Coherent control of boosted terahertz radiation from air plasma pumped by a femtosecond three-color sawtooth field

We report on the coherent control of boosted ultrashort terahertz pulses emitted from air plasma pumped by a femtosecond sawtooth pulse composed of three optical harmonic fields. With an inline optical setup, the relative phases between the three optical components of the pump pulse can be varied independently with attosecond precision without the complexity of external phase stabilization. We observe that the amplitude of the terahertz emission pumped by the phase-optimized sawtooth wave is enhanced by 1.8 times compared to the widely used two-color scheme. Moreover, by manipulating the relative phases between the three colors at attosecond precision, coherent control of the azimuthal angle, ellipticity, and polarity of terahertz radiation is achieved. A local current model reproduces the coherent control observations well.