Impact of multichannel and multipole effects on the Cooper minimum in the high-order-harmonic spectrum of argon

We investigate the relevance of multiple-orbital and multipole effects during high-harmonic generation (HHG). The time-dependent configuration interaction singles (TDCIS) approach is used to study the impact of the detailed description of the residual electron-ion interaction on the HHG spectrum. We find that the shape and position of the Cooper minimum in the HHG spectrum of argon changes significantly whether or not interchannel interactions are taken into account. The HHG yield can be underestimated by up to 2 orders of magnitude in the energy region of 30–50 eV. We show that the argument of low ionization probability is not sufficient to justify ignoring multiple-orbital contributions. Additionally, we find the HHG yield is sensitive to the nonspherical multipole character of the electron-ion interaction.

Figure 1

The HHG spectra (a) and the depopulations of the ground state (b) of argon are compared for the intrachannel approximation (red solid line) and for the symmetrized intrachannel approximation (green dashed line). In both cases only $3p_0$ (single-channel) is active. The intensity profile of the pulse is shown in (b). The pulse parameters are as follows: $E_{\max }=0.085$, $\omega =0.057(\approx 800\mathrm{nm}),\mathrm{and}\tau =413(\approx 10\mathrm{fs})$.

Figure 2

The HHG spectra (a) and (c) and the depopulations of the ground state (b) and (d) of argon are shown for $3s$ and all $3p$ orbitals active. In (a) and (b) the interchannel and in (c) and (d) the intrachannel approximation is compared with the symmetrized intrachannel approximation. The pulse parameters are the same as in Fig. 1.

Figure 3

The HHG spectra [(a) and (c)] and the depopulations of the ground state [(b) and (d)] of argon are shown. The single-channel (only $3p_0$ active) calculation is compared with the multichannel calculation ($3s$ and all $3p$ active). No approximation [(a) and (b)] and the symmetrized intrachannel approximation [(c) and (d)] are made to the electron-ion interaction. The pulse parameters are the same as in Fig. 1.

Figure 4

The ratio of the hole populations ${\rho }_{3p_1}+{\rho }_{3p_{-1}}$ and ${\rho }_{3p_0}$ is shown for different approximations to the electron-ion interaction. The pulse parameters are the same as in Fig. 1.