Antireflective Coatings
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Dontech offers a variety of vacuum deposited
antireflective (VAR) optical coatings for reducing specular reflections
from the surfaces of optical substrates. VAR coatings are used
in applications where very high ambient light readability is required,
such as in avionic cockpit displays. They are also used when antireflection
properties are required without any degradation to the resolution
of the transmitted image. VAR coatings accomplish reflection reduction
by converting reflected energy into transmitted light.
Dontech's standard VAR coatings are designed around the photopic
response of the human eye; hence, coatings are tuned for the spectral
region of 425 nm to 675 nm (i.e., the dominate portion of the
visible daylight spectrum). Exact performance specifications are
both wavelength and angle based. Typically these coatings are
comprised of three or more thin layers or stacks of dielectric
and conductive transparent oxide materials, which are applied
using high vacuum evaporation or sputtering processes. The specific
coating process and configuration will vary with the desired level
of performance, substrate and hard coating (if any). The deposited
materials for coatings are selected based on index of refraction,
spectral transmission, conductivity, durability, cost and required
coating temperature. Higher performance coatings may be achieved
by integrating more layers into the optical stack; however, the
increase in performance will quickly become very small especially
when compared with the increase in coating costs.
Dontech offers several varieties of vacuum deposited antireflective
coatings. Common industry specifications are as follows:
• SAE AMS-2521
• MIL-C-675
These coatings include VAR-0.25, VAR-0.5, and
VAR-0.75. The name indicates the average maximum percentage photopic
specular surface reflection for normal incident white light (i.e.,
VAR-0.25 has a maximum total luminous reflection of illuminant
D65 of 0.25% maximum). Dontech can design custom vacuum deposited
coatings to satisfy special requirements.
Dontech application engineers can recommend
the antireflective coating best suited for your application. For
additional information on antireflective coatings, please contact
a Dontech applications engineer, or request that a hard copy of
the Windows Design Guide be sent to you.
