Case Study: Dichroic Filters for separation in 3-5µm Infra -Red Range

Case Study: Beamsplitter for separating IR gas absorption bands in the Mid IR

Customer Challenge: In gas analysis instruments, many gases have a strong IR absorption band, and these can be quite close together spectrally. A customer asked us to manufacture a steep edged dichroic filter to ensure separation of 2 such spectral regions.

Vortex’s Solution: We quickly produced a custom design for the customer to study. During the subsequent discussions two other points emerged. Firstly, the filter could see a wide range in temperature, maybe as much as 120°C, so stability was important, our state-of-the-art sputtering process was essential for this requirement.  The filter would just not work if deposited using conventional thermal evaporation technology as the thermal shift of these coatings is too high. Secondly, the gas molecules could hit the filter at a wider range of angles than initially expected, this necessitated making the filter edge steeper to ensure no crosstalk from other gases likely to be present.

The Result: The spectral performance for T and R at 45° angle of incidence are shown in the spectral graph, the filter also passed a series of Mil spec type tests such as adhesion, abrasion, chemical exposure and humidity to ensure it was suitable for the aggressive environment it would encounter.