References
- Lundt , H. and Weidner , H. 1990 . Opt. Communications , 75 : 5
- Brenier , A. , Courrol , L. C. , Pedrini , C. , Madej , C. and Boulon , G. 1994 . Phys. Review , B49 : 0
- Blasse , G. and Brill , A. 1966 . Phylips Res. Repts , 21 : 368 – 378 .