Design and fabrication of narrowband 121.6nm minus filters

In imaging detection of Lyman-a line of solar spectrum, in order to maintain spectral purity, a narrowband 121.6 nm minus filter is in urgent demand. Here, first-, second-, third-order narrowband 121.6 nm minus filters are designed, fabricated, and test. We just give our initial results, and due to complexity in characterization of optical constants in 115-130 nm, there are still significant deviations between design and experimental results.