Solid aluminium mirror substrates can be used with all but the most powerful lasers. In the example below the pyramidal mirror has been electrochemically gold coated. The gold coating covers the vertices and the faces in one continuous layer that will never peel or flake.
In the base are an array of tapped holes for mounting and alignment. We made just two of these parts very cost effectively for prototyping. Chemical polishing gives low scatter mirrors suitable for UV use, with surface roughness far superior to SPDT mirrors.