What is it about?
We use thermal (infrared) cameras to look at hot objects all the time, but what happens when you try to use that camera to see a hot object on the other side of a hot window? The infrared emission from the hot window can be so bright that it blinds the camera, blocking the view of the object behind it. This article explores the best way to design coatings to reduce the infrared emission from the window while maximizing its transmissivity so the camera can see the hot object behind it.
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Why is it important?
The work presented here introduces a method for designing window coatings that work well even at very high temperatures, using with a new metric that describes how well a hot window performs. By designing coatings for both sides of the window that maximize that metric, it is found that the best strategy is to design for the highest expected window temperature. This coating design method will dramatically improve the ability of thermal cameras to see through hot windows, such as those found in manufacturing foundries and furnaces.
Perspectives
The new figure of merit and design approach introduced in this paper could be applied to a wider range of challenges beyond just temperature resiliency. Practical Coatings: The next challenges are to solve the problems of thermal expansion and angular forgiveness. Different coating materials expand at different rates when heated. It doesn’t do any good to design coatings for hot windows if the coatings peel off when heated! Likewise, it doesn’t do any good to design a coating that only works if you look straight in. The metric could be modified to guide design of practical coatings that stay attached at all temperatures and work no matter what direction the camera looks through the window. The metric could be further modified for coatings that are resilient to other environmental factors such as high pressure, humidity, or radiation. Other Wavelengths and Materials: The work presented here was designed for mid-infrared light, but the methods can be easily adapted to design coatings for other spectral regions, including the long and short wave infrared regions, the visible, or even the ultraviolet, for use in specialized optical systems or even everyday eyeglasses. These regions will require different materials and designs, so the next step will be to apply these optimization techniques to more complex or novel materials, such as metamaterials, to achieve even better performance.
Stephen Sanders
Read the Original
This page is a summary of: How clearly can an infrared detector see through a hot window?, Applied Physics Letters, July 2025, American Institute of Physics,
DOI: 10.1063/5.0266983.
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