Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA.
Phys Rev Lett. 2012 Nov 2;109(18):183902. doi: 10.1103/PhysRevLett.109.183902. Epub 2012 Oct 31.
We observe off-axis phase-matched terahertz generation in long air-plasma filaments produced by femtosecond two-color laser focusing. Here, phase matching naturally occurs due to off-axis constructive interference between locally generated terahertz waves, and this determines the far-field terahertz radiation profiles and yields. For a filament longer than the characteristic two-color dephasing length, it emits conical terahertz radiation in the off-axis direction, peaked at 4-7° depending on the radiation frequencies. The total terahertz yield continuously increases with the filament length, well beyond the dephasing length. The phase-matching condition observed here provides a simple method for scalable terahertz generation in elongated plasmas.
我们在飞秒双色激光聚焦产生的长空气等离子体细丝中观察到离轴相位匹配太赫兹产生。在这里，由于局部产生的太赫兹波之间的离轴相长相干，自然会发生相位匹配，这决定了远场太赫兹辐射的分布和产率。对于长于双色退相长度的细丝，它会在离轴方向发射锥形太赫兹辐射，峰值在 4-7°之间，具体取决于辐射频率。总的太赫兹产率连续地随着细丝长度的增加而增加，远远超过了退相长度。这里观察到的相位匹配条件为在拉长的等离子体中产生可扩展的太赫兹提供了一种简单的方法。
