1. Some review articles on optical pumping: J. Brossel, Quantum Optics and Electronics Les Houches Summer School, 1964, p. 187 ( Gordon and Breach, New York, 1964 )
2. C. Cohen-Tannoudji and A. Kastler, Progress in Optics (North Holland, Amsterdam, 1966 ), vol 5, p. 1
3. A. Kastler, Science 158, 214 (1967)
4. G.W. Series, Quantum Optics (edited by S.M. Kay and A. Maitland) p. 395, Academic Press, 1970
5. W. Happer, Rev. Mod. Phys. 44, 169 (1972)