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Front surface mirrors
Front surface mirrors offer excellent reflectivity over wide wavelength ranges
The term ‘front surface mirror (VS)’ can basically be applied to any mirror whose first boundary surface is a mirrored surface. In contrast to a back surface mirror (mirroring of the second boundary surface), in which the passing beam is strongly reflected at the second boundary surface and slightly reflected at the first boundary surface, the double images resulting from this beam path are avoided in a front surface mirror. The task of a mirror coating is the reflection of radiation, adjustable for the UV, VIS and IR range.
Designs of surface mirrors
Front surface mirrors are usually realised by applying metallic layers, as these have a high reflectivity over a wide wavelength range. In addition, metal mirrors whose metal layers have a rather low strength can be reinforced with additional dielectric layers. Copper is also recommended as a reflective medium for infrared diodes. The reflection values of typical front surface mirrors are between 88 % and 92 % and can also reach 94 % to 99 % for highly reflective surface mirrors. Front surface mirrors are usually designed as aluminium mirrors and are sometimes also referred to as surface mirrors.
Advantages of surface mirrors
- Double image-free image reproduction, avoidance of multiple reflections
- High reflection effect and reflection values
- By selecting different mirroring materials, different wave-dependent reflectance values can be set.
- Spectral range: UV to IR (depending on the coating material)
- Angle of incidence can be adjusted
- Substrates: Float glass, borosilicate glass, glass ceramic, quartz and metal as well as plastics (polycarbonate, COC etc.)
Application examples for front surface mirrors
- Optics, optical device construction
- Optics for sensor technology / sensor systems, e.g. positioning systems, scanner technology, barcode recognition, etc.
- Optics for beam steering (deflecting mirrors)
- Illumination optics
- Laser applications / laser technology
- Medical technology / medical devices, e.g. with ultraviolet light sources
Possible designs of front surface mirrors (examples)
- Protected aluminium mirror: Broadband surface mirror with high UV reflection and a broad reflection spectrum of approx. 200 nm - 10 µm and very good optical properties
- Enhanced aluminium mirror: Aluminium Enhanced front surface mirror with a dielectric reinforcing layer over the aluminium layer and thus improved reflection without double images (ghost image effect); large-format dimensions also possible
- Mirrors with silver coating and gold coating are also possible
- Highly reflective (HR) coating
- More about other optical coatings
- Further mirror coatings
Dielectric protective coatings
- Typically, dielectric top layers are applied to increase the durability of the mirrors and protect the metallic reflective layer.
- The reflective properties of the metallic mirror layers are not affected.
- In order to increase reflectivity in certain areas, additional dielectric layer packages can be applied (e.g. UV or IR-enhanced).
- Further information on dielectric mirror coatings
