We present an alternative method for calculating energy-resolved properties from time-dependent wave functions. As a first application of the method, we calculate above-threshold ionization (ATI) spectra and energy-resolved angular distributions from hydrogen ionized by an intense, short-pulse laser at 532 nm. Below saturation the ATI peaks decrease according to an (intensity-dependent) power law. At the onset of saturation a plateau forms in the spectrum, reminiscent of plateaus seen experimentally in harmonic spectra observed during multiphoton ionization.

• Received 20 February 1990

DOI:https://doi.org/10.1103/PhysRevA.42.5794