Generation of high-intensity KeV single-attosecond pulse using multi-cycle spatial inhomogeneous mid-infrared field

An efficient method of producing KeV single-attosecond pulses (SAPs) is proposed and investigated through the combination of a multi-cycle two-color mid-infrared field and a few-cycle near-infrared field in a metal nano-structure. It is found that by properly controlling the carrier envelope phases (CEPs) and delay time of the three-color field, not only can the quantum path of the harmonic emission be controlled, but the harmonic yield can also be enhanced by 2 orders of magnitude, leading to a high-intensity supercontinuum with contribution from only one harmonic emission event. Further, with the introduction of the inhomogeneous effect of the laser field, the harmonics emitted at the higher orders that generate SAPs occur only at one side of the region inside the nanostructure. As a result, not only can the harmonic cutoff be extended, but the modulations of the harmonics can also be decreased, showing a supercontinuum with a cutoff in the KeV region. Finally, by selecting the generated harmonics, a series of sub-35-attosecond pulses in the extreme ultraviolet (XUV) or the x-ray region can be produced. Particularly when superposing the harmonics around the cutoff region, a KeV-SAP as short as 34 attoseconds can be obtained. (C) 2018 Optical Society of America