2 - 12 DS457-XX20004ZZWW Fixed Mount Imager Integration Guide
Window Coatings
Table 2-3 lists some exit window manufacturers and anti-reflection coaters.
Anti-Reflection Coatings
Anti-reflection coatings can be used to achieve maximum working range and to improve the range of acceptable
window positions. However, they are expensive. AR coatings also have very poor abrasion and scratch
resistance, making only single-side AR coating practical (the AR coated side of the window faces the interior of
the imager).
Polysiloxane Coating
Apply polysiloxane type coatings to plastic surfaces to improve the surface resistance to both scratch and
abrasion. Typically, you apply these by dipping, then air-drying in an oven with filtered hot air.
Table 2-1
Suggested Window Properties
Property Description
Material Clear cell-cast acrylic.
Spectral Transmission 85% minimum at 400 - 700 nm.
Thickness 0.059 ± 0.005
Wavefront Distortion (transmission) 0.2 wavelengths peak-to-valley maximum over any 0.08 in.
diameter within the clear aperture.
Clear Aperture To extend to within 0.04 in. of the edges all around.
Surface Quality 60-20 scratch/dig
Table 2-2
Taber Test Results on Common Exit Window Materials
Sample
Haze 100
cycles
Haze 500
cycles
Abrasion
Resistance
Chemically Tempered Float Glass 1.20% 1.50% Best
PMMA with Polysiloxane Hardcoat 3% 10%
ADC 5% 30%
PMMA 30% Worst
* All measurements use a 100 gram load and CS-10F abraser.
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