1. A. A. Kaminski, Crystalline Lasers: Physical Processes and Operating Schemes, (CRC Press Inc. Boca Raton, FL 1996)
2. T. H. Maiman, Stimulated Optical Radiation in Ruby Masers, Nature, 187, 493 (1960)
3. T. H. Maiman, Optical Maser Action in Ruby, Brit. Commun. Electron., 7, 674 (1960)
4. W. Koechner, Solid-State Laser Engineering, fourth edition (Springer Berlin 1996), Sects. 2.2 and 3.6.1.
5. Ref. [4], Sects. 2.3.1. and 3.6.3.