Quantum theory of high-harmonic generation via above-threshold ionization and stimulated recombination

A fully quantum treatment presents high-harmonic generation as explicitly a three-stage process: above-threshold ionization (ATI) is followed by continuum electron propagation in a laser field and subsequent stimulated recombination back into the initial state. The contributions of all ATI channels add up coherently. All three stages of the process are described by simple, mostly analytical expressions. Very good quantitative agreement with the previous calculations on harmonic generation by the H- ion is demonstrated, thus supplementing the conceptual significance of the theory with its practical efficiency.