Benefits of e-nickel
Manufacturers of high powered CO2 lasers have long specified nickel plated copper mirrors for their cavity mirrors, especially in slab discharge lasers or sealed laser cavities. The reasons are:
a. Inertness to the discharge laser gas - they believe the hot laser gas discharge can react with any exposed copper and
undermine the coating at any borders/edges.
b. The copper reacts with the discharge and can contaminate the laser gas.
Inertness to cooling water
Copper in the presence of water and dissimilar metals such as steel water fittings, aluminium mounts etc., will corrode and sludge up the cooling water.
A diamond machined copper mirror (depending on its quality and the age of the cutting tool) will have visible cutting arcs and regularly spaced chatter patterns on the face. Along with this though is the crystalline structure of the copper. The surface grains of copper are typically a few hundred microns in size and give the mirror surface a crazed or granular appearance. Laser damage occurs when these individual grains break away from each other (in the same way a crazy paving stone can break away from the rest). Electroless nickel is amorphous, it has no crystalline grain structure so the polished surfaces are smoother and withstand higher laser powers.
Ease of cleaning/preparing for coating
Bare copper mirrors soak up contamination from the environment and will easily stain. Physically touching the copper will cause scratches. Electroless nickel will remain unchanged for months and although we do vacuum pack mirrors, it’s not strictly necessary. Also, nickel can be cleaned with solvent/tissue (we prefer cotton wool) quite robustly without scratching.