Long wave infrared (LWIR) optical systems are prone to defocus with changes in temperature. IR refractive materials
are more thermally sensitive compared to conventional visible glass due to their larger therm-optic coefficients. LWIR
systems can be designed to be passively athermal (little or no change to focus with varying temperatures). Chalcogenide
glasses provide additional material choices for IR lens designers. In particular, AMTIR5 has been engineered so its
therm-optic coefficient matches the coefficient of thermal expansion (CTE) of aluminum, allowing for an athermal
singlet. This paper explores the benefits of using engineered chalcogenide glass for color corrected, passively athermal
Initially, we present color corrected and passively athermal doublets that are designed with different materials and / or
diffractive surfaces. Their thermal and color performance are cataloged for axial beams only. These are intended to be
starting components, which readers may then insert into common design forms, such as Petzval, Double Gauss,
Telephoto, and Inverse Telephoto.
A F/1.3, 20° full field of view, aspheric Petzval lens design form is explored and the MTF is evaluated for -50°C to 85°C
in an aluminum housing. From this design, we explore the tradeoffs between using chalcogenide versus crystalline
materials, diffractive versus pure refractive surfaces, and engineered chalcogenide (AMTIR5) versus "catalog" materials.