1. Maser: Microwave Amplification by Stimulated Emission of Radiation.
2. Laser: Light Amplification by Stimulated Emission of Radiation. In some of the early literature, the laser was often called “Optical Maser”, instead. In the Soviet literature the name “Optical Quantum Generator (Okg) ” or “ Quantum Generator of Light” is sometimes used.
3. As more than 10,000 papers have been published on lasers and related topics, we refer in the present article only to those papers which were used in its preparation or which are closely related to the special topics treated. For more details the reader is referred to reference books like ToMlYasu: The Laser Literature; Ashburn: Laser Literature (Western Periodicals) or the Laser Abstracts (European Abstracts Service, Göteborg, Sweden).
4. A. L. Schawlow and C. H. Townes: Phys. Rev. 112, 1940 (1958).
5. N. G. Basov and A. M. Prokhorov: J. Exptl. Theoret. Phys. Ussr
27, 431 (1954); 28, 249 (1955).