We’ve been pleased by the positive reports from a number of customers using our solid metal mirrors with fibre laser sources.
At first, it seems to have been a “retrofit” emergency measure, because the original glass mirrors were found to have a very short lifetime, and then later solid metal mirrors being fitted as original equipment as they are proven “in the field”.
Often it’s been our Gold coated Copper mirrors, but our protected silver coated mirrors are being used as well.
The protected silver coating is really quite durable and withstands frequent cleaning, and it is a little more reflective than Gold in the 1 – 2um region where fiber lasers lase.
The picture we are building up points to two reasons why solid metal mirrors are being favoured over glass and quartz mirrors.
1) Laser Damage Resistance – When brand new, and when in use. Dust, dirt, and small particulate debris landing on a quartz or fused silica based mirror will cause it to crack. It’s quite possible to use several glass mirrors a day, which is of course unsustainable. It appears silicon based mirrors are just as fragile. A solid Copper mirror substrate however will sink the heat away from local absorbing “hot spots” of the dust and debris into the bulk of the mirror. It certainly won’t crack or fracture. It’s the same reason high power CO2 lasers uses copper mirrors, the high thermal conductivity of Copper sinks the heat away from local hot spots caused by dirt and debris.
2) Broad Reflective Coatings – we have had several instances where mirrors optimised for 1064nm Nd:YAG are poorly reflective to fiber laser, perhaps just 60% or so reflective.
It seems some dielectric coatings designed for 1064nm are so well optimised they have very poor performance at 1070nm, 1080nm or other fiber or disc laser wavelengths. Fiber lasers seem to have a fairly broad spectral band of operation as well, which compounds the problem.
It seems some glass mirror coatings, are compatible with some fiber laser spectral outputs, for some of the time. Not ideal for parts that will be replaced frequently.
As the debate of fiber laser versue CO2 lasers continues, Laser Beam Products can supply mirrors with the very highest laser damage thresholds for either technology.