Alternative to rugate minus filters for laser eye protection

Rugate optical thin films have been studied for several decades, particularly for the application of laser eye protection filters (LEPFs). The principles of rugates and Herpin equivalent layers are briefly reviewed. The combination of these concepts to overcome the bandpass limitations of short-wave pass filters is shown. The use of Alfred Thelen's minus filters to make LEPFs is discussed, and the use of higher harmonic bands of quarter wave optical thickness (QWOT) stacks for LEPF is explained. The application of thickness ratios in layer pairs other than QWOTs is shown to lead to better alternatives for LEPF than rugates. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.