Abstract

Above threshold ionization is one of the fundamental new phenomena revealed in the study of atoms in very intense light fields ( > 10¹³ W/cm²). ATI is the production of photoelectrons at a number of discrete energies above the ionization limit. The electron energies appear to closely follow the relation E =(Nħw–E_ionizanon)+Sħω; that is, they correspond to absorption of an additional S photons more than the minimum number N needed to ionize the neutral atom or molecule. Understanding ATI is essential to determining the role of coherent and incoherent processes when the radiation field forces become comparable to atomic forces. The work reported here supports the interpretation of ATI as a coherent rather than a stepwise process.

© 1986 Optical Society of America