2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/85414A spherical Fabry-Perot interferometer with adjustable mirror spacing is used to produce interference fringes with frequency separation (c/2L)/N, N=2-15. The conditions for observation of these fringes are derived from the consideration of the eigenmodes of the cavity with high transverse indices.11 pages, 7 figures, accepted to Siberian Journal of PhysicsAtomic PhysicsOpticstext