High-efficiency Sub-single-cycle THz Wave Generation by Three-color Air Plasma

THz pulses generation from 3-color $({\omega-2\omega-3\omega})$ air plasma is experimentally investigated. THz yield enhancement factor up to 45 is measured compared to the 2-color (w-2w) case. With 40 fs optical pump pulses, the generated THz pulse spectrum is spanning from below 3 to more than $\mathbf{300} \ \boldsymbol{\mu} \mathbf{m}$ (or from $ \ \mathrm{100} \ \mathbf{THz})$ and supporting sub-5 fs sub-single-cycle far/mid-IR pulses.