Momentum partition between constituents of exotic atoms during laser-induced tunneling ionization

The tunneling ionization of exotic atoms such as muonic hydrogen, muonium, and positronium in a strong laser field of circular polarization is investigated, taking into account the impact of the motion of the center of mass on the the tunneling ionization dynamics. The momentum partition between the ionization products is deduced. The effect of the center-of-mass motion for the momentum distribution of the ionization components is determined. The effect scales with the ratio of the electron (muon) to the atomic core masses and is nonnegligible for exotic atoms, while being insignificant for common atoms. It is shown that the electron (muon) momentum shift during the under-the-barrier motion due to the magnetically induced Lorentz force has a significant impact on the momentum distribution of the atomic core and depends on the ratio of the electron to the atomic core masses.

Figure 1

The electron distribution function over the momentum along the laser propagation direction $p_z\equiv p_{ez}/(m_{e}c{\xi }^2/2)$ in the case of a positronium ionization: (solid) via Eq. (90) using Coulomb atomic potential; (dashed) via Eq. (51) (multipled by a factor of 100) when atomic potential is modelled by a short range potential. The transverse momentum is evaluated at the maximum of the momentum distribution $p_{e\perp }=m_{e}c\xi (1+{\gamma }^2/12)$ according to Eq. (86); $p_{z,\max }\equiv {(p_{e\perp }/mc\xi )}^2+{\gamma }^2/2$ corresponds to the longitudinal component of the electron momentum at the maximum of the distribution according to Eq. (87). The laser parameters are $E_0/E_a=0.2,\omega =0.05 (\gamma =0.5,\xi =0.0172)$.