Summary

Description

<p>Conventional high reflectance optical coatings consisting of multilayer stacks of alternating high and low refractive index dielectric materials can achieve high reflectivity and low loss over the visible to the near infra red range.  <em>Unfortunately, conventional all-dielectric interference optical coating technologies are not viable for making these components in the mid to far-infrared range due to large thick­nesses required and the lack of materials with low enough absorption at those wavelengths. </em>The task becomes even harder since the coatings typically have to operate at a cryogenic temperature: mul­tilayered dissimilar materials inevitably crack and delaminate from the substrate surface due to thermal expansion mismatch.</p>