Electron dynamics in the strong field limit of photoionization

Abstract

The behavior of atoms in strong fields has been the subject of many investigations, both experimental and theoretical. Previously, the majority of experimental studies have been confined to the multi-photon ionization or mixed regimes while few experiments have been done in the tunneling regime[1,2]. The data we will present is the first to examine the photoionization process over the intensity range from multiphoton ionization to well within the tunneling regime. We have taken photoelectron energy spectra, ion yield curves, and angular distributions of helium and neon over a wide range of intensities using a titanium sapphire laser operating at 1 kHz, 780 nm, and a pulse width of ~120 fs, focused into an UHV chamber with f/4 optics, allowing maximum intensities of 20 PW/cm2. The large dynamic range allowed by the kilohertz repetition rate makes it possible for a quantitative comparison between experiment and theory. Helium and neon were chosen for the study since previous investigations have established that ionization occurs in the tunneling regime [3]. Our investigations show that while the rescattering model [4,5] describes the one electron dynamics quantitatively, the extension of the rescattering model to inelastic rescattering as a mechanism for creating higher charge states fails to provide even a qualitative description.

Hot electrons in the tunnelling ionization of atoms

“…In fact, on a logarithmic scale, the electron spectrum at high energies consists of an extended plateau. The recent measurements of Sheehy et al [1] and Walker et al [2] for helium at around 10 15 W cm −2 do reach up to electron energies exceeding 10U p (where U p is the ponderomotive energy of the electron), i.e. the classical cut-off of the electron energy spectrum due to rescattering [3].…”

“…The ionization rate can again be calculated according to equation (1). But in the case of backscattering we have two classical complex turning points t 0 : the first corresponds to electron velocity, equation (11), while the second corresponds to electron velocity, equation (2).…”

Rescattering of Photoelectrons in the Tunneling Ionization of Atoms by Strong Laser Radiation

“…Last measurements reported in Refs. [1][2] for helium atom at 10 15 W/cm 2 show that a plateau in the electron energy spectrum occurs beginning from 1.5-2 ponderomotive energies up to cut o¡ (about of 10 ponderomotive energies for backscattering, see Ref. [3]).…”