Optics > Interference > Thin Films DCS# 6D30.xx

COMPARISON OF LIGHT TRANSMISSION THROUGH ANTI-REFLECTION COATED AND UNCOATED WINDOWS




APPARATUS
 
two window viewers
202-21-D4
document camera
201


DESCRIPTION Each viewer contains a stack of eight 3-mm thick float glass windows separated by spacers.  One set is uncoated (reflectance is about 5%), the other has broadband multi-layer anti-reflection coatings (average reflectance ≤ 0.5%) on each face.  Pass them around or use the document camera to show the view through each.  The transmittance of a single coated window averages about 98% over the visible range, so the stack of eight windows transmits about (0.98)^8 = 85% of the incident light.  For the uncoated windows, with ~91% transmittance, the total transmittance of the stack is 47%.  This demonstrates that while the effect of the coating on a single optical element may not seem significant, the effect can be pronounced for an optical instrument with multiple elements, such as a camera lens or a telescope.

Discourage students from touching the glass.


windows