The chalcogenide glass family from SCHOTT delivers excellent transmission over wide ranges of the IR spectrum. Photo: SCHOTT/J. Stevens
Making the Invisible Visible
Through intensive R&D work and close contact with customers, the developers at SCHOTT constantly work on optimizing infrared glasses and tailoring these for use in industrial applications.
Dr. Barbara Stumpp
We cannot see infrared radiation, but we can certainly feel it as heat on the skin. Infrared (IR) or thermal radiation was scientifically proven for the first time around 1800 by the astronomer Friedrich Wilhelm Herschel. He divided sunlight into its spectral components by using a prism. Above the red, which is the longest wavelength range of visible light, he found invisible, yet warm radiation. While visible light has a wavelength of 400 nanometers (blue) to 780 nanometers (red), a distinction is made between near IR (780 nanometers to about 3 µm in wavelength), medium-wave IR (3.5 to 5 µm in wavelength) and thermal or long-wave IR (8 µm to about 14 µm in wavelength).
IR applications require high-quality optics
To make IR radiation visible, measurable and technically exploitable, whether it’s in night vision devices, thermal imaging cameras, motion control systems, pyrometers or diagnostic equipment, the optical materials used in the systems must meet very special requirements. Common soda-lime glass as well as many special glasses are opaque in the middle and thermal IR regions and are therefore unsuitable. This is caused by the absorption of IR radiation by molecular vibrations of the glass matrix (silicon-oxygen bond, etc.). Special IR glasses are perfectly usable, such as those that for years have been developed and constantly optimized in SCHOTT’s laboratories at its Duryea, Pennsylvania, site in the United States. ”Disturbing” silicon is replaced with arsenic, germanium, antimony or gallium; oxygen is replaced with sulfur, selenium or tellurium. This produces what are called chalcogenide glasses. These glasses offer the necessary excellent transmission in the short-, medium- and long-wave IR ranges, low temperature dependence on the refractive indices and low dispersion. These high-quality chalcogenide glasses can also be combined with other glasses from the series or other IR materials. ”We thus offer solutions and support optical designers in developing thermally resistant and powerful optical infrared systems,” explains Dr. Nathan Carlie, Research and Technology Development, SCHOTT North America. The optically excellent, yet sensitive glass must be separated from the operational environment by a protective window. The window must be made of a durable material that is transparent over the full operational range of the optic. For this purpose, SCHOTT scientist Dr. Keith Rozenburg has developed IRC-1, a ceramic process for producing polycrystalline zinc sulfide. IRC-1 avoids the pitfalls of zinc sulfide produced through the expensive chemical vapor deposition process.
”Our research in close proximity to manufacturing enables us to continuously optimize
Infrared Chalcogenide Glasses
Infrared Chalcogenide Glasses
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