1. P. V. Avizonis, T. T. Doss, R. Heinlich, Rev. Sei. Instrument 38, 331, 1967
2. G. Nemes, M. Nemes, I. E. Teodorescu, Phase space treatment of optical beams, Proceedings of the 3rd International School of Coherent Optics, Bucharest, September 1982
3. M.V. Klein, T.E. Furtak: Optik. Berlin Heidelberg New York London Paris Tokyo: Springer 1988, pp. 457–486
4. W. A. E. Goethals, Geometrical optics of laser beams, in D.R. Hall, P.E. Jackson (eds.): The physics and technology of laser resonators. London: Adam Hilger 1989, pp. 143–153
5. M.W. Sasnett, Propagation of multimode laser beams — the M2 factor, in D.R. Hall, P.E. Jackson (eds.): The physics and technology of laser resonators. London: Adam Hilger 1989, pp. 132–142