Navy

Optical material for short- and mid-wave infrared imaging

A new class of synthetic inorganic-organic polymeric materials to fill a void in MWIR and SWIR ranges

Materials

By Bnikolov (Own work)

Infrared (IR) optical technology has numerous potential applications in civil, medical, and military areas, where inorganic semiconductors and chalcogenide (one electropositive element plus one group 16 element such as sulfur, selenium, tellurium) glasses have been widely used as materials for IR device components, due to their high refractive index and low optical losses. While such materials are well suited for these applications, they are inherently more expensive and difficult to process – due to the high processing temperatures and volatile nature of the compounds in comparison to organic polymeric materials. Still, polymers are desirable due to their light weight, low cost, and ease of processing into optical components. However, the development of polymeric materials for short-wave infrared (SWIR) and mid-wave infrared (MWIR) optical applications has not been achieved due to challenges in designing systems with sufficiently high refractive index and transparency in the infrared spectral region.

Refractive index and dispersion dictate the shape and size of lenses, and higher values are needed for better focusing power and wave-guiding of light. The most common way to increase the refractive index of an organic polymer is by the incorporation of highly polarizable elements, such as sulfur, selenium, and tellurium.  Researchers have previously been able to incorporate sulfur into an organic polymer, but the technique has failed with selenium and other group 16 elements.  However, Navy researchers have recently developed a method to make a polymer with a crystalline selenium-sulfur blend, yielding a refractive index higher than conventional polymers and low absorption losses in the IR region. This chalcogenide-based polymer comprises a backbone of sulfur and selenium (or tellurium) crosslinked with functional groups like divinylic moieties that can also crosslink to create a stable polymer.

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