Photoelectron spectroscopy: A probe of the dynamics of multiphoton ionization

The dynamics of multiphoton ionization of atoms is studied through the energy and angle distributions of the photoelectrons. Experimental and theoretical results are used to elucidate the transformation in the character of the ionization process as the laser intensity becomes progressively stronger. The evolution of the spectrum is followed from the weak-field, perturbative limit to the intense field tunneling ionization regime. Dramatic changes in the laser-atom interaction are evident. Considering a simple, semi-classical picture of the behavior of the electron immediately after it enters the continuum allows a more complete understanding of the evolution of the observed distributions.