Multichannel High-Order Harmonic Generation from Fractal Bands in Fibonacci Quasicrystals.

High-order harmonic generation (HHG) in solids was expected to be efficient due to their high density. However, the strict transition laws in crystals restrict the number of HHG channels. Quasicrystals with fractal band structures could solve this problem and produce multichannel HHG emissions, which has been rarely studied. We simulate the Fibonacci quasicrystal (FQ) HHG for the first time and investigate the electron dynamics on the attosecond timescale. Our results reveal that (i) the acceleration theorem is approximately applicable in FQ, which provides us a valuable tool to analyze the electron trajectories. (ii) Fractal bands lead to more excitation channels, analogous to the forbidden nonvertical electron transitions in crystals. (iii) The broken symmetry results in more frequent backscattering of electrons. (iv) Compared with crystals, multichannel HHG in FQ has a higher yield and wider spectral range. Our results pave the way to understand and control the HHG in quasicrystals and shed light on a potential shorter and stronger attosecond light source based on compact solids.