Twisted elliptical multi-Gaussian Schell-model beams and their propagation properties: comment.

The inadequacy of using beam propagation factors Mx2, My2 for general astigmatic beams as those analyzed in the paper J. Opt. Soc. Am. A37, 89 (2020)JOAOD60740-323210.1364/JOSAA.37.000089 is discussed, and the appropriate beam invariants to be considered are presented.