Abstract-Magnetic Modulation of Terahertz Waves via Spin-Polarized Electron Tunneling Based on Magnetic Tunnel Junctions

Zuanming Jin, Jugeng Li, Wenjie Zhang, Chenyang Guo, Caihua Wan, Xiufeng Han, Zhenxiang Cheng, Chao Zhang, Alexey V. Balakin, Alexander P. Shkurinov, Yan Peng, Guohong Ma, Yiming Zhu, Jianquan Yao, and Songlin Zhuang

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.14.014032

Magnetic tunnel junctions (MTJs) are a key technology in modern spintronics because they are the basis of read-heads of modern hard disk drives, nonvolatile magnetic random access memories, and sensor applications. In this paper, we demonstrate that tunneling magnetoresistance can influence terahertz (THz) wave propagation through a MTJ. In particular, various magnetic configurations between parallel state and antiparallel state of the magnetizations of the ferromagnetic layers in the MTJ have the effect of changing the conductivity, making a functional modulation of the propagating THz electromagnetic fields. Operating in the THz frequency range, a maximal modulation depth of 60% is reached for the parallel state of the MTJ with a thickness of 77.45 nm, using a magnetic field as low as 30 mT. The THz conductivity spectrum of the MTJ is governed by spin-dependent electron tunneling. It is anticipated that the MTJ device and its tunability scheme will have many potential applications in THz magnetic modulators, filtering, and sensing.

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Abstract-Ultrafast photoexcitation dynamics of ZnTe crystals by femtosecond optical pump‐probe and terahertz emission spectroscopy

Jianrui Liu, Xinzhong Chen,   Ziheng Yao, Xincheng Wu,   Mengkun Liu, Alexey V. Balakin,   Alexander P. Shkurinov, Guanjun You, Yiming Zhu

https://onlinelibrary.wiley.com/doi/abs/10.1002/mop.32392

In this work we perform ultrafast optical pump‐optical probe (OPOP) and optical pump terahertz (THz) emission (OPTE) studies on the ultrafast excitation dynamics in <110> ZnTe crystals. Ultrafast two‐photon absorption and coherent phonon are revealed in OPOP measurements. Pump‐power‐ and polarization‐dependent phonon dynamics are characterized in time‐resolved transmission, reflection, and Kerr rotation using OPOP. The phonon polariton‐induced THz emission is directly observed in the time domain of OPTE dynamics. It is clear that the transverse optical phonon at ~3.7 THz and phonon polariton at ~2.6 THz are evident in OPOP measurement while OPTE only reveals part of the polariton dynamics.

Abstract-Terahertz-frequency temporal differentiator enabled by a high-Q resonator

Jingya Xie, Xi Zhu, Hongxiang Zhang, Xiaofei Zang, Lin Chen, Alexey V. Balakin, Alexander P. Shkurinov, and Yiming Zhu

Schematic of the experimental setup for measurements of THz integrated temporal differentiator. AWG: arbitrary waveform generators. RF&MSG: radio frequency microwave source. SGX Module: signal generator extension module. HA: horn antenna. DD: direct detector. The insets (a) and (b) are the schematic drawing of the TRR and cross-sectional view of waveguides, respectively.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-6-7898

Terahertz (THz) fundamental “building blocks” equivalent to those used in multi-functional electronic circuits are very helpful for actual applications in THz data-processing technology and communication. Here, we theoretically and experimentally demonstrate a THz temporal differentiator based on an on-chip high-quality (Q) factor resonator. The resonator is made of low-loss high-resistivity silicon material in a monolithic, integrated platform, which is carefully designed to operate near the critical coupling region. The experiment demonstrates that the device can perform the first-order time derivative of the input signal electric field complex envelope at 214.72 GHz. Our investigation provides an effective approach for terahertz pulse re-shaping and real-time differential computing units.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-THz generation from laser-induced breakdown in pressurized molecular gases: on the way to terahertz remote sensing of the atmospheres of Mars and Venus

Petr M. Solyankin, Irina A. Nikolaeva, Andrew Angeluts, Daniil E. Shipilo, Nikita Minaev,  Nikolay A. Panov, Alexey V. Balakin, Yiming Zhu, Olga Kosareva,  Alexander P. Shkurinov

https://iopscience.iop.org/article/10.1088/1367-2630/ab60f3/meta

The present paper studies the generation of terahertz (THz) radiation in CO2 in comparison with atmospheric air at a wide range of pressures. We established experimentally and explained theoretically that for these gases there are optimal pressures at about 1 bar for air and 0.5 bar for CO2 under which the efficiency of conversion from near-infrared to THz frequencies is the highest. We consider the possibility of applying femtosecond laser-induced THz generation for the study of the atmosphere of Mars and found that the overall THz yield near the surface of Mars is just a factor of 6 lower than on Earth. Comparable THz energy on the two planets is associated with underdense plasma on Earth (~10% of neutrals) and full double ionization of carbon dioxide on Mars (~200% of neutrals), the latter opening great perspective for THz remote sensing of trace gases in the Martian atmosphere.

Abstract- Metal-graphene hybridized plasmon induced transparency in the terahertz frequencies

Anqi Yu, Xuguang Guo, Yiming Zhu, Alexey V. Balakin, Alexander P. Shkurinov,

(a) The proposed split T-shape metal/dielectric/graphene structure. (b) The top view of the proposed structure.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-24-34731

In this work, metal-graphene hybridized plasmon induced transparency (PIT) is systematically studied in the proposed simple metal/dielectric/graphene system. The PIT effect is the result of the coupling between the bright dipolar modes excited in the graphene regions under the shorter metallic bars and the dark quadrupolar modes excited in the graphene regions under the longer metallic bars. The coupled Lorentz oscillator model is used to help explain the physical origin of the PIT effect. Other than being tuned by the distance and the lateral displacement of the orthogonal metallic bars, the coupling efficiency can be further enhanced by the in-phase coupling or quenched by the out-of-phase coupling between the adjacent unit cells. Reduced barrier thickness will result in the enhancement of the coupling strengths and the scaling down of the device. Finally, we show that the PIT window can be actively tuned by changing the Fermi energy of graphene. The proposed structure has potential applications in actively tunable THz modulators, sensors and filters.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-A Multi‐Foci Metalens with Polarization‐Rotated Focal Points

Xiaofei Zang, Hongzhen Ding,   Yuttana Intaravanne,   Lin Chen,   Yan Peng,   Jingya Xie,   Qinghong Ke,   Alexey V. Balakin,   Alexander P. Shkurinov,   Xianzhong Chen, Yiming Zhu,   Songlin Zhuang,

https://onlinelibrary.wiley.com/doi/abs/10.1002/lpor.201900182

Benefiting from the unprecedented capability of metasurfaces in the manipulation of light propagation, metalenses can provide novel functions that are very challenging or impossible to achieve with conventional lenses. Here, an approach to realizing multi‐foci metalenses is proposed and experimentally demonstrated with polarization‐rotated focal points based on geometric metasurfaces. Multi‐foci metalenses with various polarization rotation directions are developed using silicon pillars with spatially variant orientations. The focusing characteristic and longitudinal polarization‐dependent imaging capability are demonstrated upon the illumination of a linearly polarized light beam. The uniqueness of this multi‐foci metalens with polarization‐rotated focal points may open a new avenue for imaging, sensing, and information processing.