The high-frequency regime

Abstract

In this chapter, we shall analyze the interaction of atoms with intense laser fields whose frequency is much larger than the threshold frequency for one-photon ionization. We begin in Section 7.1 by discussing the high-frequency Floquet theory (HFFT) within the framework of the non-relativistic theory of laser–atom interactions in the dipole approximation. In Section 7.2, the HFFT is applied to study the structure of atomic hydrogen in intense, high-frequency laser fields. An interesting prediction of the HFFT is atomic stabilization , whereby the ionization rate of an atom interacting with an intense, high-frequency laser field decreases as the laser intensity increases. This phenomenon is analyzed in Section 7.3, where we discuss ionization rates obtained within the HFFT as well as from ab initio Floquet calculations. We then consider investigations of stabilization based on the direct numerical integration of the time-dependent Schrodinger equation (TDSE). Finally, we examine the influence of non-dipole and relativistic effects on atomic stabilization. Detailed reviews of the HFFT and stabilization have been given by Gavrila [1–3]. High-frequency Floquet theory The HFFT is based on analyzing the atom–laser field interaction in the accelerated, or Kramers–Henneberger (K–H), frame [4, 5]. It was developed by Gavrila and Kaminski [6] to study electron scattering by a potential in the presence of a high-frequency laser field and generalized by Gavrila [7] to investigate the atomic structure and ionization of decaying dressed states.