1. Topics in Applied Physics,1977
2. E. Bonek and G. Magerl, Proc. Conf. Lasers, Orlando, Florida, USA (1978).
3. V.J. Corcoran, R.E. Cupp, F.J. Gallagher and W.T. Smith, Appl. Phys. Lett.16, 316 (1970).
4. D.T. Hodges and M. Mc. Coll, Appl. Phys, Lett.30, 5 (1977).
5. J.G. Small, Physics Department, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA, Priv. Comm. (1974).