Generation of bright and controllable isolated attosecond x-ray pulses from synchronized mid-infrared and ultrashort ultraviolet laser fields

We investigate, by solving the time-dependent Schrödinger equation in the single-active-electron approximation in helium, a two-color scheme for tabletop high-order harmonic generation (HHG) that combines a mid-infrared (MIR) driving field with an ultrashort ultraviolet (UV) pulse that could be generated via resonant dispersive wave emission in gas-filled hollow-core fibers. This configuration enables the generation of bright, isolated, and tunable attosecond X-ray pulses. In contrast to single-color driving schemes, which suffer from low conversion efficiency, unfavorable wavelength scaling, and limited spectral control, the MIR+UV approach provides a practical and controllable route for advancing tabletop ultrafast spectroscopy and real-time molecular imaging within current experimental capabilities.