Quantum path interferences and selection in interband solid high-order harmonic generation in MgO crystals

Abstract

We theoretically investigate the quantum path interferences in interband transitions in solid high-order harmonic generation. The field strength scaling of the 19th harmonic yield from MgO crystal driven by 1600-nm lasers exhibits a sharp minimum. By solving the semiconductor Bloch equation, we separate the short and long trajectories. Our numerical calculation shows that this minimum originates from the coherent interferences between the short and long trajectories. We also illustrate that the interference minimum depends sensitively on the band dispersion, which can be used to retrieve the band structure accurately. We further report that the two-color fields can select the short or long quantum path effectively by controlling the phase. The yield at the plateau or cutoff region of the harmonic spectra can be enhanced by around one order of magnitude by adding a third harmonic with an intensity of only $10%$ of the fundamental field. Moreover, an isolated attosecond pulse (IAP) is synthesized by controlling the harmonic trajectories in the two-color scheme. The yield of this IAP is enhanced by one order of magnitude compared with the IAP generated by the single-color scheme.