1. E.J. Woodbury and W.K. Ng, Proc. IRE, 50, 2347 (1962):
2. G. Eckhardt, R.W. Hellwarth, F.J. McClung, S.E. Schwarz, D. Weiner, and E.J. Woodbury, Phys. Rev. Lett., 9, 455 (1962).
3. B.P. Stoicheff, in Proc. International School of Physics “Enrico Fermi”, Course XXXI, 1963, C.H. Townes and P.A. Miles, eds., Academic Press, New York, pp. 306–325 (1964)
4. B.P. Stoicheff, Phys. Lett. 7 ,186 (1963).
5. R.W. Minck, R.W. Terhune, and W.G. Rado, Ap. Phys. Lett., 3, 181 (1963).