1. For a general review of the field, see, e.g. J.A.R.Samson:Techniques of Vacuum Ultraviolet Spectroscopy (Wiley, New York 1967)
2. M.Seya: Sci. Light2, 8 (1952)
3. T.Namioka: Sci. Light.3, 15 (1954)
4. H.Greiner, E.Schäffer: Optik14, 263 (1957)
5. U.Gerhardt, E.Dietz: Phys. Rev. Letters26, 1477 (1971)