Generation of narrow-bandwidth, tunable, coherent xuv radiation using high-order harmonic generation

We theoretically demonstrate the generation of wavelength-tunable, narrow-bandwidth extreme-ultraviolet (xuv) radiation by high-order harmonic generation (HHG) driven by an orthogonally polarized two-color laser field, which is composed of a 10-fs, 1500-nm laser pulse and a 40-fs, 2400-nm laser pulse. By performing classical analysis, we reveal that the rapid change of electron wave-packet dynamics at a subcycle time scale confines high-order harmonic emission to a small spectral region, leading to the generation of narrow-bandwidth xuv radiation. Furthermore, the central wavelength of the xuv radiation can be continuously tuned over a wide range by changing either the peak intensity of the driver laser or the amplitude ratio between the two laser fields at different wavelengths. It is also verified that the use of driver pulses at longer wavelengths leads to a better spectral confinement of the xuv radiation.