High Harmonic Generation via Cascaded Frequency-Doubling Under Sequential Active-Tuning

This study explores High Harmonic Generation (HHG) via cascaded active frequency-doubling (FD) by employing several stages of optically pumped semiconductor nanofilms. Due to their ultra-small volume, semiconductor nanofilms allow for significant tunability of the transition carrier density. Based on meticulous tuning of the optical pumping rate at each stage, the FD efficiency for an incoming laser beam can be continuously maximized via adaptive optimization of the transition electron density, which greatly enhances the effective medium nonlinearity per-stage. The strategic adjustment of the pump-rate aims to enhance nonlinear light-matter interaction sequentially, paving the way for unprecedented efficiency in HHG.