Frequency-domain interpretation of atomic ionization in bicircular laser fields

Abstract Recently, using the laser field as a quantum field to study the interaction processes between intense lasers and matter has attracted extensive interest in the field of intense field research. In this paper, based on the frequency-domain theory where the laser field is considered as a quantum Fock state light, we have investigated the quantum coherence mechanism of the ionization spectrum in the bicircular laser fields. Using quantum channel analysis, we find that the ionization momentum spectra of atoms in the corotating two-color (CoRTC) and counter-rotating two-color (CRTC) fields are attributed to the interference between different channels, where the momentum spectra of all channels present concentric circular distribution. The crescent-shaped distribution of the total momentum spectrum in the CoRTC field is due to the phase difference between each two adjacent channels being a single azimuth angle of the ionized electron emission, while the triangular distribution of the momentum spectrum in the CRTC field is due to the phase difference between each two adjacent channels being three times the azimuth angle of the ionized electron emission. Furthermore, we employed the saddle-point approximation to analyze the interference fringes in the momentum spectrum of the CRTC field. With the help of quantum channel analysis, we give a new insight into the momentum spectrum of bicircular laser fields.