[1] V. Vari, R. С. Bostrom; Rev. Sci. Inst., 1968, 39, 1304.
[2] Jon Berger, R. H. Lovborg; Rev. Sci. Inst., 1969. 40, 1569.
[3] V. Gerard; J. Sci. Inst., Ser2, 1969, 2, 933.
[4] D. C. Wilson, W. R. C. Rowley; J. Sci Inst., 1966, 43, 314.
[5] K. Tanaka, T. Sakural; 1967 Sixth International Quantum Electronics Conference, Digest of Technical Papers, p48.