Internal Momentum State Mapping Using High Harmonic Radiation

We numerically demonstrate so-far undescribed features in ionization and high harmonic generation from bound states with nonvanishing electronic angular momentum. The states’ modified response to a strong laser pulse can be exploited for novel measurement and pulse production schemes. It is shown that angularly asymmetric tunneling from the states can be mapped onto variations of high harmonic intensities and that near-circularly polarized isolated attosecond extreme ultraviolet or x-ray pulses can be produced.

Figure 1

Snapshots of the probability density of an electron wave packet as it is detached from a ring-current state by strong-field ionization in a linearly polarized laser field. Ionization from state (a) $|E_1⟩$, (b) $|E_2⟩$, (c) $|E_{+}⟩=1/\sqrt{2}(|E_1⟩+i|E_2⟩)$. (d) Same as (c) but for a weaker field.

Figure 2

(a) HH spectra from a ring-current state $m=+6$ for different ellipticities $\epsilon$, (b) comparison of the HH intensity in the cutoff as a function of ellipticity $\epsilon$ (dots) with the distribution of transverse electron momenta $p_{\perp }$ at the birth time for the highest harmonics (full line). Both curves were normalized to peak values of 1.

Figure 3

(a) HH spectra of $I_x$ (full red line) and $I_y$ (dashed blue line) and their relative phase (gray dots) from a ring-current state with $m=+6$. Pulse parameters as in Fig. 2 for linear laser polarization. (b) Nearly circularly polarized electric field of an attosecond pulse obtained by filtering the highest harmonics of the spectra shown in (a).