Quantitative modeling of single atom high harmonic generation.

It is shown by comparison with numerical solutions of the Schrödinger equation that the three step model (TSM) of high harmonic generation (HHG) can be improved to give a quantitatively reliable description of the process. Excellent agreement is demonstrated for the H atom and the H2(+) molecular ion. It is shown that the standard TSM heavily distorts the HHG spectra, especially of H2(+), and an explanation is presented for this behavior. Key to the improvement is the use of the Ehrenfest theorem in the TSM.