arXiv2017
High-energy, carrier-envelope phase (CEP)-stable, sub-cycle, mid-infrared (mid-IR) pulses can provide unique opportunities of exploring phase-sensitive strong-field light-matter interactions in atoms, molecules, and solids. In the mid-IR wavelength, the ponderomotive energy of laser pulses is dramatically increased (versus the visible/near-infrared) and, therefore, the Keldysh parameter is much smaller than unity even at relatively modest laser intensities. This enables to study the sub-cycle electron dynamics in solids via high-harmonic generation (HHG) without damage. One can also control the electron emissions from nano-devices in the sub-cycle time scale. These efforts are opening a great opportunity towards petahertz electronics. Here, we present a high-energy, sub-cycle pulse synthesizer based on a mid-IR optical parametric amplifier (OPA), pumped by CEP-stable, 2.1 um femtosecond pulses, and its application to HHG in solids. The signal and idler combined spectrum spans from 2.5 to 9.0 um, which covers the whole midwave-infrared (MWIR) region. We coherently synthesize the passively CEP-stable few-cycle signal and idler pulses to generate 33 uJ, 0.88-cycle (12.4 fs), multi-GW pulses centered at ~4.2 um, which is further energy scalable. The in-line synthesis of the CEP-stable sub-cycle pulse is realized through the type-I collinear OPA with minimal temporal walk-off. The MWIR sub-cycle pulse is used for driving HHG in thin silicon samples, producing harmonics up to ~19th order with a continuous spectral coverage due to the isolated emission by the sub-cycle driver. Our demonstration offers an energy scalable and technically simple platform of laser sources generating CEP-stable sub-cycle pulses in the whole MWIR region for investigating isolated phase-sensitive strong-field interactions in solids and gases.