Role of resonances in the high-order harmonic enhancement in diatomic molecules

We present the study of high-order harmonic generation from the diatomic molecules produced during the laser plasma formation at the surfaces of semiconductors (InSb, InGaP, InP, GaAs). The discrepancy between the calculated molecular spectra and the observed resonance-enhanced harmonics in semiconductor molecules was attributed to the much greater influence of the strong electric field of laser radiation on the dynamical modification of the molecular spectra. The Stark shift of the energy levels of diatomic molecules was considered the main reason of the decrease of single harmonic efficiency compared to the monoatomic plasmas (In, As, Sb), where the enhancement of single harmonic was attributed to the closeness of the harmonic wavelength and the ionic transitions possessing strong oscillator strength.