Studying the effect of exchange and correlation effects on high-order harmonics

In this study, the role of multi-electron effects on the high harmonics generation by the interaction of femtosecond laser with Argon atom and N2O molecule has been investigated. First, the effect of multi-electron contribution to the generation of harmonics has been studied. It is observed that the presence of more than one electron leads to an increase in harmonics yield, especially in the cutoff region. This effect is more obvious in the systems in which their highest occupied level is degenerate. The effect of exchange and correlation interaction on the high harmonic generation is also investigated. The results showed that the effect of correlation interaction on harmonics is negligible, but the effect of exchange-correlation interaction is significant. Indeed, this remarkable influence is due to exchange interaction which constitutes 17% and 23% of the total energy of Argon atom and N2O molecule. By considering the exchange-correlation interaction for the argon atom and N2O, the harmonics yield decreased by one order of magnitude and the cutoff frequency increased by 4-5 harmonic order.