Theoretical investigation of resonant nonperturbative high-order harmonic generation in indium vapors

Harmonic generation in laser-produced plasmas containing atoms, ions and clusters: a review

“…Some attempts at explanation of the experimental observations of resonant enhancement in plasma harmonics have been reported recently [51][52][53][54][55][56]89,90]. In particular, in [51] it has been shown that the influence of atomic auto-ionising states on the phase matching of HHG may result in efficient selection of the single harmonic in calcium plasma.…”

“…Usage of strongly ionised medium with some delocalised electrons as a target for resonant HHG can be favourable for extension of such attosecond pulse trains into the water-window region. The work of [90] was devoted to finding an explanation of the observed phenomena of resonant enhancement of a single harmonic in indium plasma without enhancement of neighbouring ones. It can also be used to predict the most promising targets for resonant HHG and to increase its efficiency by control of the pump radiation's parameters.…”

“…It can also be used to predict the most promising targets for resonant HHG and to increase its efficiency by control of the pump radiation's parameters. All computations in this work [90] were performed using the timedependent density functional theory (TDDFT) [98] with the aid of real-space real-time code OCTOPUS [99,100], which is a software package for performing Kohn-Sham TDDFT calculations. A detailed description of the TDDFT formalism can be found in [101].…”

“…In Figure 7, some of the aforementioned theoretical approaches for explanation of observed resonance enhancement of harmonics [52,89,90] are schematically compared. In Figure 7, scenario 1 shows the nonresonant three-step process, when there are no resonant states in the system; it is shown for comparison.…”

“…It is much more difficult to distinguish the approach of [90] (Figure 7, scenario 3) from that of [52] (Figure 7, scenario 4). An important physical difference between these approaches is the population of the excited state.…”