The increasing availability of sensors that can image in the 1 to 5 μm region has allowed for systems to be developed that utilize the full spectrum. Current mid-wave infrared (MWIR) systems have typically only imaged in the 3 to 5 μm region, but the new detectors allow imaging in the short-wave infrared (SWIR) and MWIR bands on the same image plane. Night Vision and Electronic Sensors Directorate (NVESD) had a requirement to design and build a multiple field of view (FOV) optical system that could image the 1 to 5 μm spectral band utilizing a single, cooled infrared detector. The primary challenge of designing this particular optical system was to get the 1 to 2 (SWIR) µm band to focus at the same image plane as the 3 to 5 (MWIR) µm band in all FOVs. A three-FOV broadband optical system that can image the 1 to 5 μm band on the same image plane was designed and built. Several optical concepts were looked at, and it was decided that a combination of a reflective afocal and refractive imager was the best way to meet the system requirements. The use of a catadioptric system with a single focal plane that images in the 1 to 5 μm spectrum reduces the size of the system and provides the user with see-spot capability.
The increasing availability of sensors that can image in the 1-5 micron region has allowed for systems to be developed
that utilize the full spectrum. Past MWIR systems have typically only imaged in the 3-5 micron region, but the new
detectors allow imaging in the SWIR and MWIR bands with the same system. The use of a single FPA reduces SWAP
and allows the user to see laser rangefinder and laser designator wavelengths. NVESD and Axsys have designed and
built a SWIR/MWIR optical system that images in the 1-5 micron band. The optical system utilizes a cooled infrared
detector that images in the 3-5 micron band as well as 1.04 - 1.08 and 1.54 microns without having to refocus the system
to see the SWIR wavelengths. This provided an optical challenge to design a system that would image from 1-5 microns
on the same detector. A combination reflective/refractive design was chosen in order to minimize packaging and meet
the different FOV requirements. This paper discusses the design and development of a multi-FOV optical system with
the capability to image across the 1-5 micron spectral band utilizing a combination of reflective and refractive
components.
Homeland security systems, special forces, unmanned aerial vehicles (UAV), and marine patrols require low cost, high
performance, multi-mode visible through infrared (VIS-IR) wavelength optical systems to identify and neutralize
potential threats that often arise at long ranges and under poor visibility conditions. Long range and wide spectral
performance requirements favor reflective optical system design solutions. The limited field of view of such designs
can be significantly enhanced by the use of catadioptric optical solutions that utilize molded or diamond point machined
VIS-IR lenses downstream from reflective objective optics. A common optical aperture that services multiple modes of
field-of-view, operating wavelength, and includes laser ranging and spotting, provides the highest utility and is most
ideal for size and weight. Such a design also often requires fast, highly aspheric, reflective, refractive, and sometimes
diffractive surfaces using high performance and aggressively light-weighted materials that demand the finest of
manufacturing technologies. Visible wavelength performance sets the bar for component optical surface irregularity on
the order of 20 nm RMS and surface finishes less than 3.0 nm RMS. Aluminum mirrors and structures can also be
precision machined to yield "snap together alignment" or limited compensation assembly approaches to reduce cost and
enhance interchangeability.
Diamond point turning, die cast and investment cast mirror substrates and structures, computerized optical polishing,
mirror replication, lens molding and other advanced manufacturing technologies can all be used to minimize the cost of
this type of optical equipment. This paper discusses the tradeoffs among materials and process selection for
catadioptric, multi-mode systems that are under development for a variety of DoD and Homeland Security applications.
Several examples are profiled to illuminate the confluence of applicable design and manufacturing technologies.
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