Highly reflecting aluminium-protected optical coatings for the vacuum-ultraviolet spectral range

We discuss the approaches to preserve the high-reflectance aluminum mirror for the vacuum-ultraviolet spectral region. Single fluoride and oxide layers, a homogeneous multilayer, and hybrid multilayer solutions are put forward. Single fluoride and oxide materials have achieved reflectance above 90% at 193 nm. Multilayer capping can provide reflectance of 93.4% at 193 nm, and a hybrid multilayer of fluoride and oxide can achieve reflectance above 90% to 160 nm.