Coating of metals like aluminum / silver / gold on the polished glass surface increases the reflection and are useful for many applications. These metals characteristically exhibit high reflection over very broad wavelength regions.
coated mirrors are very stable and most commonly used since aluminum gives reflection right from UV to IR region.
Aluminum mirrors to be used in the visible region are usually protected with a layer of Silicon Monoxide for durability. To increase the efficiency of the coating and to make it even more durable, enhanced aluminum mirrors are available for visible region which have multiple dielectric layers on top of the aluminum to boost the reflection.
UV aluminum mirrors are those which have high reflection even in the UV region. These normally have a soft protective layer on top of the aluminium coating, just to prevent the oxidation of aluminium.
has the highest reflection in the visible region but is more expensive due to the difficulties involved in the coating process. The coatings are not as stable as aluminum. We give protected silver coatings which are as durable as aluminium coatings.
can be used for reflection in IR region.
Dielectric coatings are used when higher reflection and durability is required as compared to metal coatings. These can be tuned for wavelengths from UV to IR region and for specific angle of incidence.
Dielectric coatings can also be tuned to get partial reflection. These are normally used at normal incidence. and may have an anti-reflection coating on the second surface.