1. A. Jacobsen, N. Neuroth, andF. Reitmayer,J. Amer. Ceram. Soc. 54 (1971) 186–187.
2. G. R. Newns andH. N. Daglish, Symposium on Electro-Technical Glasses, Imperial College, London, 1970.
3. A. D. Pearson, Topical Meeting on Integrated Optics-Guided Waves, Materials and Devices, Las Vegas, Nevada, 1972, Digest of Technical Papers (Optical Society of America, Washington DC, 1972).
4. D. B. Keck, P. C. Schultz, andF. Zimar,Appl. Phys. Letters 21 (1972) 215–217.
5. F. P. Kapron, D. B. Keck, andR. D. Maurer,ibid 17 (1970) 423–425.