1. A. Kastler, J. Brossel, C. R. Acad Sci. 229, 1213 (1949).
2. J. Brossel, F. Bitter, Phys. Rev. 86, 308 (1952).
3. A. Kastler, J. de Physique 11, 255 (1950).
4. For a review of this field, see for example: E. Otten in Atomic Physics 15, H. B. van Linden van den Heuvell, J. T. M. Walraven, M. W. Reynolds eds (World Scientific, 1997).
5. See for example F. Laloë and J. Freed, Scientific American 256, April 1988, p.94