Serna Galán, JulioMovilla Serrano, Jesús María2023-06-202023-06-202001-04-010146-959210.1364/OL.26.000405https://hdl.handle.net/20.500.14352/58587© 2001 The Optical Society of America. We thank G. Piquero and G. Nemes for helpful discussions. This study was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain under project PB97-0295.The definition of the orbital angular momentum established for coherent beams is extended to partially coherent beams, expressed in terms of two elements of the beam matrix. This extension is justified by use of the Mercer expansion of partially coherent fields. General Gauss-Schell-model fields are considered, and the relation between the twist; parameter and the orbital angular momentum is analyzed. © 2001 Optical Society of America.engjournal articlehttp://www.opticsinfobase.org/ol/abstract.cfm?id=63848open access535Light-BeamsÓptica (Física)2209.19 Óptica Física