Serna Galán, JulioMartínez Herrero, María RosarioMejías Arias, Pedro Miguel2023-06-202023-06-201991-070740-323210.1364/JOSAA.8.001094https://hdl.handle.net/20.500.14352/58622© 1991 The Optical Society of America. The research leading to this paper was supported by the Empresa Nacional de Óptica, S.A. (ENOSA). J. Serna has a grant from the Programa Nacional de Formación de Personal Investigador. We also thank an anonymous referee for his suggestions for simplifying the proofs.Within the formalism of the Wigner distribution function, a new parameter is proposed, which characterizes arbitrary tridimensional partially coherent beams and is invariant through ABCD optical systems. The relationship between such a parameter and the bidimensional concept of beam quality is analyzed. An absolute lower bound that the new parameter can reach is also shown.engjournal articlehttp://www.opticsinfobase.org/josaa/abstract.cfm?id=59321open access535OpticsÓptica (Física)2209.19 Óptica Física