Concave Spherical Mirrors
Spherical
mirrors are used to collect and concentrate light at a point.
They have a focal length equal to half their radius of curvature.
Either BK7 or fused silica mirror substrates used and these are made to
laser standards (λ/10, 10/5).
A
variety of reflective coatings may be applied.
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.
Concave
spherical mirrors are available in diameters of 12.7, 19.1, 25.4, 38.1 or 50.8
mm or any custom size.
The radius of curvature may be selected from the following range: 25, 50, 75, 100, 150, 200, 250, 300, 400, 500, 750, 1000 mm. Please ask if you need a different radius of curvature as these can be made to special order.