Metallic aluminum mirrors remain the best choice for high reflectance applications at ultraviolet wavelengths (90 to 320 nm) and maintain good performance through optical and infrared wavelengths. Transparent protective coatings are required to prevent the formation of an oxide layer, which severely degrades reflectance at wavelengths below 250 nm. We report on the development of atomic layer deposition (ALD) processes for thin protective films of aluminum fluoride that are viable for application at substrate temperatures . Reflectance measurements of aluminum films evaporated in ultrahigh vacuum conditions, and protected mirrors encapsulated with ALD are used to evaluate the far ultraviolet (90 to 190 nm) and near ultraviolet (190 to 320 nm) performance of both the ALD material and the underlying metal. Optical modeling is used to predict the performance of optimized structures for future astronomical mirror applications.