Remarks on Superluminal Propagation of an Electromagnetic Wave in Air

利用超电离波前在空气中控制激光产生的THz辐射

Steering laser-produced THz radiation in air with superluminal ionization fronts

研究利用飞行聚焦技术控制空气中激光产生的THz辐射方向，实现大角度及后向发射，为远程THz光谱学提供新途径。

Tunable superluminal and subluminal reflected group delay in an air-Weyl semimetal film-Weyl semimetal substrate layered system

In this work, we theoretically investigate the superluminal and subluminal reflected group delay from an air-Weyl semimetal film-Weyl semimetal substrate layered structure by using 4*4 magneto-optical matrix. We show a tunable transition between positive and negative group delays of reflection pulse in such a layered structure controlled by the properties of the Weyl Semimetal layer and reveal its mechanism to control the propagation properties of the light pulse reflected from such structure. It is demonstrated that the reflected group delays are tunable from positive to negative values and v…

Comment on "Observation of Superluminal Behaviors in Wave Propagation"

Mugnai et al. have reported an experiment in which microwave packets appear to travel in air with a speed substantially greater than c. They calculate the group velocity of their packets and find that it agrees with their experimental result. That calculation is incorrect. A correct calculation gives a group velocity less than c. The reported experimental result cannot be reconciled with the Maxwell equations.

Terahertz Wave Guiding by Femtosecond Laser Filament in Air

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…

Propagation of a squeezed optical field in a medium with superluminal group velocity

We investigated the propagation of a squeezed optical field, generated via the polarization self-rotation (PSR) effect, with a sinusoidally-modulated degree of squeezing through an atomic medium with anomalous dispersion. We observed the advancement of the signal propagating through a resonant Rb vapor compared to the reference signal, propagating in air. The measured advancement time grew linearly with atomic density, reaching a maximum of $11 \pm 1~μ$s, which corresponded to a negative group velocity of $v_g\approx - 7,000~$m/s. We also confirmed that the increasing advancement was accompani…

通过行波天线模型揭示空气成丝过程中的太赫兹激光速度效应

Revealing the terahertz-laser velocity effect during air filamentation via travelling-wave-antenna model

本文利用改进的行波天线模型研究了空气成丝中太赫兹相速度与激光群速度之比K的影响，发现K决定太赫兹辐射的远场分布及发射图样转变，为光束整形及判断电离前沿速度提供了理论工具。