Design of an efficient Hα filter using principles of multiple-beam interference

Abstract

The Hα emission line at 656.3 nm is a crucial spectral wavelength for studying astrophysical and solar phenomena, such as ionized hydrogen regions and chromospheres’ activity. To facilitate precise and detailed observations at this wavelength, we designed four high-performance Hα filters. These filters exhibit a full width at half maximum of approximately 1 nm or less and achieve peak transmittance exceeding 95%. Utilizing multiple beam interference based on the Fabry-Perot principle, with niobium pentoxide (Nb2 O5) and magnesium fluoride (MgF2) layers, the design ensures exceptional spectral isolation within the 625–740 nm range. This outstanding performance makes the filters highly suitable for advanced astrophysical research and solar imaging. © 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.