Dressing of continuum states and MPI of Xe in a two-colour experiment

The authors report electron energy spectra resulting from MPL of Xe due to two radiation fields of different wavelengths (1064 and 307.5 nm). In addition to the well known 'above-threshold ionisation' (ATI), the authors observed the more general effect of redistribution of final states. In particular, the stimulated emission of photons-an effect which cannot be measured in a one-colour experiment-turns out to play an important role. The consequences of the observed redistribution for the interpretation of ATI are given. In addition, the authors were able to extract rather accurate information about the average intensity of the applied strong radiation field by interpreting the observed spectrum in terms of sidebands.