We present a method for calculating the spectrum emitted by an atom in an intense laser field. This method is based on the direct use of the acceleration of the atomic electron rather than the dipole moment of the atom. We show, using a numerical calculation in one dimension, that this method produces a more exact numerical evaluation of the spectrum. This technique is particularly important in determining the background to the high harmonics emitted by the atom.

• Received 9 September 1991

DOI:https://doi.org/10.1103/PhysRevA.45.3347