“Development of a methodology for transitioning from a spectral equation relative to a spatial variable to a differential equation relative to a spectral parameter in the Sturm-Liouville problem for a one-dimensional periodic two-layer photonic crystal” (2025) Visnyk of V.N. Karazin Kharkiv National University, series “Radio Physics and Electronics”, (42), pp. 55–63. doi:10.26565/2311-0872-2025-42-06.