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-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-Investigating the non-radially polarized component of terahertz wave emission during single-colour femtosecond laser filamentation in air

Jiayu Zhao, Hui Gao, Shichang Li, Chang Liu, Yamin Chen, Yan Peng,  Yiming Zhu

http://iopscience.iop.org/article/10.1088/2040-8986/aadef7/pdf

Recently, simultaneous emission of radially and non-radially polarized terahertz (THz) pulses during single-colour femtosecond laser filamentation has been reported. In this work, the latter radiation has been specifically investigated, instead of the well-studied THz radial polarization. Briefly, cut-back measurements have verified that the ellipticity of the generated THz pulse with non-radial polarization decreased (became more linearly polarized) with the increasing filament length. The underlying mechanism responsible for this phenomenon is the existence of a propagation effect of THz wave along the filament plasma channel. In this case, the resulted off-axis propagation of THz wave inside the plasma column played a dominant role on the generated non-radial THz polarization, rather than the expected on-axis THz birefringence induced by the high laser intensity. This discovery will greatly renew the understanding of THz emission from plasma sources.

Abstract-Clue to a thorough understanding of terahertz pulse generation by femtosecond laser filamentation

Jiayu Zhao, Weiwei Liu, Shichang Li, Dan Lu, Yizhu Zhang, Yan Peng, Yiming Zhu, and Songlin Zhuang

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-6-4-296

In this work, it has been demonstrated that in order to fully understand the terahertz (THz) pulse generation process during femtosecond laser filamentation, the interaction between THz wave and air plasma has to be taken into account. This interaction is mainly associated with the spatial confinement of the THz pulse by the plasma column, which could be described by the one-dimensional negative dielectric (1DND) waveguide model. By combining the 1DND model with the conventional four-wave mixing (4WM) and photocurrent (PC) models, the variation of THz spectral amplitude and width obtained in experiments could be better understood. Finally, a three-step procedure, with 1DND bridging 4WM and PC processes, has been established for the first time to describe the underlying mechanism of THz radiation from plasma sources.

© 2018 Chinese Laser Press

Abstract-Strong Spatial Confinement of Terahertz Wave inside Femtosecond Laser Filament

Jiayu Zhao, Wei Chu, Zhi Wang, Yan Peng, Cheng Gong, Lie Lin, Yiming Zhu, Weiwei Liu, Ya Cheng, Songlin Zhuang, and Zhizhan Xu

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/acsphotonics.6b00512

Publication Date (Web): November 8, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.6b00512

In this paper, a new experimental phenomenon is demonstrated. During the femtosecond laser filamentation, the generated terahertz (THz) pulse has been found to be strongly confined inside the plasma channel, reaching a spatial diameter of a few tens of micrometres. It has been attributed to the formation of a plasma negative dielectric waveguide induced by the transverse inhomogeneous plasma density distribution. The new experimental phenomenon will renew the understanding of the THz wave generation and propagation dynamics during the femtosecond laser and air plasma interaction. Due to this strong spatial confinement, THz electric field strength could be enhanced by orders of magnitude, potentially providing a new approach to perform THz nonlinear optics with low laser energy.

Abstract-Terahertz identification and quantification of neurotransmitter and neurotrophy mixture

Yan Peng, Xiaorong Yuan, Xiang Zou, Wanqing Chen, Hui Huang, Hongwei Zhao, Bo Song, Liang Chen, and Yiming Zhu

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-7-11-4472

Terahertz spectroscopy has been widely used for investigating the fingerprint spectrum of different substances. For cancerous tissues, the greatest difficulty is the absorption peaks of various substances contained in tissues overlap with each other, which are hard to identify and quantitative analyze. As a result, it is very hard to measure the presence of cancer cell and then to diagnose accurately. In this paper, we select three typical neurotransmitters (γ-aminobutyric acid, L-glutamic acid, dopamine hydrochloride) and two typical metabolites (inositol and creatine) in neurons to measure their terahertz spectra with different mixture ratios. By choosing characteristic absorption peaks, removing baseline and using the least square method, we can identify the components and proportions of each mixture, where the goodness of fit to practical situation is up to 94%. These results provide important evidences for identifying nerve substances and obtaining exact quantitative analysis.

© 2016 Optical Society of America

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