Abstract-Enhancing terahertz radiation from femtosecond laser filaments using local gas density modulation

 

Haicheng Xiao, Shengfeng Wang, Yan Peng, Daniel M. Mittleman, Jiayu Zhao, Zuanming Jin, Yiming Zhu, and Songling Zhuang

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.104.013517?ft=1

We present a method to enhance the terahertz (THz) wave radiation from a femtosecond laser-induced plasma filament by controlling the local gas density within the filament. We develop a theoretical model for THz generation from a laser-induced air plasma filament and the subsequent propagation process, to account for a varying local gas density. By adjusting the local gas density along the filament, the transient current distribution along the filament and the resulting coherent superposition of terahertz waves can be controlled. The location of the gas jet nozzle and the relative phase between multicolor light fields both affect the transient current distribution and thus the strength of the generated THz field. Compared with the conventional terahertz generation by a two-color filament in a homogeneous gas, a three-color filament can realize an increase by 6.12 times in the generated THz pulse energy, with optimized local gas density modulation. Our results suggest that the THz amplification via local gas density modulation can be further improved with well-designed multicolor pulses.

• 
• 
• 
• 
• 
• 

Abstract-Enhancing terahertz radiation from femtosecond laser filaments using local gas density modulation

 

Haicheng Xiao, Shengfeng Wang, Yan Peng, Daniel M. Mittleman, Jiayu Zhao, Zuanming Jin, Yiming Zhu, and Songling Zhuang

https://journals.aps.org/pra/accepted/0e07fN3dFc71701f18f40e30527204af2e708c149

We present a method to enhance the terahertz (THz) wave radiation from a femtosecond laser-induced plasma filament by controlling the local gas density within the filament. We develop a theoretical model for THz generation from a laser-induced air plasma filament and the subsequent propagation process, to account for a varying local gas density. By adjusting the local gas density along the filament, the transient current distribution along the filament and the resulting coherent superposition of terahertz waves can be controlled. The location of the gas jet nozzle and the relative phase between multicolor light fields both affect the transient current distribution and thus the strength of the generated THz field. Compared with the conventional terahertz generation by a two-color filament in a homogeneous gas, a three-color filament can realize a increase by 6.12 times in the generated THz pulse energy, with optimized local gas density modulation. Our results suggest that the THz amplification via local gas density modulation can be further improved with well-designed multicolor pulses

Abstract-Ultrafast terahertz magnetometry

Wentao Zhang, Pablo Maldonado, Zuanming Jin, Tom S. Seifert, Jacek Arabski, Guy Schmerber, Eric Beaurepaire, Mischa Bonn, Tobias Kampfrath, Peter M. Oppeneer, Dmitry Turchinovich

https://www.nature.com/articles/s41467-020-17935-6

A material’s magnetic state and its dynamics are of great fundamental research interest and are also at the core of a wide plethora of modern technologies. However, reliable access to magnetization dynamics in materials and devices on the technologically relevant ultrafast timescale, and under realistic device-operation conditions, remains a challenge. Here, we demonstrate a method of ultrafast terahertz (THz) magnetometry, which gives direct access to the (sub-)picosecond magnetization dynamics even in encapsulated materials or devices in a contact-free fashion, in a fully calibrated manner, and under ambient conditions. As a showcase for this powerful method, we measure the ultrafast magnetization dynamics in a laser-excited encapsulated iron film. Our measurements reveal and disentangle distinct contributions originating from (i) incoherent hot-magnon-driven magnetization quenching and (ii) coherent acoustically-driven modulation of the exchange interaction in iron, paving the way to technologies utilizing ultrafast heat-free control of magnetism. High sensitivity and relative ease of experimental arrangement highlight the promise of ultrafast THz magnetometry for both fundamental studies and the technological applications of magnetism.

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.

• 
• 
• 
• 
• 

Abstract-Terahertz Emission on the Surface of a van der Waals Magnet CrSiTe3

Peng Suo, Wei Xia, Wenjie Zhang, Xiaoqing Zhu, Jibo Fu,  Xian Lin, Zuanming Jin, Weimin Liu, Yanfeng Guo, Guohong Ma

https://onlinelibrary.wiley.com/doi/abs/10.1002/lpor.202000025

The van der Waals magnet CrSiTe3 (CST) has captured immense interest because it is capable of retaining the long‐range ferromagnetic order even in its monolayer form, thus offering potential use in spintronic devices. Bulk CST crystal has inversion symmetry that is broken on the crystal surface. Here, by employing ultrafast terahertz (THz) emission spectroscopy and time resolved THz spectroscopy, the THz emission of the CST crystal is investigated, which shows a strong THz emission from the crystal surface under femtosecond (fs) pulse excitation at 800 nm. Theoretical analysis based on space symmetry of CST suggests the dominant role of shift current occurring on the surface with a thickness of a few quintuple layers in producing the THz emission, consistent with the experimental observation that the emitted THz amplitude strongly depends on the azimuthal and pumping polarization angles. This study offers a new efficient THz emitter as well as a better understanding of the nonlinear optical response of CST. It hopefully will open a window toward the investigation on the nonlinear optical response in the mono/few‐layer van der Waals crystals with low‐dimensional magnetism.

Abstract-Influence of Oxygen Adsorption on the Terahertz Conductivity Spectroscopy of CVD-Grown MoS2 Thin Flims

Xing Xiao, Litao Zhao, Zeyu Zhang, Xian Lin, Yang Yu, Zuanming Jin, Guohong Ma,  Jianquan Yao

https://www.osapublishing.org/abstract.cfm?uri=ISUPTW-2018-ThC4

By employing the time-resolved terahertz spectroscopy, we have investigated the dynamical photoconductivity response of MoS2 laminate in nitrogen, dry air and oxygen, the photoconductivity of MoS2 is dramatically altered by the adsorption of oxygen.

© 2018 OSA

Abstract-Terahertz time-domain spectroscopy for magnonics and magnetotransport

Zuanming Jin, Xiumei Liu, Shunnong Zhang, Wanying Zhao, Xian Lin, Zongzhi Zhang, Chao Jin, Shixun Cao, Zhenxiang Cheng, Guohong Ma, Jianquan Yao,

https://www.osapublishing.org/abstract.cfm?uri=ISUPTW-2018-ThD2

Terahertz (THz) time-domain spectroscopy can be used to investigate the spintronic effects, such as low-energy magnons and magnetotransports, in the ultrafast operation regime, sub-picosecond time scale and/or terahertz frequency range.

© 2018 OSA

Abstract-Mechanical Terahertz Modulation Based on Single-Layered Graphene

Long Cheng, Zuanming Jin, Zongwei Ma, Fuhai Su, Yang Zhao, Yongzhuan Zhang, Tongyu Su, Yan Sun, Xueli Xu, Zhi Meng, Yuecheng Bian, Zhigao Sheng


http://onlinelibrary.wiley.com/doi/10.1002/adom.201700877/full

The 2D terahertz (THz) modulator, enabling efficient manipulation of such versatile band in nanoscale, is crucial for THz microdevices and systems, but its implementation is difficult and remains challenging in practice. Here, a novel 2D THz modulator based on single-layered graphene under mechanical strain is demonstrated. Bidirectional, i.e., both positive and negative, THz modulation effect is realized by utilizing unconventionally distributed strains on graphene. Such mechanical modulation is found to be stable and reversible, and its modulation depth can exceed 26% at 1 THz under 10–2 GPa strain. Observations of both the strain and frequency dependent modulation behavior evidence the mechanical strain-induced change of the Dirac-like energy dispersion in graphene, which is distinctive from that of the electrical and optical approaches. Due to the reliability and wide applicability of mechanical forces, these results provide an alternative route for chip-scale THz modulation devices based on 2D materials.

Abstract-Terahertz Magnon-Polaritons in TmFeO3

Rasing, A. V. Kimel, Kailing Zhang, Zuanming Jin, Shixun Cao, Wei Ren, Guo-Hong Ma, Rostislav Mikhaylovskiy

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.7b01402?mi=aayia761&af=R&AllField=nano&target=default&targetTab=std

Magnon-polaritons are shown to play a dominant role in the propagation of terahertz (THz) waves through TmFeO3 orthoferrite, if the frequencies of the waves are in the vicinity of the quasi-antiferromagnetic spin resonance mode. Both time-domain THz transmission and emission spectroscopies reveal clear beatings between two modes with frequencies slightly above and slightly below this resonance, respectively. Rigorous modelling of the interaction between the spins of TmFeO3 and the THz light shows that the frequencies correspond to the upper and lower magnon-polariton branches. Our findings reveal the previously ignored importance of propagation effects and polaritons in such heavily debated areas as THz magnonics and THz spectroscopy of electromagnons. It also shows that future progress in these areas calls for an interdisciplinary approach at the interface between magnetism and photonics.

Abstract-Photoinduced terahertz radiation and negative conductivity dynamics in Heusler alloy Co2MnSn film

Shunnong Zhang, Zuanming Jin, Xiumei Liu, Wanying Zhao, Xian Lin, Chao Jing, and Guohong Ma

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-16-3080&origin=search

We report the broadband terahertz (THz) radiation in ferromagnetic half-metallic Heusler alloy Co2MnSn${\mathrm{Co}}_2\mathrm{MnSn}$ thin film upon the irradiation of a femtosecond laser pulse at room temperature. The magnetic-, sample symmetry-, and pump fluence-dependent THz emission reveals that the THz radiation is originated from the magnetic-dipole radiation, i.e., the light-induced subpicosecond demagnetization. In addition, by optical pump-THz probe spectroscopy, we found that the photoexcited increase of the scattering rate of hot carriers thereby leads to the photoinduced negative THz conductivity in Co2MnSn${\mathrm{Co}}_2\mathrm{MnSn}$ thin film.

© 2017 Optical Society of America

Abstract-The Role of Photo-Induced Exciton in the Transient Terahertz Conductivity of Few-Layer WS2 Laminate

Xiao Xing, Litao Zhao, Zeyu Zhang, Xiankuan Liu, Kailin Zhang, Yang Yu, Xian Lin, Huaying Chen, Jinquan Chen, Zuanming Jin, Jianhua Xu, and Guo-Hong Ma

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.7b05345?journalCode=jpccck

The exciton effect in two-dimensional (2D) transition metal dichalcogenides (TMDs) plays a dominated role in describing the optical and optoelectronic properties. However, the interplay between the excitons and free carriers has yet to be understood upon the photo excitation in 2D TMDs. Here we first present a study of the dynamical interplay of excitons and unbound electron-hole pairs using time-resolved terahertz (THz) spectroscopy (TRTS) in a few-layer WS2 laminate. Our experimental results demonstrate that the Auger recombination is observed only in the relaxation process of the mobile charge carriers rather than that of excitons upon photoexcitation. The transient complex THz photoconductivity spectroscopy of WS2 is well described by Lorentz oscillator model of free carriers modulated by the exciton polarization field. Our results provide a comprehensive understanding of non-equilibrium carrier kinetics (both excitons and free carriers) in WS2 laminate, and should be applicable to other 2D system.

Abstract-Switchable metamaterial for enhancing and localizing electromagnetic field at terahertz band

Junxing Liu, Kailin Zhang, Xiankuan Liu, Zeyu Zhang, Zuanming Jin, Xiaoyong He, and Guohong Ma

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-13-13944

In this article, a novel metamaterial is designed aimed at generating a single electromagnetic hot spot, in order to realize the localization of the incident electromagnetic field at terahertz band, and this kind of metastructure is an ideal candidate for many research fields such as spintronics, nonlinear magnetic response, near-field optics, and optical antenna, etc. The specially tailored metamaterial takes the shape of diabolo with a metal triangle pair connected by a cubic gallium arsenide (GaAs) gap. We demonstrated by simulation that both electric- and magnetic-field of incident THz pulse can be confined in the small GaAs gap when a synchronized femtosecond laser pulse is illuminated. The numerical simulation results show that 2 orders of magnitude of field enhancement can be obtained for a 1-by-1 μm GaAs gap, and the field enhancement factor can also be further improved by tailoring the GaAs gap down to nanometer scale.

© 2017 Optical Society of America

Abstract-Photo-Induced Terahertz Conductivity and Carrier Relaxation in Thermal-Reduced Multilayer Graphene Oxide Films

Xiao Xing, Litao Zhao, Zeyu Zhang, Liang Fang, Zhengfu Fan, Xiumei Liu, Xian Lin, Jianhua Xu, Jinquan Chen, Xinluo Zhao, Zuanming Jin, and Guo-Hong Ma

J. Phys. Chem. C, Just Accepted Manuscript

DOI: 10.1021/acs.jpcc.6b10580

Publication Date (Web): January 11, 2017

Copyright © 2017 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b10580?journalCode=jpccck

Graphene oxide (GO) is an attractive option for large scale production of graphene. On the other hand, the graphene obtained by the reduction of GO has inevitable structural defects, and the vacant lattice sites will significantly restrict its conductivity. It has been demonstrated that thermal annealing in hydrogen is an efficient method to reduce defects and heal the lattice in GO samples. However, it is still not clear that how the defects and/or disordering influence on the photoelectric conversion efficiency and the carrier relaxation pathway in GO. Herein, the time-domain terahertz (THz) spectroscopy is employed to characterize the properties of the multilayer GO films which were annealed in hydrogen at various temperatures. Upon photo excitation, a transient increase of the conductivity was observed for the reduced graphene oxide (RGO) samples. The ultrafast carrier relaxation process can be well assigned to the carrier-carrier scattering and carrier-phonon coupling. Our results demonstrated that the RGO films with fewer defects and better lattice structure is successfully manufactured. In addition, by fitting to the Drude model, several electron transport parameters, such as the carrier scattering time, carrier plasma frequency and photoinduced conductivity, are obtained in our multilayer RGO films.

Abstract-Terahertz broadband modulation in a biased BiFeO3/Si heterojunction

Xiankuan Liu, Zeyu Zhang, Xian Lin, Kailin Zhang, Zuanming Jin, Zhenxiang Cheng, and Guohong Ma

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-23-26618

A new terahertz (THz) modulator based on bias-driven carrier conductivity change in a heterojunction was proposed. BiFeO3 film and silicon were selected as building blocks for fabricating the THz modulator. THz nonlinear transmission as a function of bias voltage was studied systematically. THz peak transmission as a function of bias shows a similar tendency as the current-voltage response of the heterojunction: the forward bias leads to the exponential enhancement of THz transmission, and in contrast, the reverse bias shows no observable changes in THz transmission. The modulation depth and modulation bandwidth of THz pulse can reach up to 42% and 1.0 THz with forward bias of 4.8 V, respectively. The observed bias dependent THz transmission in the BFO/Si heterojunction is well-interpreted by the proposed model: the diffused carriers across the heterojunction are localized in BFO thin film with applied forward bias. Our finding provides great potential for applications in designing all electrical broadband THz modulators.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstract-Resolving the spin reorientation and crystal-field transitions in TmFeO3 with terahertz transient

• Kailin Zhang
• , Kai Xu
• , Xiumei Liu
• , Zeyu Zhang
• , Zuanming Jin
• , Xian Lin
• , Bo Li
• , Shixun Cao
•  &Guohong Ma

http://www.nature.com/articles/srep23648
Rare earth orthoferrites (RFeO3) exhibit abundant physical properties such as, weak macroscopic magnetization, spin reorientation transition, and magneto-optical effect, especially the terahertz magnetic response, have received lots of attention in recent years. In this work, quasi-ferromagnetic (FM) and quasi-antiferromagnetic (AFM) modes arising from Fe sublattice of TmFeO3 single crystal are characterized in a temperature range from 40 to 300 K, by using terahertz time-domain spectroscopy (THz-TDS). The magnetic anisotropy constants in ac-plane are estimated according to the temperature-dependent resonant frequencies of both FM and AFM modes. Here, we further observe the broad-band absorptions centered ~0.52, ~0.61, and ~1.15 THz below 110 K, which are reasonably assigned to a series of crystal-field transitions (R modes) of ground multiplets (6H3) of Tm3+ ions. Specially, our finding reveals that the spin reorientation transition at a temperature interval from 93 to 85 K is driven by magnetic anisotropy, however, which plays negligible role on the electronic transitions of Tm ions in the absence of applied magnetic fields.

Abstract-Efficient formation of excitons in a dense electron-hole plasma at room temperature

Andreas Hangleiter, Zuanming Jin, Marina Gerhard, Dimitry Kalincev, Torsten Langer, Heiko Bremers, Uwe Rossow, Martin Koch, Mischa Bonn, and Dmitry Turchinovich

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.92.241305

Room-temperature electronic properties of semiconductors, especially in the case of higher charge densities, are commonly discussed in terms of single-particle excitations – free electrons and holes. Many-particle effects, such as the formation of excitons (Coulomb-bound electron-hole pairs), are usually seen as low-temperature and low-density phenomena. In this paper, using ultrafast terahertz and photoluminescence measurements, the authors find that under certain conditions typical for wide-band-gap semiconductors, the radiative excitons can be efficiently formed at high charge density and at room temperature. This effect is believed to contribute to the extraordinarily high quantum efficiency of group III nitride light emitters.

 

Commonly, excitons in semiconductors are regarded as a low-temperature, low carrier density phenomenon, becoming unstable as the temperature and carrier density increase. Contrary to the common expectation, our ultrafast conductivity and luminescence measurements in GaInN/GaN quantum wells reveal a highly efficient formation of radiative excitons from a high-density electron-hole plasma at room temperature, and provide a quantitative measure of the exciton fraction to reach more than 40% at a total carrier population as high as                                                                         

∼10cm−21013cm−2Driven by the mass action of electrons and holes, this effect is believed to contribute to the extraordinarily high quantum efficiency of group-III nitride light emitters.