Custom IR lenses for more challenging applications

The Infrared spectral region ranges from 0.75 to 3 µm (near-IR), through the mid-infrared (3 to 5 µm) range to the longwave-IR, or LWIR waveband (5 to 14 µm). Infrared (IR) lenses for the mid infrared waveband are well catered for by the “off the shelf” market. However, these IR lenses tend to be designed for routine applications and are not intended for use in more extreme environments.

When faced with a challenging application such as when the lens may be exposed to vibration/shock, airborne particulates or large temperature swings, it is often necessary to turn to a custom solution. For over 25 years, Resolve Optics has supplied custom Infrared (IR) lens assemblies for sensor and instrument manufacturers that seek to push the boundaries in spectroscopy, thermal imaging and materials sorting as well as pivotal applications in defence and aerospace.

Custom IR lenses for more challenging applications – Resolve Optics

To develop IR lenses for more challenging applications you are faced with choices. There is only a limited number of glass types available in that transmit well in the MWIR and LWIR wavebands. Historically the most common of these was Germanium. Aside from being expensive and increasingly difficult to source, Germanium presents a significant problem for applications subject to large temperature changes as it is particularly non thermally stable. This means that as the ambient temperature changes the glass will expand and contract forcing the lens out of focus. To enable development of athermalized IR lenses you can use selected Chalcogenide glasses which transmit well in the 8-24um range and are much more thermally stable than Germanium. Unfortunately, both chalcogenide glasses and Germanium are relatively soft and scratch easily. For applications (such as in the defence and aerospace industries) where a lens may be exposed to airborne particulates, it is important that any exposed elements should be protected with a Diamond like Carbon (DLC) coating. Although this will greatly increase the scratch resistance of the lens, in some extreme cases, it is worth considering a DLC coated window also at the front of the lens. This sacrificial front element can then be easily replaced by the end user as and when required.

Using substrates including Germanium, Sapphire, Silicon, Chalcogenide glasses and Zinc Selenide, Resolve Optics is experienced in developing and supplying IR lens assemblies with anti-reflection coatings to optimise performance in the infrared waveband to best suit your application.

To discuss development of a bespoke IR lens or optical system for a challenging application please contact Resolve Optics or visit https://www.resolveoptics.com/uv-ir-and-swir-lenses/