Intensity of Resonant Harmonic Generated in the Multiphoton Ionization Regime

The relative intensities of the resonant and nonresonant high-order harmonics, generated by singly charged gallium and indium ions in the field of a laser pulse with a duration of 20 fs and intensity ranging from 5 × 1013 to 2 × 1014 W/cm2, are calculated. The harmonic intensity is found via the matrix element of multiphoton transition within the perturbation theory including the resonant contribution. The latter increases the harmonic intensity at the transition from the ground state to the autoionizing state. We consider laser wavelength when this transition corresponds to 7 and 15 photons.