Metallic Coated Mirrors
Metallic
coatings are excellent broadband reflectors.
Aluminium, silver or gold may be used.
Aluminium has the broadest bandwidth extending from 200 nm to the near
IR. Silver has the highest average
reflectance and gold reflects well at longer wavelengths but cuts off at about
500 nm giving rise to its distinctive colour.
As
metal coatings are prone to oxidation, they are normally protected with a thin
layer of silicon dioxide. If a
multilayer stack is used instead of a simple dielectric layer, it is possible to
enhance the reflectance of metallic mirrors. ‘Enhanced’ metal mirrors should be selected when the
highest reflectance is required.
Substrate material is usually BK7A optical glass.
Metallic mirrors can be produced on flat or curved substrates as
required. Unless otherwise
requested we will supply them on λ/10 polished flats with a surface quality
of 10/5 or better. Metallic mirrors
are available in diameters of 10.0, 12.7, 19.1, 20.0, 25.4, 30.0, 38.1 or 50.8
mm or any custom size.