High spectral purity at longer wavelength side is demanded in many extreme ultraviolet (EUV) and soft X-ray (together also referred to as XUV) optical systems. It is usually obtained at the expense of a high loss of XUV efficiency. We proposed and developed a new method based on a periodic, tapered structure integrated with an EUV multilayer. The longer wavelength radiation is scattered/diffracted away by the tapered multilayer structure while the EUV light is reflected. The first proof-of-principle showed a broadband suppression from λ = 100-400 nm with an average factor of 14. Moreover, a high EUV reflectance of 64.7% was achieved, which corresponds to 94% of the efficiency of a regular EUV multilayer mirror.
Huang, Q., de Boer, M., Barreaux, J., van der Meer, R., Louis, E., & Bijkerk, F. (2014). High efficiency structures EUV multilayer mirror for spectral filtering of long wavelengths. Optics express, 22(16), 19365-19374. https://doi.org/10.1364/OE.22.019365