Infrared windows are used to protect optical components from environmental influences while ensuring high transmission. They are typically used in front of thermal imaging cameras to protect the lenses or in front of pyrometers to prevent corrosive particles from entering and damaging the electronics.
Infrared windows are also frequently used in detectors to hermetically seal CMOS circuits, as these require a low-pressure environment for operation.
Silicon substrates are typically used for the mid-infrared range (MWIR) and germanium for the long-wave infrared range (LWIR). However, due to their high refractive indices of 3.4 and 4, respectively, an anti-reflective coating is usually required. However, this is not without its problems. It can peel off at fluctuating temperatures, produces a strong angle dependence, and is sensitive to corrosive materials or in a salty environment. One solution is to additionally coat the window with DLC (diamond-like carbon), a material with mechanical properties that make it slightly more resistant. However, this makes the product more expensive and still does not offer a complete solution.
Mapsi Photonics is taking a different approach, based on the principle of “less is more.” Instead of applying layers of different materials to a substrate, they texture silicon using a chemical process that offers significant time and cost savings compared to the use of multiple layers. In addition, Mapsi avoids the use of exotic materials of high geostrategic relevance. Their import can be subject to political fluctuations and have social and environmental impacts in the countries where they are produced. The mechanical properties of silicon, which are even far superior to those of DLC, are retained and the optical properties are improved.
In SWIR and MWIR, Mapsi windows achieve up to 97% transmission. The T-curve is flat over a wide range and does not exhibit any valleys or peaks, as is common with multilayer windows. In the LWIR range, the spectral sensitivity is slightly lower than that of germanium. However, the potential unavailability of the material (germanium is currently subject to severe export restrictions) and the significantly lower price compared to other options are strong arguments in favor of Mapsi windows in this wavelength range as well.
In summary, Mapsi BBARs are of high optical quality, ideally suited for corrosive environments, very cost-efficient, and have a much lower environmental footprint. 
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