Multiphoton ionization in chaotic fields with a non-Lorentzian spectrum

The effect of the band shape of a light field on the multiphoton ionization is studied by use of the Karhunen-Loeve expansion of the Gaussian process. As an example, exact results are given for the non-Markovian chaotic field, which corresponds to a square spectrum. It is shown that the band shape of the field significantly alters ionization signals.