Andrey V. Koribut, Georgy E. Rizaev, Daria V. Mokrousova, Sergey A. Savinov, Aleksei A. Reutov, Yurii A. Mityagin, Leonid V. Seleznev, Andrey A. Ionin
Influence of plasma channel length on angular THz radiation pattern is studied experimentally. It is shown that the angular distribution of THz radiation depends only on the focusing conditions and does not depend on the length of the plasma channel. A qualitative explanation of the screening of THz radiation by a filament plasma is proposed
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Femtosecond laser filament generates strong terahertz (THz) pulse in air. In this paper, THz pulse waveform generated by femtosecond laser filament has been experimentally investigated as a function of the length of the filament. Superluminal propagation of THz pulse has been uncovered, indicating that the filament creates a THz waveguide in air. Numerical simulation has confirmed that the waveguide is formed because of the radially non-uniform refractive index distribution inside the filament. The underlying physical mechanisms and the control techniques of this type THz pulse generation meth…
Terahertz (THz) imaging provides cutting edge technique in biology, medical sciences and non-destructive evaluation. However, due to the long wavelength of the THz wave, the obtained resolution of THz imaging is normally a few hundred microns and is much lower than that of the traditional optical imaging. We introduce a sub-wavelength resolution THz imaging technique which uses the THz radiation generated by a femtosecond laser filament in air as the probe. This method is based on the fact that the femtosecond laser filament forms a waveguide for the THz wave in air. The diameter of the THz be…
We theoretically and numerically study the influence of both instantaneous and Raman-delayed Kerr nonlinearities as well as a long-wavelength pump in the terahertz (THz) emissions produced by two-color femtosecond filaments in air. Although the Raman-delayed nonlinearity induced by air molecules weakens THz generation, four-wave mixing is found to impact the THz spectra accumulated upon propagation via self-, cross-phase modulations and self-steepening. Besides, using the local current theory, we show that the scaling of laser-to-THz conversion efficiency with the fundamental laser wavelength …
Near-field perturbation of laser filament enabling simultaneous far-field THz diagnosis and broadband calculus processing
通过近场扰动实现激光丝的远场THz诊断和宽带微分处理，提升等离子体-THz相互作用的理解并推动新型全光学信号处理技术。
We theoretically study the generation of terahertz (THz) radiation by two-color filamentation of ultrashort laser pulses with different wavelengths. We consider wavelengths in the range from 0.6 to 10.6 $μ$m, thus covering the whole range of existing and future powerful laser sources in the near, mid and far-infrared. We show how different parameters of two-color filaments and generated THz pulses depend on the laser wavelength. We demonstrate that there is an optimal laser wavelength for two-color filamentation that provides the highest THz conversion efficiency and results in generation of e…
Coherent generation and control of tunable narrowband THz radiation from laser-induced air-plasma filament
本研究通过时间展宽的双色激光脉冲序列拍频诱导空气等离子体丝，实现了载波包络相位可控且频率可调谐的窄带太赫兹辐射的相干产生与控制，并经数值模拟验证了其可行性。
Axisymmetric model for 1-color laser filament THz emission
本研究提出一种用于单色激光光丝THz发射计算的三维轴对称光束传播模型，结合两种THz发射模型验证发现，非线性传播对THz信号振幅影响大，对频率成分和角分布影响极小。
We report on an optical frequency comb with 14nm (~1.8 THz) spectral bandwidth at -3 dB level that is generated using a passively mode-locked quantum-well (QW) laser in photonic integrated circuits (PICs) fabricated through an InP generic photonic integration technology platform. This 21.5-GHz colliding-pulse mode-locked laser cavity is defined by on-chip reflectors incorporating intracavity phase modulators followed by an extra-cavity SOA as booster amplifier. A 1.8-THz-wide optical comb spectrum is presented with ultrafast pulse that is 0.35-ps-wide. The radio frequency beat note has a 3-dB …
Frequency-angular distributions for THz emission in the range of 0.1 - 3 THz generated in a single-color laser filament plasma situated both under and without electrostatic field are for the first time experimentally studied. The angular distribution for various spectral components of this THz emission is demonstrated to differ significantly. The maximal propagation angles for these components grow up under the electric field, the angular distribution for the low-frequency THz emission depending significantly on the laser pulse energy in contrast to the case of no electric field. An increase i…
Waveform-controlled Terahertz (THz) radiation is of great importance due to its potential application in THz sensing and coherent control of quantum systems. We demonstrated a novel scheme to generate waveform-controlled THz radiation from air plasma produced when carrier-envelope-phase (CEP) stabilized few-cycle laser pulses undergo filamentation in ambient air. We launched CEP-stabilized 10 fs-long (~ 1.7 optical cycles) laser pulses at 1.8 μm into air and found that the generated THz waveform can be controlled by varying the filament length and the CEP of driving laser pulses. Calculations …
In the world of epsilon-near-zero (ENZ) materials, the plasma is unique for its natural ENZ properties at the plasma frequency (wp). However, for the air plasma during femtosecond laser filamentation with wp in terahertz (THz) band, which is also known as a broadband THz emitter, the possible ENZ effect has long been neglected. In this work, interactions between the laser plasma in air and the radiated THz waves were investigated, and the THz resonance absorption at the ENZ point, which gave rise to the generation of surface plasmon waves, has been theoretically and experimentally demonstrated…
Single-Shot Local Measurement of Terahertz Correlated Second Harmonic Generation in Laser Air Plasma Filaments
提出一种基于光学探针混入飞秒激光空气等离子体丝的单次检测太赫兹相关二次谐波产生的方法，利用时空畸变探针束在CCD上获取轨迹，实现了22 fs/pixel分辨率，为无带宽限制的单次THz检测开辟了途径。
Generation and characterization of coherent terahertz radiation from 100-TW laser-wakefield acceleration
100-太瓦激光等离子体加速驱动下，通过实验发现相干集体发射机制产生宽带亚皮秒太赫兹辐射，其能量与电荷和激光能量呈二次关系。
Experimental Realization of All-Optical Terahertz Attoclock
本研究提出了一种全光学太赫兹阿托克时，通过检测THz辐射重建光电离动力学，为研究隧道动力学提供了新的非接触探测方法。
Waveshape of THz radiation produced by two-color laser-induced air plasmas
本研究提出增强型锥形发射模型，理论分析双色激光空气等离子体产生太赫兹辐射的空间光谱分布，揭示有效等离子体长度与退相长度差异，并发现光学像差降低转换效率并致光谱不对称。
Terahertz Generation through Photon Deceleration of Long-Wavelength Infrared Laser Pulses in Plasma
研究通过单色长波红外激光脉冲与气态靶相互作用产生太赫兹，用粒子模拟研究机制、分析特性，确定关键参数影响，得出激光到太赫兹能量转换效率约4%等结果，为下一代高能太赫兹源发展提供见解。
Quantum Hydrodynamic Framework of Coherent Terahertz Emission in MXenes Driven via Engineered Femtosecond Waveforms
本文开发了一种多尺度密度矩阵理论，结合紧束缚哈密顿量与Redfield主方程，揭示了MXenes中相干太赫兹发射的微观机制，为增强宽带太赫兹产生提供了设计策略。
Platforms for all-optical computing possess photonic circuits made of silicon-based channels, metal wires or optical fibers, etc. However, such solid waveguides suffer from the lack of reversibility and reconfigurability if facing the next generation of light-guiding-light (LGL) computing scheme, which envisions circuitry-free and rapidly reconfigurable systems powered by dynamic interactions between light beams. Here, we proposed the ubiquitous air as a restorable LGL signal manipulation medium with transient air-plasma waveguide circuits. Briefly, by focusing femtosecond laser beams in the f…
We have performed terahertz (THz)-time domain spectroscopy in various geometries, for characterizing the directivity of THz waves emitted from groove-patterned InAs structures. First, we have distinguished the THz emission mechanisms as a function of epilayer thickness. The carrier drift was predominant in thin sample group (10-70 nm) which the electronic diffusion motion was overriding the oppositely aligned drifting dipoles in thick sample group (370-900 nm) as revealed via amplitude and phase variations. By combined use of the electron-beam lithography and the inductively coupled plasma etc…
Analysis of laser polarization state on remote induced plasma luminescence characteristics of filament in air
本文研究了激光偏振状态对远程飞秒激光成丝诱导等离子体荧光特性的影响，发现线偏振比圆偏振产生更强的337 nm荧光信号，并探讨了其物理机制及在遥感中的潜在应用。
Hybrid terahertz emitter for pulse shaping and chirality control
针对太赫兹应用因需外部调制器而受限的问题，本文提出集成自旋电子发射器与半导体光电导天线PCA的混合太赫兹源，通过双波长激发和参数调控实现无外部组件的脉冲整形与手性控制，为工程化太赫兹辐射提供平台。
Terahertz (THz) radiation is a powerful tool with widespread applications ranging from imaging, sensing, and broadband communications to spectroscopy and nonlinear control of materials. Future progress in THz technology depends on the development of efficient, structurally simple THz emitters that can be implemented in advanced miniaturized devices. Here we show how the natural electronic anisotropy of layered conducting transition metal oxides enables the generation of intense terahertz radiation via the transverse thermoelectric effect. In thin films grown on offcut substrates, femtosecond l…
Spatiotemporal control of two-color terahertz generation
该研究利用时空结构化双色激光脉冲的可编程速度强度峰，实现对THz辐射发射角、焦斑与光谱的控制，并获得高度可聚焦的轴上辐射。
We investigate the generation of broadband terahertz (THz) pulses with phase singularity from air plasmas created by fundamental and second harmonic laser pulses. We show that when the second harmonic beam carries a vortex charge, the THz beam acquires a vortex structure as well. A generic feature of such THz vortex is that the intensity is modulated along the azimuthal angle, which can be attributed to the spatially varying relative phase difference between the two pump harmonics. Fully space and time resolved numerical simulations reveal that transverse instabilities of the pump further affe…
Magnetic domain scanning imaging using phase-sensitive THz-pulse detection
本文提出利用相位敏感太赫兹脉冲探测对CoFeB/Pt自旋电子发射器中的磁畴进行扫描成像，通过近场技术将分辨率提升至个位数微米，并结合Kerr显微镜验证，展示了超越Abbe衍射极限的高分辨磁结构探测能力。
Chiral Terahertz Amplification and Lasing using Two-Dimensional Materials with Berry Curvature Dipole
利用二维材料中的 Berry 曲率偶极实现手性太赫兹放大与激光，通过谐振腔增强光-物质相互作用，实现电驱动相干 THz 辐射。
Far-field model of two-color laser driven terahertz radiation including field element interference and plasma response
针对双色激光驱动太赫兹辐射角分布凹陷及波形振荡尾迹问题，提出包含场元干涉与等离子体响应的远场模型，通过引入时间干涉修正角分布并解释振荡尾迹成因。
Directional intense terahertz radiation driven by abruptly autofocusing lasers in air
针对双色激光空气太赫兹源存在锥形角分布、能量与方向性不足的问题，本研究利用突然自聚焦激光束消除该分布，将太赫兹方向性和强度提升17倍，揭示了失相抑制的物理机制，方案易实现。
Physical mode analysis of multimode cascaded nonlinear processes in strongly-coupled waveguides
本文实验研究了氮化硅波导电路中空间多模非线性相互作用的片上控制，利用强耦合双芯波导的色散差异和模式分解技术，实现了多超模受控激发，并观察到双超模超连续谱生成与级联四波混频导致的第三次谐波上转换现象。
Four-wave mixing and secondary radiations generated by nonharmonic two-color filaments in air: Influence of the Kerr and plasma nonlinearities
本文通过实验和数值模拟研究了空气中非谐双色飞秒细丝产生的四波混频及二次辐射，分析了克尔和等离子体非线性在频率转换中的作用。
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