A theoretical prediction for generating isolated attosecond pulse in water window utilizing instantaneous frequency change of two-color driving laser pulse.

This work reports on the theoretical generation of isolated soft-X ray 106 attosecond pulse within the water window spectral region, through interacting a chirped two-color femtosecond laser pulse with a hydrogen atom. To construct this pulse, a chirped 3.5 optical cycle (9.33 fs) laser pulse with a wavelength of 800 nm and an intensity of [Formula: see text] is used as the main field. A 37.32 fs laser pulse with a wavelength of 1600 nm and intensity of [Formula: see text], one-quarter of the main field intensity, is employed as the control field. A tangential hyperbolic function is used to impose chirp on the main field. The study simultaneously utilizes the lowest possible intensity and the highest possible pulse duration for both the main and the control field to reach the water window spectral region in high-order harmonic generation up to the 320th harmonic of the driving field.