Photoionization of the hydrogen atom in an intense high-frequency field: the two-pole approximation

High-frequency Floquet theory (HFFT) is again applied to photoionization in a linearly polarized field of the hydrogen atom in its ground state. The n ew feature is the systematic use of a two-pole approximation to represent b oth the dressed potential (with two positive charges) and the coupling resp onsible for one-photon ionization (with two charges of opposite sign). With in such a scheme, both the initial bound and the final continuum states can be very accurately determined. The final continuum state is obtained by de riving, from Floquet theory, an equation involving a source term. The model accounts reasonably well, even at rather low frequencies, for the stabiliz ation of the atom in an intense held and supports the claim that HFFT repre sents the photoionization rate with a golden rule expression involving dres sed stales.