阿秒脉冲 高次谐波 阿秒脉冲测量 阿秒光电子能谱 Ultrafast optics Attosecond pulses High-harmonic generation Attosecond pulse measurement Attosecond photoelectron spectroscopy 
2021, 50(8): 0850204

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