Keitel, Christoph H. Division Prof. Dr. Christoph H. Keitel, MPI for Nuclear Physics, Max Planck Society;
http://link.aps.org/doi/10.1103/PhysRevLett.85.5082 (Publisher version)
Walser, M. W., Keitel, C. H., Scrinzi, A., & Brabec, T. (2000). High Harmonic Generation Beyond the Electric Dipole Approximation. Physical Review Letters, 85(24), 5082-5085. doi:10.1103/PhysRevLett.85.5082.