1. E. Spiller,J. Appl. Phys. 43 (1972) 1673.
2. Y. Mitsuhashi, Paper presented at the Symposium on New Measurement Techniques, Sapporo (1974).
3. V. Blažek,Optics Commun. 11 (1974) 144.
4. D. Gabor,Progress in Optics, Vol. 1, North-Holland (1961).
5. N. G. Basov et al., Kvantovaja Radiofizika 31 (1965) 74 (in Russian).