Keitel, Christoph H. Division Prof. Dr. Christoph H. Keitel, MPI for Nuclear Physics, Max Planck Society;
http://iopscience.iop.org/0953-4075/27/23/020/ (Verlagsversion)
Szymanowski, C., & Keitel, C. H. (1994). Enhancing the index of refraction under convenient conditions. Journal of Physics B: Atomic, Molecular and Optical Physics, 27(23), 5795-5812. doi:10.1088/0953-4075/27/23/020.