Coherent control of multiphoton resonance dynamics in high-order-harmonic generation driven by two frequency-comb fields

摘要

We present a theoretical investigation of the multiphoton resonance dynamics in the high-order-harmonic generation (HHG) process driven by two frequency-comb fields with the carrier frequencies of fundamental and second harmonics, respectively. The many-mode Floquet theorem is employed to provide a nonperturbative and exact treatment of the interaction between a quantum system and frequency-comb laser fields. The coupling of the weak second-harmonic control frequency-comb laser field promises more routes to coherently optimize the multiphoton resonance dynamics and HHG power spectra. First, even-order harmonics are generated due to the coupling of the second-harmonic frequency-comb field. Second, the HHG power spectra can be greatly enhanced via multiphoton resonance, which can be achieved by tuning the carrier-envelope-phase (CEP) shifts and the peak intensities of both frequency-comb fields. Furthermore, besides the multiphoton transitions involving only fundamental-harmonic photons, additional multiphoton transitions involving both fundamental-and second-harmonic photons occur, resulting in the generation of combs with frequencies dependent on CEP shifts of both fields. Different multiphoton transition paths can interfere with each other when the two CEP shifts are matching, and the interference of paths allows one to coherently control the HHG power spectra by varying the relative phase between the fields.