Generation of bright and Isolated Attosecond Pulses using Synchronized Ultra-Short UV and Mid-Infrared Pulses

We theoretically investigate high harmonic generation (HHG) in helium gas driven by a mid-infrared (MIR) field in combination with a delayed, high-intensity, ultrashort UV pulse as generated via resonant dispersive wave (RDW) emission in gas-filled hollow-core fibers. The UV pulse triggers low-energy electron emission through multi-photon absorption, while the long-wavelength MIR field governs the subsequent recollision dynamics. Our results demonstrate that this scheme enables the generation of bright, isolated attosecond pulses, effectively mitigating the unfavorable wavelength scaling of HHG. We explore MIR wavelengths ranging from 2 to 5 μm, examining how the delay between the MIR and UV pulses influences rescattering trajectory selectivity and the resulting HHG spectra. Our findings are supported by a semiclassical model, and we also consider macroscopic propagation effects. We also discuss potential applications of this scheme for real-time imaging techniques in molecules.