1. A.E. Siegman: Lasers (University Science Books, Mill Valley, CA 1986)
2. O. Svelto: Principles of Lasers, 3rd ed. (Plenum Press, New York 1989)
3. M. J.F. Digonnet (Ed.): Rare-Earth-Doped Fiber Lasers and Amplifiers, 2nd ed. (Marcel Dekker, New York 2001)
4. R. Reisfeld, M. Eyal: Possible ways of relaxations for excited states of rare earth ions in amorphous media, J. Phys. (Paris) 46, C349 (1985)
5. T. Schweizer: Rare-earth-doped gallium lanthanum sulphide glasses for mid-infrared fibre lasers, Dissertation, University of Hamburg, Germany (1998)