1 W.J. Alford, N.. Andersen, M.. Belsley, J.. Cooper, D.M. Warrington, and K.. Burnett, Physical Review A 31, (1985).
1 M.W. Hamilton, W.J. Sandle, J.. Chilwell, J.. Satchell, and D.M. Warrington, Optics Communications 48, (1983).
1 R.J. Ballagh, J.. Cooper, M.W. Hamilton, W.J. Sandle, and D.M. Warrington, Optics Communications 37, (1981).