1 G.. Leuchs, E.. Matthias, D.S. Elliott, S.J. Smith, and P.. Zoller, in (Sprinter-Verlag, Berlin, Interlaken, Switzerland, 1983).
1 E.. Matthias, P.. Zoller, D.S. Elliott, N.D. Piltch, S.J. Smith, and G.. Leuchs, Physical Review Letters 50, (1983).