All metal mirrors are ideal for scientific instruments, they eliminate the need for mounts, and all the problems and cost that they involve. An all metal mirror like this pictured Aluminium one can have mounting holes, dowel pins, and in this case a through hole in the optical surface itself.
Aluminium mirror with Nickel coating
Our plated coatings, such as electroless nickel and gold, cover all the mirror surfaces including the internal surface of holes, so chemical resistance is maintained. With sealed CO2 lasers, these types of plated coatings are specified as they prevent the pure laser gas from being denatured by exposure to copper. I also believe, that laser gas can undermine thin film optical coatings at the copper/coating interface, causing the coating to peel or lift.
It is also possible to machine O ring grooves into the mirror if needed, both on the face, and around the circumference.
There is a small gallery of metal laser mirrors on our web site, if you are an optical engineer it may give you some idea of what is possible with all metal mirrors. Because our mirrors are chemically polished to a surface smoothness normally only available on UV grade mirrors, there are none of the diamond machining arcs, ripples, or chatter on the surface that degrade optical performance.
Laser Beam Products - Precision Optics 