This PDF file contains the front matter associated with SPIE Proceedings Volume 10998, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

ORganically MOdified CHALCogenide (ORMOCHALC) polymers are novel materials that can be synthesized through the recently discovered inverse vulcanization process. Inverse vulcanization requires the heating of chalcogenide comonomers along with compounds that contain available pi electrons. The composition of the polymers presented includes the use of previously unexplored multi-vinyl branching agents, as well as polymer backbones that contain selenium. The crosslinking by unique comonomer species, and the use of selenium as a backbone component are significant in that they have a direct and pronounced effect on the optical properties of the polymers produced. Specific optical benefits of ORMOCHALC polymers include the extensive infrared transmission profile and the unusually high refractive indices these polymers possess. We present the synthesis and optical characterization of unique ORMOCHALC polymers.

One of the difficulties in designing infrared optical systems is the comparative lack of glasses from which to design lenses. In visible optical systems, the designer has a palette of hundreds of glass options with varying dispersions and mechanical properties. In contrast, the designer of infrared optical systems has perhaps a dozen materials options from which to choose. Instead, what if the infrared transparent materials were designed specifically for various applications? Using a material with a targeted index dispersion profile, the designer can complete a system using fewer lens surfaces and in many cases with increased functionality such as athermalization. Next comes the question of how to obtain such a material. One approach is somewhat scattershot: to melt series of glasses, measure each of their properties, and settle on one composition for scale-up to production volumes. This approach is both time- and resource-consuming, as the measurements for many properties require specialized equipment and sample preparation. In contrast to this scattershot method, the principle of intelligent material design allows glass scientists to design glasses with intentionally chosen mechanical and optical properties, and greatly reduces the number of test melts required to obtain a final production solution. Intelligent material design consists of leveraging the existing literature data to make informed decisions about which glass compositions are likely to exhibit the desired properties. By describing the variation of the properties over the glass family with mathematical functions, the material design problem is reduced to the simultaneous solution of a set of equations.

Optical design requires an accurate knowledge of the dispersion functions for the materials in each lens. For systems to work over a wide range of temperature, knowing the temperature dependence of these functions is as important as knowing the coefficients of thermal expansion. The dispersion curves of several NRL-developed infrared glasses were measured over a temperature range that spanned, at minimum, -20°C to 60°C. Details concerning the data fidelity, data modeling, fit results, and physical implications of the results will be provided in this work.

Due to changes in the fictive temperature as a result of the precision glass molding process there is an induced change in the index of refraction. This can be on the order of 0.001 in oxide glasses and as high as 0.02 in the chalcogenide glasses. It is important to accurately define the expected index of refraction and the tolerance of it after molding as there may be an impact on the optical design tolerances and system performance. We report on the measured change in index of refraction in common chalcogenide glasses due to the Rochester Precision Optics (RPO) precision glass molding process. We will compare the change in index of refraction between as advertised, as measured, as molded, and we will look at post mold annealing recovery. Utilizing an upgraded M3 refractometer we will be able to measure the index from the visible to the LWIR.

Chalcogenide glasses have been steadily advancing infrared imaging capabilities and systems since the mid 1900s. Rochester Precision Optics has recently invested in bolstering their infrared glass manufacturing capabilities. While vertically integrating to reduce costs and to support the current and expanding demand for their precision glass molding, diamond turning, and assemblies that use the classic chalcogenide glasses; the optical design team has been able to capitalize on the new infrared materials further expanding the infrared optical glass map for S.W.A.P. enhancement in their designs. The focus of this work is to highlight some of the capabilities and recent innovations in chalcogenide glass manufacturing leading to low cost methods of producing optical materials, elements, unique or previously difficult geometries.

As next-generation space-based telescopes require larger mirrors, replicated composite optics are gaining increased attention due to limitations in scalability of conventional glass optics. Replication is the process of transferring an optical surface to a thin polymeric film supported by a CFRP substrate, offering weight savings, cost reductions, and faster manufacturing times. These optical surfaces require both dimensional precision (RMS < 32nm) and dimensional stability in a variety of environments. In our previous work, high quality replications were fabricated with UV-cured epoxy resin. Our work showed that the class of resin material as well as the processing route chosen had significant effects on the final stability of the composite optic. However, the fundamental material properties governing the behavior are not yet fully understood. In this paper, we will investigate how varying amounts of photoinitiator concentration on a UV-cured epoxy affect inherent material properties. The influence of these properties on the hygroscopic stability of the resin will be discussed.

New missions and technical systems require lightweight, high performance, wide-field of view (W-FOV) infrared (IR) imaging systems. Traditionally, multilayer antireflective (AR) coatings are utilized with optical components to facilitate these high performance demands. However, fundamental limits in these multilayer AR coatings currently prevent the extremely high broadband transmission (<95%) and W-FOV (<100°) requirements of next generation IR imaging systems from being realized. Furthermore, there is restricted availability of suitable thin film IR materials with high index contract used in these AR coatings, preventing tuning and broad application of the technology. By contrast, surface-engineered gradient reflective index (GRIN) films afford a substrate and application independent means of generating and tuning transmissive and W-FOV properties in optical components. Herein, we present efforts toward designing devices with highly AR properties from GRIN surfaces. GRIN surfaces are generated through lithographic patterning of optical surfaces and dry etching processes to generate dense arrays of air holes. The density of these air holes offer a mean to tune the index of refraction of the optical surface, providing highly AR properties in a tunable optical range. State-of-the-art laser writing technology enables us to achieve features of 500 nm and below with high throughput (<1.25 min write time per 1 cm² patterned). Control of depth etch through standard etching processes (Al₂O₃ hard mask, deep etch using Bosch-process type or other dry etch) allows for fully tunable GRIN films.

New moldable, infrared (IR) transmitting glasses from NRL and graded index (GRIN) optical materials enable simultaneous imaging across multiple wavebands including SWIR, MWIR and LWIR and offer potential for both weight savings and increased performance in optical sensors. Lens designs show the potential for significant SWaP reduction benefits and improved performance using NRL materials and IR-GRIN lens elements in multiband sensors.

We demonstrate a scalable photo-thermal process which enables manufacturing of infrared (IR) transmissive glass-ceramic films with gradient refractive index (GRIN) profiles. Spatiallycontrolled laser irradiation creates Pb-rich amorphous phases within Ge-As-Pb-Se glass films, which are subsequently crystallized and become high index phases upon heat treatment. The density of the high index nanocrystals is shown to be controlled by the laser irradiation power, and the extent of fraction crystallized is controlled by post heat treatment time and temperature. Both of these variables can be optimized to realize a localized effective refractive index change, enabling a spatially-modulated refractive index change up to ~ +0.1. We demonstrate IR GRIN functionality within 1 inch diameter GAP-Se films with thicknesses ranging from 1 to 40 μm, confirming the scalability of our photo-thermal process to component-relevant geometries.

The mid-wave infrared (MWIR) is an important band for numerous applications ranging from night vision to biochemical sensing. However, unlike visible or near-infrared (NIR) optical parts, which are economically available off the shelf, MWIR optics are plagued by much higher costs and often inferior performance compared to their visible or NIR counterparts. Optical metasurfaces, artificial materials with subwavelength-scale thicknesses and on-demand electromagnetic responses, provide a promising solution for cost-effective, high-performance infrared optics. Using high-refractive-index (> 5) chalcogenide materials deposited on IR-transparent substrates, we have experimentally demonstrated a MWIR transmissive metasurface device with diffraction-limited focusing and imaging performance and optical efficiency up to 75%. We further show that the metasurface design can accommodate ultra-wide field-of-view and the fabrication method can be extended to conformal integration of metasurface optics on curved surfaces. The projected size, weight and power advantages, coupled with the manufacturing scalability leveraging standard microfabrication technologies, makes the meta-optical devices promising for next-generation MWIR system applications.

Plasmonic materials offer the extraordinary property of optical field confinement, and find emerging applications in sensing, optical computing, sub-wavelength imaging among others. Developers wishing to exploit this phenomenon however, are limited by the sparse availability of reliable, experimentally-derived optical constant data (n & k) for the purposes of optical simulations. Typically, computational simulations employ values from Johnson & Christy’s tabulation or Palik’s handbook which are known to contain inaccuracies and are also limited to simple material compositions. A database of experimentally-derived optical constants for more complex materials therefore has value. We present the high-throughput synthesis of plasmonic alloys and rapid characterisation of their optical properties as a function of both composition and wavelength. The variance in refractive index and extinction coefficient show correlation with lattice parameter, crystalline phases of intermetallic compounds and other quality factors that would not be taken into account with a traditional effective medium approximation (weighted averaging of n & k with composition). Moreover, ellipsometry of compositional gradient thin films which are 1) metallic, 2) optically thick, and 3) smooth and highly reflective is an effective method for rapidly assessing the optical constants of complex plasmonic alloy systems.

We present a model for the optical design of gradient-index (GRIN) media of general rotationally symmetric form, based on any number of constituent materials. This is achieved by modelling the relative composition of the medium as a function of space in a form that may be readily converted to refractive index and its derivatives, and is also suitable for optimisation in lens design software. This model is used in the optical design of a singlet GRIN eyepiece where we demonstrate equivalent performance to a multi-element homogeneous design. We show the potential of such media for correction of both chromatic and monochromatic aberrations. Whilst conventional optical systems depend on a set of homogeneous media bounded by discontinuous surfaces, such arbitrary GRIN media introduce the scope for a class of continuous optical systems where the majority of optical work is performed by GRIN media. We explore concepts for the optical design of such systems.

The applications for larger format infrared focal plane arrays are numerous: more pixels on target, wider fields of regard, and digital windowing while retaining the highest resolutions possible are just a few examples. As manufacturing capabilities at the sensor level begin rising to meet these challenges, it is imperative advancements in the design and manufacturing practices of optical assemblies run in parallel. The principle challenges met by optical designers in this field are those driven by the size of the optical elements required. This paper will detail some of these challenges, specifically the form of the lens design and the difficulties of mounting and aligning large optical elements.

Infrared vision system uses infrared lens to collect radiation and focus the object onto the detector. Information such as pixel and temperature distribution could be captured and displayed as images. Infrared optics are the “eyes” of the vision system. The need of broadband, compact, low cost are driven by increasing commercial applications such as UAV, autonomous driving and smart phone. This paper presents our latest development in infrared optics design for broadband application and optics manufacturing based on Chalcogenide glasses for potential mass production. New optics design makes a single lens to achieve dual wavelength band (MWIR and LWIR) switchable. The aspheric lens and diffractive optical element (DOE) configuration are investigated to realize the broadband and compact lens design. In LWIR regime, several detector manufacturers have demonstrated both cooled and uncooled technologies with pixel size down to 12μm. It sets new standard for size, weight, power and performance in terms of resolution. Chalcogenide material is gradually taking over Germanium in broad IR regime. It performs especially well in the 8 to 12μm range, because of its lowest absorption and dispersion in LWIR. The low dn/dT of the Chalcogenide makes lens athermalization much simpler by removing required mechanical compensation complexity. The Chalcogenide series of glasses can be processed by molding. As compare to the polished/machined glass lens which take more than 1 hour for each piece, the molding process time will be reduced to 5 mins.

With new detectors that are capable of imaging across multiple wavelength bands, new methods need to be developed to reduce the lens count and improve performance across these multiple bands while minimizing the SWAP-c (Size, Weight, power and cost) of the system. One method that was proposed was using an update to the classical γν-ν diagram. This method which, uses instantaneous Abbe number and minimum dispersion wavelength to select materials that minimize the chromatic and thermal focal shift over the desired spectral region. A MWIR/LWIR lens was designed using this method to minimize the lens count. The lens has a continuous 3x zoom range. The lens was manufactured to determine the validity of the method that was used and to evaluate the new materials that are being developed. A comparison of the nominal design to the manufactured design is discussed. This includes a comparison of MTF performance.

There is a growing need for lenses capable of determining the precise object distance and field of view (FOV) which needs to be met with a high degree of accuracy and repeatability. Difficulties achieving this accuracy arise with zoom lenses due to the dependence of field of view on the focus position. The depth of field phenomenon is also an issue which must be addressed. In addition, the accurate measurement of element positions can also be an issue. In this paper, we will explore these challenges and offer a solution in the form of metric zoom capability.

air-LUSI is a NASA sponsored project which uses optical and robotic equipment to autonomously capture radiometric measurements of the Moon from within the science pod of an ER-2 aircraft while flying at an altitude of 70,000 feet. The air-LUSI instrument was deployed for its first engineering flight campaign on August 1st and 2nd, 2018 and captured the worlds first High Altitude Lunar Spectral Irradiance (LUSI) measurements from a semi-ground based system. By implementing instrumentation into NASA's ER-2 aircraft to produce an Airborne Lunar Observatory, unprecedented LUSI measurements can be obtained that are unadulterated from the Earth's atmosphere. By compiling a comprehensive LUSI dataset for a series of lunar phases, a Lunar Calibration Model can be further refined to provide enhanced remote sensing capabilities for some instruments in NASA's Earth Observing System (EOS). This document presents information about the flight path of the ER-2 to capture High Altitude LUSI measurements, the mechanical design of the robotic telescope, the environmental operating conditions of the design, the in flight tracking performance of the system, and the first raw lunar spectrum captured at 70,000 feet.

Additive manufacturing (AM) can change the way we design opto-mechanics. One can realize complex structures with AM that are difficult or impossible to achieve with conventional fabrication techniques. In a recent project, the US Army attempted to demonstrate athermalization of an infrared lens using AM design and manufacturing techniques. The goal was to demonstrate these new techniques in a small-scale prototype lens for a missile application.

U.S. Army Combat Capabilities Development Command, Aviation and Missile Center teamed with Materials Sciences LLC (MSC) to apply a previously-reported topology-optimization technique ^[1] to develop an additively manufactured multi-material, opto-mechanical structure. The composite structure was engineered to maintain the location of the detector focal plane at the focus of a lens as it changes with temperature. MSC initially fabricated several prototype lens housings of additively manufactured titanium and cast urethane which failed at the material interfaces during temperature cycling over the intended operational range. MSC is currently conducting fabrication trials with an injection molded thermoplastic polymer to replace the cast urethane. These unfinished prototype feedstocks are being evaluated for structural integrity under temperature cycling. Initial results are promising; but additional fabrication trials are required to produce fully dense feedstocks for finish machining.

Composite structures allow tailoring of mechanics to react as designed to temperature and vibration. But it is nearly impossible to model all aspects of a composite structure. Prototyping and testing can quickly reveal limitations of materials and fabrication methods that can inform future optimization efforts. This effort documents these iterations and learned lessons, and presents evidence that this AM-composite technique is useful for designing robust opto-mechanics and that the current manufacturing method can be matured to deliver operational components.

This paper describes design features that are being implemented in a purpose-built IR camera system to support the study of the solar corona during the 2019 Chile total eclipse. This mission is challenged by the relatively low, inband flux signal conditions present during the eclipse, and the larger system’s need to identify the specific, very narrow spectral bands of interest. With the features implemented within the dewar, the required improvement in scene contrast and detector sensitivity was achieved.

We report an image processing method which is able to break the diffraction limit for single frame images. If an image is taken by diffraction limited optical system with regularly spaced pixel detector, and if the spacing of pixels of the detector is much small than the diffraction pattern, then the spatial resolution of the image can be increased beyond the diffraction limit by using a method known as nearestneighbor- pixel-deconvolution (NNPD). Initial experiment result has proved feasibility of this method. Two images captured from outer space were processed using this method, with some new features unveiled in the processed images.

In this paper is presented an IR imaging technique allowing one to retrieve quantitative concentration and temperature maps with relatively fast acquisition times of samples evolving in time. A model study is realized based on the drying of a drop of colloidal dispersion in confined geometry and quantitative maps of colloid volume fraction and temperature everywhere in the dorp are retrieved. Finally, a secondary technique of IR tomography is presented to extend the setup sensitivity to the thickness of the sample and 3D tomographs of both thermal emissivity and IR absorbance of a silica gel are constructed numerically.

The latest generation of optical sensing hardware comprise optical surfaces without rotational symmetry, commonly known as freeform optics. Whether the goal is obtaining more information by using a larger aperture and/or field of view or to decrease the overall footprint of the system, freeform optics have demonstrated unique capabilities to enable these advancements. However, it is critical to use concurrent engineering practices between design, fabrication, and testing to ensure that the final system meets the required design specifications after applying manufacturing tolerances, can be fabricated, and is able to be tested using the available technologies, all while staying within the budget for the project. Here, we describe the collaborative effort between two universities, specifically as it relates to optical design, to create a 250 mm aperture-class telescope that operates at F/3 over a full field of view of 3 degrees along the diagonal. The optical system utilizes all reflective surfaces whose surface shapes are freeforms described by orthogonal polynomials. The freeform benefit was realized in the package size of the system, which was minimized to the extent possible (40 liters) while maintaining diffraction-limited optical performance over the full field-of-view in the visible spectrum.

This manuscript is the second of three submissions to describe the concurrent engineering of a 250 mm aperture class three mirror anastigmatic (TMA) visible spectrum imager. The system is an off axis, F/3, 3 degree FOV imager with all freeform mirrors. The major drivers for the mechanical design were low mass, stiffness, robustness, thermal stability, and scalablility. The system is designed using silicon carbide (SiC) for the optics and housing to meet these requirements. The scope of this manuscript is limited to aluminum prototype optics, which are identical to the SiC components. Here, we describe the mechanical design process to light weight the optics while maintaining adequate stiffness. Also described is the pairing of the optic with an optical cell for both the manufacture and system integration using kinematic mounts. The mount design pairs with a matched kinematic mount for off machine figure metrology. This allows for an iterative figure convergence process. A design for manufacture and metrology approach was used to ensure the system elements can be both manufactured and measured by providing feedback to the optical designers.

The latest generation of optical sensing hardware comprises of optical surfaces without rotational symmetry, commonly known as freeform optics. Whether the goal is obtaining more information by using a larger aperture and/or field of view or to decrease the overall footprint of the system, freeform optics have demonstrated unique capabilities to enable these advancements. However, it is critical to use concurrent engineering practices between optical design, mechanical design, manufacture, and metrology to ensure that the final system meets the required optical design specs after applying manufacturing tolerances. Metrology of freeform optics and performance testing of the three-mirror telescope will incorporate multiple measurement technologies and methods. Measurement errors are reduced through machine error corrections using a mathematical machine model and tilt induced error correction in mid-spatial frequency measurements using a scanning white light interferometer (SWLI). The form measurement uncertainty will be evaluated using the machine model and the Monte Carlo method for simulating possible measurement results taking into consideration the uncertainty in the machine error measurements and probe measurement uncertainty. Form measurements include contact and non-contact instruments with different sampling strategies. SWLI and stylus measurements for surface roughness are utilized for both areal and profile measurements. Design for metrology" aims to inform the design and manufacturing process definition as part of the concurrent engineering goal. By considering metrology in the initial design and manufacturing through ease of mounting and appropriate fiducials it is possible to reduce wasted effort and manufacturing time.