1. R. Brown and R. Twiss, “A Test of a New Type of Stellar Interferometer on Sirius,” Nature 178, 1046 (1956).
2. V. A. Fabrikant, “On the Problem of an Experimental Proof of the Existence of Negative Absorption,” Tr. VEI 41, 273 (1940).
3. M. Bertolotti, “Why Was the Laser Invented So Late?” Newsletter ICO, No. 82 (2010).
4. N. G. Basov, B. M. Vul, and Yu. M. Popov, “Quantum-Mechanical Semiconductor Generators and Amplifiers of Electromagnetic Oscillations,” ZhETF 37, 587 (1959).
5. N. G. Basov, O. N. Krokhin, and Yu. M. Popov, “Obtaining Negative-Temperature States in p-n Junctions of Degenerate Semiconductors,” ZhETF 40, 1879 (1961).