Material selection for color correction in the short-wave infrared

Abstract

With the increasing availability of InGaAs detectors for imaging applications in the short wave infrared (SWIR, 0.9 - 1.7 μm), the need for diffraction limited lenses optimized for this spectrum is rising as well. With an abundance of commercially available optical glasses that are transparent in the SWIR, correcting chromatic aberration over the broader SWIR waveband might seem only a moderately difficult task for the optical designer. As it turns out, it is considerably more difficult because the dispersive nature of most of the common glass flints is decreased in the SWIR, limiting the availability of strong flints for achromatization. Fortunately, a limited selection of highly dispersive SWIR transparent materials can be found among materials used for mid-wave and long wave infrared (IR) optics. However, some of these IR materials have a strong absorption edge in close proximity to the SWIR waveband which presents the optical designer with a different challenge. This paper examines challenges and tradeoffs specific to material selection for color correction in the design of diffraction limited lenses for the SWIR. Solutions are proposed for achromatic and apochromatic lenses. A discussion of material properties and the SWIR glass map is included.