New Multiband IR Imaging Optics Shyam Bayya 1 , Jasbinder Sanghera 1 , Woohong Kim 1 , Daniel Gibson 1 , Erin Fleet 1 , Brandon Shaw 1 Michael Hunt 2 and Ishwar Aggarwal 3 1 Naval Research Laboratory, Code 5620, Washington, DC 2 URF, Greenbelt, MD, USA 3 Sotera Defense Solutions, Crofton, MD ABSTRACT We report new multispectral materials that transmit from 0.9 to > 12 µm in wavelength. These materials fill up the glass map for multispectral optics and vary in refractive index from 2.38 to 3.17. They show a large spread in dispersion (Abbe number) and offer some unique solutions for multispectral optics designs. One of the glasses developed is a very good candidate to replace Ge, as it has a combination of excellent properties, including high Abbe number in the LWIR, high index of 3.2, 60% lower dn/dT, and better thermal stability at working temperatures. Our results also provide a wider selection of optical materials to enable simpler achromat designs. For example, we have developed other glasses that have relatively high Abbe number in both the MWIR and LWIR regions, while our MILTRAN ceramic has low Abbe number in both regions. This makes for a very good combination of glasses and MILTRAN ceramic (analogous to crown and flint glasses in the visible) for MWIR + LWIR dual band imaging. We have designed preliminary optics for one such imager with f/2.5, 51 mm focal length and 22 degrees FOV using a spaced doublet of NRL's glass and MILTRAN ceramic. NRL's approach reduces the number of elements, weight, complexity and cost compared with the approach using traditional optics. Another important advantage of using NRL glasses in optics design is their negative or very low positive dn/dT, that makes it easier to athermalize the optical system. Keywords: SWIR, MWIR, LWIR, MILTRAN, IR glass, multispectral optics INTRODUCTION Due to developments in imaging technology and the increasing dependence on simultaneous imaging in two or more spectral bands (visible, shortwave, mid-wave and long-wave infrared) to reduce the target identification time on military platforms, there is a strong desire to develop multispectral imagers. Multispectral imagers based on reflective optics are available, but they offer narrow field of view due to obscuration and are often heavy. For military applications such as reconnaissance, search and rescue, persistent surveillance and situational awareness, wider field of view imagers are needed which typically requires refractive optics. Multispectral imaging using refractive optics could be accomplished using image fusion from multiple sensors operating in the visible (VIS), shortwave infrared (SWIR), mid-wave infrared (MWIR) and long-wave infrared (LWIR) spectral bands. These multi-aperture systems add excessive size and weight which, for payload sensitive platforms such as airborne applications (UAVs) or soldier handheld or helmet mounted imagers, the weight of the imager becomes critical. There is strong interest in developing compact, lightweight multispectral imagers using a common aperture. Recent developments in multispectral detector technology [1-3] and common focal plane arrays (FPA) can potentially enable compact imagers but are limited by development in multispectral optics. A single optical material cannot be used as a common aperture because of material dispersion, resulting in chromatic aberrations where different wavebands focus at different spots instead of on common image plane. Thus, several optical elements, of different materials, are needed to correct for chromatic aberrations over a broad wavelength spectrum [4, 5] adding size and excessive weight to the Infrared Technology and Applications XXXIX, edited by Bjørn F. Andresen, Gabor F. Fulop, Charles M. Hanson, Paul R. Norton, Proc. of SPIE Vol. 8704, 870428 · © 2013 SPIE CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2016332 Proc. of SPIE Vol. 8704 870428-1