Installation 2 - 13

Window Coatings

Table 2-3 on page 2-14 lists some exit window manufacturers and anti-reflection coaters.

Anti-Reflection Coatings

Apply an anti-reflection coating to the inside and/or outside of the window to significantly reduce the amount of light
reflected off the window, back into the scan engine. The coating can also improve the range of acceptable window
positions and minimize performance degradation due to signal loss as the light passes through the window. Using
anti-reflection coatings on both the inside and outside of the window is highly recommended.

Polysiloxane Coating

Polysiloxane type coatings are applied to plastic surfaces to improve the surface resistance to both scratch and
abrasion. They are usually applied by dipping, then air-drying in an oven with filtered hot air.
Table 2-2
Suggested Window Properties
Property Description
Material Red cell-cast acrylic.
Spectral Transmission 85% minimum from 640 to 690 nanometers.
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
Coating Both sides to be anti-reflection coated to provide 0.5% max reflectivity
(each side) from 640 to 690 nanometers at nominal window tilt angle.
Coatings must comply with the hardness adherence requirements of
MIL-M-13508.