Keitel, Christoph H. Division Prof. Dr. Christoph H. Keitel, MPI for Nuclear Physics, Max Planck Society;
http://link.aps.org/doi/10.1103/PhysRevA.53.R2933 (Verlagsversion)
Protopapas, M., Lappas, D. G., Keitel, C. H., & Knight, P. L. (1996). Recollisions, bremsstrahlung, and attosecond pulses from intense laser fields. Physical Review. A, 53(5), R2933-R2936. doi:10.1103/PhysRevA.53.R2933.