1. Kazanko O.V., Penkina O.E., Golovko O.V. 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 Visnyk of V.N. Karazin Kharkiv National University, series “Radio Physics and Electronics.” 2025. № 42. C. 55-63.