Browsing by Author "Hu, Zhiqiang"

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    Creating a near-perfect circularly polarized terahertz beam through the nonreciprocity of a magnetoplasma
    (Optica Publishing Group, 2023) Ju, Xuewei; Hu, Zhiqiang; Zhu, Guofeng; Huang, Feng; Chen, Yanqing; Guo, Cuixia; Belyanin, Alexey; Kono, Junichiro; Wang, Xiangfeng
    Compared to other parts of the electromagnetic spectrum, the terahertz frequency range lacks efficient polarization manipulation techniques, which is impeding the proliferation of terahertz technology. In this work, we demonstrate a tunable and broadband linear-to-circular polarization converter based on an InSb plate containing a free-carrier magnetoplasma. In a wide spectral region (∼ 0.45 THz), the magnetoplasma selectively absorbs one circularly polarized mode due to electron cyclotron resonance and also reflects it at the edges of the absorption band. Both effects are nonreciprocal and contribute to form a near-zero transmission band with a high isolation of –36 dB, resulting in the output of a near-perfect circularly polarized terahertz wave for an incident linearly polarized beam. The near-zero transmission band is tunable with magnetic field to cover a wide frequency range from 0.3 to 4.8 THz.
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    Tunable ultrasharp terahertz plasma edge in a lightly doped narrow-gap semiconductor
    (Optical Society of America, 2021) Ju, Xuewei; Hu, Zhiqiang; Huang, Feng; Wu, Haibin; Belyanin, Alexey; Kono, Junichiro; Wang, Xiangfeng
    Plasma edges in metals typically occur in the visible range, producing characteristic colors of metals. In a lightly doped semiconductor, the plasma edge can occur in the terahertz (THz) frequency range. Due to low scattering rates and variable electron densities in semiconductors, such THz plasma edges can be extremely sharp and greatly tunable. Here, we show that an ultrasharp THz plasma edge exists in a lightly n-doped InSb crystal with a record-high transmittance slope of 80 dB/THz. The frequency at which this sharp edge happens can be readily tuned by changing the temperature, electron density, scattering rate, and sample thickness. The edge frequency exhibited a surprising increase with decreasing temperature below 15 K, which we explain as a result of a weak-to-strong transition in the scattering rate, going from ωτ  ≫ 1 to ωτ ∼ 1. These results indicate that doped narrow-gap semiconductors provide a versatile platform for manipulating THz waves in a controllable manner, especially as a high-pass filter with an unprecedented on/off ratio.