[1] L. E. Erickson, A. Szabo, Appl. Phys., 18, 433 (1971)

[2] L. G. Nair, Progress in Quantum Electronics, 7, 225 (19S2)

[3] B. Couillaud et al. in Proc. 12th IOEC, Munich Germany, 1982.

[4] F. V. Maers, T. Hebert, A. Hese, Appl. Phys., B40, 67(1986)

[5] U. Gaiiiel et al., IEEE J. Quant. Electr., QE-12, 704(1976)

[6] M. Maeda et al., Jap. J. Appl. Phys., 15, 1731 (1976)

[7] B. Couillaud et al., IEEE J. Quant. Electr., QE-20, 310(1976)

[8] P. R. Hammond; IEEE J. Quant. Electr., QE-15, 624(1970).