Keitel, Christoph H. Division Prof. Dr. Christoph H. Keitel, MPI for Nuclear Physics, Max Planck Society;
http://www.sciencedirect.com/science/article/pii/0030401892903899 (Verlagsversion)
Fleischhauer, M., Keitel, C. H., Scully, M. O., & Su, C. (1992). Lasing without inversion and enhancement of the index of refraction via interference of incoherent pump processes. Optics Communications, 87(3), 109-114. doi:10.1016/0030-4018(92)90389-9.