ИСТИНА

We study theoretically the resonant high harmonic generation (HHG) for Ga+ ion in an intense femtosecond laser field. The time-dependent Schrödinger equation was solved with expansion of the wave function over the basis set of stationary bound and up to 1200 discretized continuum states obtained numerically using the Hartree-Fock method. The obtained degree of multiphoton resonant enhancement of a single harmonic coinciding with the energy of the autoionizing state turned out to be significantly lower than in experimental observations in the plasma target. We consider the possibility of additional HHG enhancement by simultaneous exposure of the ion to much lower intense XUV radiation, which can be formed during the HHG process in plasma media. The results obtained confirm the significant increase of the harmonic intensity due to double resonance of the laser multiphoton and the single-photon XUV pumping even at relatively weaker short-wave radiation.