1. Ch.J. Bordt, M. Ouhayoun, A. VAN Lerberghe, Ch. Salomon, S. Avrillier, C.D. Cantrell and J. Bordé, in Laser Spectroscopy IV, edited by H. WALTHER and K.W. ROTHE, Springer Verlag, p. 142 (1979).
2. Ch.J. Bordé, Revue du Cethedec-Ondes et Signal NS 83–1 1 (1983) and references therein.
3. A. Clairon, A. Van Lerberghe, Ch. Breant, Ch. Salomon, G. Camy and Ch.J. Bordé, J. de Phys. Coll. 42, C8–127 (1981).
4. H. Berger, J. Physique, 38, 1371 (1977).
5. L. Henry and A. Valentin (Private communication).