Off-Axis Phase-Matched Terahertz Emission from Two-Color Laser-Induced Plasma Filaments

Phys. Rev. Lett. 109, 183902 (2012)https://ireap.umd.edu/10.1103/PhysRevLett.109.1839022012Journal ArticlePlasma, Accelerator, and Nuclear Physics

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.