Keitel, Christoph H. Division Prof. Dr. Christoph H. Keitel, MPI for Nuclear Physics, Max Planck Society;
http://link.aip.org/link/doi/10.1063/1.47506 (Publisher version)
Narducci, L. M., Keitel, C. H., Oppo, G.-L., & Scully, M. O. (1995). Subnatural linewidth in large optical fields. AIP Conference Proceedings, 328(1): 251.