Andreeva V A, Kosareva O G, Panov N A, Shipilo D E, Solyankin P M, Esaulkov M N, González de Alaiza Martínez P, Shkurinov A P, Makarov V A, Bergé L, Chin S L
Faculty of Physics, Lomonosov Moscow State University, 119991 Leninskie gori 1/2, Moscow, Russia.
International Laser Center, Lomonosov Moscow State University, 119991 Leninskie gori 1/62, Moscow, Russia.
Phys Rev Lett. 2016 Feb 12;116(6):063902. doi: 10.1103/PhysRevLett.116.063902. Epub 2016 Feb 11.
We have solved the long-standing problem of the mechanism of terahertz (THz) generation by a two-color filament in air and found that both neutrals and plasma contribute to the radiation. We reveal that the contribution from neutrals by four-wave mixing is much weaker and higher in frequency than the distinctive plasma lower-frequency contribution. The former is in the forward direction while the latter is in a cone and reveals an abrupt down-shift to the plasma frequency. Ring-shaped spatial distributions of the THz radiation are shown to be of universal nature and they occur in both collimated and focusing propagation geometries. Experimental measurements of the frequency-angular spectrum generated by 130-fs laser pulses agree with numerical simulations based on a unidirectional pulse propagation model.
我们解决了空气中双色细丝产生太赫兹（THz）的机制这一长期存在的问题，并发现中性粒子和等离子体都对辐射有贡献。我们揭示，四波混频中中性粒子的贡献比独特的等离子体低频贡献要弱得多且频率更高。前者沿向前方向，而后者呈锥形，并显示出向等离子体频率的突然下移。太赫兹辐射的环形空间分布显示具有普遍性质，并且它们在准直和聚焦传播几何结构中都会出现。对130飞秒激光脉冲产生的频率 - 角度光谱的实验测量结果与基于单向脉冲传播模型的数值模拟结果相符。
