Enhancement of strong-electromagnetic-field ionization in a constant magnetic field

Abstract

The tunneling and multiphoton ionization of a weakly bound level in an intense laser field of an arbitrary polarization and a constant uniform magnetic field, under the condition when the frequency $\ensuremath{\omega}$ of a laser field coincides with the cyclotron frequency ${\ensuremath{\omega}}_{H}$, are discussed in the quasistationary quasienergy state (QQES) formalism framework. The integral equation is derived for the complex quasienergy of the photoelectron, on the basis of the exact solution of the Schr\"odinger equation for an electron moving in an arbitrary electromagnetic wave and a constant magnetic field, obtained in Rylyuk [Phys. Rev. A 93, 053404 (2016)]. Simple analytical expressions for ionization rates in the tunneling and the multiphoton regimes by using the saddle-point method are derived and discussed. Using the ``imaginary-time'' method, the extremal subbarrier trajectory, the barrier width, and the emission angle of photoelectrons are considered. We theoretically demonstrate that when the frequency of a left polarized laser field coincides with the cyclotron frequency, the constant magnetic field does not stabilize the bound level, which leads to an enhancement of the ionization rate as compared to when the magnetic field is absent.