Although there is ongoing work exploring new materials that have high reflectivity at longer EUV wavelengths (i.e. ~ 500Å–700Å), at present there is a lack of suitable narrowband multilayer for wavelengths greater than 500Å.

It is hoped that eventually, tunable narrowband multilayers in this region will be possible. If that is the case, other dual line options above 500 Å become possible. These wave also be included under the wavelength options.