title: Comment on "Eigenfields and output beams of an unstable Bessel-Gauss resonator".
abstract: We comment on a recent paper by D. Ling et al. [Appl. Opt. 45, 4102 (2006)]. In that paper, the authors adopted the entire matrix formalism that we established in a previous work [J. Opt. Soc. Am. A 22, 1909 (2005)] for finding the eigenmodes of an unstable Bessel resonator. Nevertheless, the results are inaccurate mainly because (a) it was overlooked that light crosses through the axicon twice in a complete round trip and (b) the numerical method used to evaluate the diffraction integral equations cannot resolve the eigenvalues and eigenfields for the given resonator configuration.
authors.affiliation: Photonics and Mathematical Optics Group, Garza Sada, Monterrey, Mexico. raul.aranda@itesm.mx
authors.forename: Raul I
authors.initials: RI
authors.lastname: Hernandez-Aranda
authors.forename: Julio C
authors.initials: JC
authors.lastname: Gutiérrez-Vega