1. Early recognition of the potential of atomic vapor laser isotope separation is generally attributed to Ambartzumian and Letokhov [Ambartzumina 1972] following their experimental work on selective photoionization of rubidium [Ambartzumian, 1971], and Levy and James [Levy, 1973]
2. R.V. Ambartzumian, V.S. Letokhov: Appl. Opt.11, 354 (1972)
3. R.V. Ambartzumian, V.N. Kalinin, V.S. Letokhov: JETP Lett.13, 217 (1971)
4. R.H. Levy, G.S. James:Method and Apparatus for the Separation of Isotopes, U.S. Patent 3,772,519 (1973)
5. For a more extensive discussion of resonant multistep photoionization, see L.J. Radziemski, R.W. Solarz, J.A. Paisner (eds.)Laser Spectroscopy and Its Applications (Dekker, New York 1987), pp. 175