1. T. W. Hänsch, In "Nonlinear spectroscopy", proceedings of the International school of physics, "Enrico Fermi", Course 64, Varenna, 1975, edited by N. Bloembergen, p. 17
2. H. Walther, in laser spectroscopy, edited by H. Walther (Sprinter, Berlin, 1976) p.1
3. N. Bloembergen and M. D. Lewenson, In "High Resolution Laser Spectroscopy", edited by K. Shimoda (Springer, Berlin, 1979) p.315
4. G. Grynberg and B. Cagnac, Rep. Prog. Phys., 40, 791, (1977)
5. A. Sharma, M.N. Slipchenko, M.N. Shneider, X. Wang, K.A. Rahman, A. Shashurin, Sci. Rep. 8, 2874 (2018)