Discrete exited states influence on the harmonics spectrum generated in two-colour laser fields

Abstract

The contribution of excited discrete atomic levels to the generation of high-and low-order harmonics in the interaction of a single atom with a two-color laser field has been studied for the first time. The studies were carried out for two types of atoms with different symmetry of the ground state wave functions (Ag, Ne) and for a two-color laser field consisting of the linearly polarized fundamental and second harmonics of Ti:Sa laser (ω + 2ω). The angle between the polarization of the ω + 2ω laser field components is varied. A significant effect of the symmetry of populated excited levels on the polarization characteristics of the generated harmonics is shown. A new method of control over the polarization state of the generated radiation is proposed.

High harmonic generation in two-color elliptical laser fields of different helicity

“…This is the origin of parity forbidden harmonics. The value of parity forbidden harmonics can be changed due to the probability amplitude dynamics of the atomic states [43]. The latter is not taken into account in the context of 'one-level' approximations, but was accounted for in the calculations of full atomic current (2).…”

Spectrum of high harmonics generated by two-color circularly polarized laser field in atomic media

“…Usually, the carrier frequency of laser pulse is smaller than the ionization potential. As a result, the excited bound atomic states influence the dynamic of atom ionization [7] and the HHG generation [8]. Hence, the width of the HHG spectrum depends on the parameters of the driving laser pulse: mainly, its intensity and carrier frequency.…”

“…Concluding, in the case of ultrashort laser pulses we can speak of the interaction of atomic electron wave packet with the laser pulse. The number of atomic states composing the wave packet depends on the laser pulse parameters [7][8][9]. The width of the response field spectrum depends on the laser field amplitude.…”