Role of charge-resonance states in liquid high-order harmonic generation
Chang-Long Xia, Zhengliang Li, Jiaqi Liu, Ai-Wu Zeng, Ling-Jie Lü, Xue-Bin Bian
Abstract
High-order harmonics can be generated in the gas, solid, plasma, and liquid samples driven by intense ultrafast lasers. The microscopic mechanisms of the former three have been well studied. However, liquid high-order harmonic generation (HHG) has demonstrated many unexpected results compared to other materials. Due to the complexity of liquids, it is still unknown what the quantum origin of the liquid HHG is. Here we reveal the role of localized charge-resonance states in HHG from disordered liquids. A quantum theory based on statistical two-level resonance is developed, which explains well almost all the characters of liquid harmonics known so far, such as the cutoff energy independence of wavelength. It may shed light on the optimal control of harmonic generation in liquids.