Desirable IR Material for Optical Applications

As NIR, SWIR, and LWIR are increasingly used for current and imminent applications such as military sighting and advancing COVID-19 testing, the optics industry has progressively used Chalcogenide glass for its highly compatible properties. This article reviews how using Chalcogenide material can be highly beneficial for lowering your cost and obtaining high performance under demanding user conditions.

Using Chalcogenide for Infrared Applications

The highly desirable qualities that belong to this group of semiconductors, in addition to the natural infrared transmission ability, include optical nonlinearity and the ability to be precision molded for custom shaping. In past years, chalcogenides were manufactured with high impurity levels, leading to performance issues and optical loss. Researchers that understood the material’s value and potential cleaned up the manufacturing process and created a family of optically pure glass that is now gaining popularity for infrared precision optics.

The many popular uses for chalcogenides occur in security, agriculture and farming, industry, inspection, and military targeting. All of these applications depend on lightweight materials that allow for high optical transmission at a low cost. 

Thermal imaging applications are increasingly in demand within the ranges of 2-5 µm and 8-12 µm. AccuCoat has been successfully supplying AR coatings on IR substrates with custom coating designs for narrower or different bandwidths up to the 15µm range.

Benefits of Using Chalcogenide Glass

Workability becomes easier and overall costs drop because of the ability to be molded, highly polished, or diamond-turned for the exact shape and dimensions required for optical assemblies. Complex lens shapes, therefore, have fewer manufacturing steps to complete. Expensive athermalization steps disappear when compared against germanium processing and coating. Optical manufacturers have begun to switch over to using this cost-effective option. If you are working with a solid optic design, using molded chalcogenide optics may reduce the lens count required in a system, further reducing the overall production cost.

Chalcogenide glass offers consistent thermal imaging performance under high heat and very low temperatures, thus avoiding the Germanium thermal drift issue.

There are numerous manufacturers for this improved family of materials that can provide a source for your next project. LightPath BD6 chalcogenide is commonly used for MWIR and LWIR thermal imaging systems, as is Schott IRG26 and Vitron IG6.

Chalcogenide is also highly compatible with high-efficiency anti-reflective (HEAR) coatings to reduce the reflected light for IR, and NIR wavelengths, which improves scattered light and optical efficiency in instrumentation.

Technical Details & Material Properties of Chalcogenide

Thermal Properties (LightPath BD6 Chalcogenide Glass)

Thermal Properties LightPath BD6 Chalcogenide Glass

Mechanical Properties (LightPath BD6 Chalcogenide Glass)
Mechanical Properties LightPath BD6 Chalcogenide Glass

When comparing chalcogenide (BD6) against germanium, here is how they stack up against each other:

chalcogenide material comparison

Optical Coating for IR Applications at AccuCoat

Not all coating houses are created equal. With AccuCoat’s strict proven process, combined with our extensive in-house optical design and coating engineering experience, we can consistently and successfully coat chalcogenide orders. Our coating capability includes specific processes for both diamond-turned or molded glass materials to fit your budget and needs. AccuCoat AR coatings for IR substrates are tested to meet Military Specifications for adhesion, abrasion, temperature, and humidity. For easy maintenance and top optical performance, AccuCoat thin-film coatings can be cleaned with alcohol, acetone, or a mild soap solution.  

Standard AR For IR Coatings Available From AccuCoat

Multilayer AR Coating (IR) – AC165

Broadband AR coating for IR
Less than 0.5% Reflection average in the region (3.5-5.0 microns)

8-12 – Multilayer AR Coating AC166
Multilayer Anti-Reflective (IR)
Less than 0.5% Reflection average in the region (8.0-12.0 microns)

Hopefully, you now appreciate how chalcogenide glass materials can be highly beneficial for lowering cost and obtaining high performance in your next demanding IR application.

Talk with our engineers before your next project to understand how AccuCoat can help with higher yields and lowering project overhead.