Department of Mathematics2024-11-0920110375-960110.1016/j.physleta.2011.07.0522-s2.0-80052262470http://dx.doi.org/10.1016/j.physleta.2011.07.052https://hdl.handle.net/20.500.14288/10431The mathematical notion of a spectral singularity admits a physical interpretation as a zero-width resonance. It finds an optical realization as a certain type of lasing effect that occurs at the threshold gain. We explore spectral singularities of a complex spherical barrier potential and study their realization as transverse spherical electromagnetic waves emitted by a gain medium with a spherical geometry. In particular, for a typical dye laser material, we obtain a lower bound on the size of the gain medium for the occurrence of this kind of spectral singularities.PhysicsJournal Article1873-24292955008000015534