The enhancement of high-order-harmonic generation in two-color laser field in fibonacci quasicrystals

High-order harmonic generation (HHG) from the Fibonacci quasicrystal system is investigated by solving the time-dependent Schrödinger equation (TDSE). The Fibonacci quasicrystal (FQ) has a fractal structure and appears many intersections on the band structure, which may provide more possible channels for HHG than that from crystals. Our simulation shows that the electron ionization is weaker for the top valence band (VB) states than that for the states from fractal energy bands in the middle of valence bands for a two-color field scheme. This is very different for electron excitation from the one-color scheme in Fibonacci quasicrystals or crystals. Compared with the one-color field scheme, the intensity of HHG is enhanced by $3\sim 4$ orders in the case of the two-color field scheme. HHG from crystals could also be enhanced by two-color scheme, but the enhancement of the electron excitation usually comes from the states near the top of VB or resonance excitation channels. The fractal bands in FQ not only increase the ionization channels but also promote the generation of backscattering, thereby enhancing the electron distribution on the conduction band. Time-dependent population imaging (TDPI) is simulated to describe the microscopic dynamics of electrons and multiple channels from the intersection of fractal bands are proposed to explain the physical mechanism. The fractal band structure provides more sources of interference paths and may provide more information in harmonic spectra from the quasicrystal system for further investigation.