Author Affiliations
Abstract
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
作者单位
摘要
1 上海理工大学 光电信息与计算机工程学院,上海 200093
2 上海交通大学 微电子学院,上海 200240
运用时域太赫兹波谱法,低温(10 K)高电场下本征砷化镓中受飞秒激光脉冲激发的电子所辐射出的太赫兹波被准确地测量出来。从样品中辐射出的和电子加速度/减速度成正比的太赫兹电磁波,表现出双极特性。通过分析砷化镓中辐射出的太赫兹波的傅里叶变换谱,在实验上得到阶跃电场下的砷化镓内因电子谷间散射而引起的增益极限频率,可以达到约750 GHz(10 K)。同时通过测量极限频率和温度的关系,发现极限频率是电子经由纵光学声子从L谷到Γ谷的散射能量弛豫过程所需要的时间决定的。通过理论计算电子在Γ谷的弹道加速、电子谷间散射和电子经由纵光学声子连续散射在Γ谷的弛豫等过程的时间得出的增益极限频率与实验值吻合得较好。
光谱学 砷化镓 电子谷间散射 增益 时域太赫兹波谱法 非平衡载流子 spectroscopy GaAs electrons intervalley transfer gain time-domain terahertz spectroscopy nonequilibrium carriers 
中国激光
2010, 37(3): 658
作者单位
摘要
1 上海理工大学光学与电子信息工程学院, 上海 200093
2 上海交通大学微电子学院, 上海 200240
利用时域太赫兹波谱系统,研究了超高电场下砷化镓中的非平衡载流子的动态运动过程。研究发现,当电场小于50 kV/cm时,电子运动所辐射出的太赫兹波信号的最初峰值ΔETHz(对应电子在Γ谷中的加速)随着电场的增加不断增大; 当电场大于50 kV/cm时,ΔETHz随着电场的增大逐渐衰减并最终达到饱和。这一实验结果表明,当电场强度大于50 kV/cm时,由砷化镓中的电子的有效加速质量随着电场的增加而显著地增加(在300 kV/cm的情况下电子的有效加速质量约为低电场时的30倍)。导致这一结果的原因是在超高电场的情况下砷化镓中的能带会发生强烈的混合。
测量 电子飞秒加速 非平衡载流子 时域太赫兹波谱法 measurement femtosecond electron acceleration nonequilibrium carriers time-domain terahertz spectroscopy 
中国激光
2009, 36(2): 328

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