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.

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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-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-Quantitative analysis of homocysteine in liquid by terahertz spectroscopy

Liping Wang, Xu Wu, Yan Peng, Qingrou Yang, Xiaohong Chen, Wanwan Wu, Yiming Zhu, and Songlin Zhuang

(a) Molecular formula of homocysteine, (b) THz spectrum of pure homocysteine powder, (c) variable spectrum of homocysteine aqueous solution as the vacuum drying, (d) time variable amplitudes of absorption peaks corresponding to Fig. 1(c).

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-11-5-2570

Homocysteine (C4H9NO2S) is a variant of the amino acid cysteine, a harmful substance to the human body, which is closely related to cardiovascular disease, senile dementia, fractures, et al. At present, conventional methods for detecting homocysteine in biological samples include high performance liquid chromatography (HPLC), fluorescence polarization immunoassay (FPIA), and enzymatic cycling methods. These methods have the disadvantages of being time-consuming, sample-losing, chemical reagent-using and operation-cumbersome. Here, we present a method for the quantitative detection of homocysteine in liquid based on terahertz spectroscopy. Considering the strong absorption of water for terahertz beam, we also put forward a pretreatment method for drying samples at low temperature. These methods make the detection limit for homocysteine reach 10 µmol/L (human normal concentration). Based on the linear relationship between the homocysteine concentration and the THz spectral intensity, we can successfully achieve quantitative, accurate and real-time detection of homocysteine. As compared to Raman spectroscopy, the correlation coefficient of THz spectrum (R216.24THz${\text{R}}_{16.24\text{THz}}^2$ = 0.99809) is much larger than that of the Raman spectrum (R22558.26cm−1${\text{R}}_{2558.26\text{c}{\text{m}}^{-1}}^2$ = 0.80022, R22937.32cm−1${\text{R}}_{2937.32\text{c}{\text{m}}^{-1}}^2$ = 0.8028). These results are greatly useful for the accurate evaluation of pathological stage.

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

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-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-Predict sample’s line positions of absorption peaks in terahertz band with the forced radiation intensity of molecular electric dipoles

Zhongwei Zhang, Zhi Zhu, Minghui Yuan, Minghui Li, Guanjun You, Lin Chen, Yiming Zhu


https://www.sciencedirect.com/science/article/abs/pii/S0030401819309782

Directly predicting the line positions of samples in the terahertz (THz) band is of significant importance for their THz identification. However, it is really a challenge to gain accurately the line positions by means of theoretical calculation, because the calculation typically involves various parameters, such as level energy and transition moment, which usually we hardly get directly. Based on the classical forced vibration model of dipoles, we propose a quantitative expression, i.e. the forced radiation intensity of molecular electric dipoles, which intend to predict the line positions of absorption peaks in the THz fingerprint spectra of a sample. We verified our expression by 9 recognized frequencies selected from the fingerprint spectra of water vapor in the THz band. Both the line positions and intensities of the absorption peaks of water vapor we calculated by the expression are well consistent with the experimental measurements. The line positions we calculated are also more accurate and comprehensive than that of water clusters simulated from Density Functional Theory (DFT). Our findings further support the theory of coherent superposition to advance a new method to exactly analyze the generation mechanism of molecular THz-fingerprint spectroscopy of a sample.

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.

Abstract-Terahertz spatial sampling with subwavelength accuracy

Yan Peng, Yiming Zhu, Min Gu, Songlin Zhuang

The THz beam passes through an ‘unknown’ object and irradiates from the left surface of the ZnTe detection crystal. The NIR probe beam travels through the SLM and then propagates to the other side of the ZnTe detection crystal carrying the spatial encoded patterns. The probe pattern spatially overlaps with the THz field and temporally overlaps with the peak position of the THz pulse

https://www.nature.com/articles/s41377-019-0185-3

A simple terahertz (THz) spatial sampling method offers kilohertz (kHz) level sampling rates and greatly preserves the energy of a THz pulse, which enables THz imaging detection with a high signal-to-noise ratio, micron-grade accuracy, and subwavelength resolution.

To realize real-time and high-fidelity terahertz (THz) images for applications in THz biodetection and communications, we need to reconstruct the 2D profile of a THz beam with high spatial resolution and accuracy. Over the past several years, THz spatial light modulators (THz-SLM) have enabled quasi-real-time THz imaging with frame rates as fast as one image per 2 s (1/2Hz). This method realized single pixel multiplex THz imaging using an optically controlled reconfigurable THz mask in high-resistivity silicon.

Alternatively, a variety of metamaterial and semiconductor modulation systems have been developed. By exciting free photons in metamaterial or semiconductors, the spatially transmitted THz beam can be effectively modulated.

However, the requirements for high-power THz radiation, sample fabrication, and laser excitation increase the complexity of THz spatial modulation systems. In a recent publication, X.-C. Zhang, R. W. Boyd, and coworkers developed a novel near infrared (NIR)-SLM-based THz spatial sampling method that uses only a normal THz irradiation source while achieving up to kHz level sampling rates and micron-grade accuracy. This method can greatly improve the imaging velocity and imaging quality of THz beams, which is beneficial for the widespread use of THz technology in biomedical and industrial sensing applications. 

The new design is schematically shown in Fig. 1. The entire system mainly consists of a THz beam, an ‘unknown’ object, a spatially encoded NIR beam, a ZnTe detection crystal and a computational algorithm. Compared to previous reports, this novel THz spatial sampling system has several advances. First, the spatial mask is encoded by using an SLM on the NIR probe beam, which can maximally preserve the energy of the THz pulse and therefore improve the signal-to-noise-ratio (SNR) of the imaging system. Second, this method achieves micron-grade accuracy and subwavelength resolution. For a THz wavelength of 940 μm, the resolution is ~λ/15. Third, this THz spatial sampling method can be combined with different algorithms, which can easily adjust between image quality and reconstruction speed. Finally, a thinner electro-optic (EO) detection crystal with a larger nonlinearity and an SLM with a high switching speed can provide better sampling results. These advantages support many important applications, including THz cameras, biomedical sensing, industrial flaw detection, and security inspection.

Abstract-Terahertz wave generation from liquid nitrogen

Alexei V. Balakin, Jean-Louis Coutaz, Vladimir A. Makarov, Igor A. Kotelnikov, Yan Peng, Peter M. Solyankin, Yiming Zhu, and Alexander P. Shkurinov

Fig. 1. Experimental setup. M–dielectric mirror; MM–metallic mirror; BS–beam splitter; 𝜆/2$\lambda /2$–half-wave phase plate; L–lens; PM–off-axis parabolic mirror; BBO–β$\mathrm{\beta }$-barium borate crystal.

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-7-6-678

We present the results of research carried out for the first time, to the best of our knowledge, on the generation of terahertz radiation under the action of “single-color” and “dual-color” high-power femtosecond laser pulses on liquefied gas–liquid nitrogen. Our experimental results supported by careful theoretical interpretation showed clearly that under femtosecond laser radiation, liquid and air emit terahertz waves in a very different way. We assumed that the mobility of ions and electrons in liquid can play an essential role, forming a quasi-static electric field by means of ambipolar diffusion mechanism.

© 2019 Chinese Laser Press

Abstract-Strong tunable photomixing in semi-Dirac materials in the terahertz regime

                                                                   

Sunchao Huang, My Hanh Tran, Jack Zuber, Qian Wang, Yiming Zhu, and Chao Zhang

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-36-2-200

We demonstrate a strong and anisotropic photomixing effect in an electronic system whose energy–momentum dispersion is parabolic in the 𝑥$$ direction and linear in the 𝑦$$ direction, such as a TiO2/VO2${}_{\mathrm{}}{}_{\mathrm{}}$ multilayered structure. The third-order photoresponses along the linear and parabolic directions have been analyzed and determined quantitatively. We have found a remarkable tunability of the mixing efficiency along the parabolic direction by a small electric field in the linear direction, up to two orders of magnitude. In the terahertz (THz) regime, the third-order response is comparable to the linear response under an applied field of 103–104  V/cm${\mathrm{}}^{\mathrm{}}{\mathrm{}}^{\mathrm{}}\mathrm{}$. Additionally, the nonlinear response persists at room temperature. The results may have applications where different current responses are required along different directions in the THz regime.

© 2019 Optical Society of America