Tunneling ionization of atomic hydrogen by an intense low-frequency field

Abstract

We present results of Floquet calculations of rates for ionization of H by high-intensity light with wavelengths up to 1064 nm. If the frequency \ensuremath{\omega} is well below the atomic-orbital frequency ${\mathrm{\ensuremath{\omega}}}_{\mathrm{at}}$ the rates approximately obey a law similar to that given by the Keldysh tunneling theory, and they approach the dc rate as the intensity increases. If \ensuremath{\omega}>${\mathrm{\ensuremath{\omega}}}_{\mathrm{at}}$ there is no tunneling regime and the rates eventually decrease toward zero as the intensity increases.