Proceedings Volume 8016

Window and Dome Technologies and Materials XII

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Proceedings Volume 8016

Window and Dome Technologies and Materials XII

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Volume Details

Date Published: 20 May 2011
Contents: 9 Sessions, 30 Papers, 0 Presentations
Conference: SPIE Defense, Security, and Sensing 2011
Volume Number: 8016

Table of Contents

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Table of Contents

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  • Front Matter: Volume 8016
  • Advances in Mid-Wavelength Infrared Window Technology I
  • Advances in Mid-Wavelength Infrared Window Technology II
  • Optical Properties: Measurement and Prediction
  • Advances in Long-Wavelength Infrared Window Technology
  • State-of-the Art in Optical Finishing
  • Optical Surface Treatments and Microstructures
  • Metrology of Free-Form and Conformal Optics
  • Thin Film Optical Coatings and Analysis
Front Matter: Volume 8016
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Front Matter: Volume 8016
This PDF file contains the front matter associated with SPIE Proceedings Volume 8016, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.
Advances in Mid-Wavelength Infrared Window Technology I
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Effects and elimination of nanoporosity in transparent sintered spinel (MgAl[sub]2[/sub]O[sub]4[/sub])
Andreas Krell, Katja Waetzig, Jens Klimke
MgAl2O4 is a candidate for sintered windows, domes and lenses for UV, visible, and IR applications. However, exact Mie calculation shows that for imaging uses with a window thickness of e.g. 5 mm even IR transmission will not tolerate smallest amounts of 0.01% of 50-100 nm small pores, and the impact of such pores is even worse at shorter wave lengths. Principles of solid state sintering suggest that smallest pores should be eliminated more easily than larger ones. It is, however, observed that a significant population of 50-100 nm small nanopores exists in undoped transparent spinel ceramics after hot-isostatic pressing with the higher concentration the finer the particles of the raw spinel powder are. On the other hand, it is demonstrated that sintering densification is governed not only by the size of the ceramic powder particles and the homogeneity of their mutual coordination but also by the state of the crystal lattice. Taking advantage of this latter effect, sintered spinel ceramics were derived by reactive sintering of undoped MgO/Al2O3 mixtures resulting in an in-line transmittance which fits comparable spinel single crystals from 200nm wave length up to the IR range.
Manufacturing solutions for polycrystalline transparent spinel domes
Magnesium aluminate spinel is a durable, broadband, electro-optical material that can be readily manufactured into transparent domes for multimode seeker applications. Technology Assessment & Transfer, Inc. reports on the results of its Army SBIR-funded research and development efforts to resolve manufacturing issues with regard to transparent spinel domes. The specific areas of study have been cost, quality, and ability to scale up to full production. Alternative manufacturing approaches were evaluated and compared. A clear path to full scale production has been identified.
High-performance spinel ceramics for IR windows and domes
Juan L. Sepulveda, Raouf O. Loutfy, Sekyung Chang, et al.
High performance spinel ceramic is required for near-term future applications based on the excellent spinel transmission properties in the UV-VIS-Mid IR wavelength range. Windows as large as 30"x60" and hemispherical domes 4"-7" in diameter have been distinguished as applications where the novel spinel technology could be successfully applied. Future applications involve the use of even more complex 3-D shapes like spinel superdomes and tubes. The thickness of some of these components has reached 1" and above. MER has been actively pursuing these design objectives and has shown the feasibility of producing some of these complex shaped parts. Optimization of transmittance and strength are always the main objective. MER has also been pursuing edge bonding technology, where large thick panes will be edge bonded into a final large window. The production of monolithic windows as large as 18"x22", which can be used as individual windows or as panes prior to edge bonding, has also been demonstrated. Using the complex 3-D spinel process, MER has also demonstrated the feasibility of producing 4"-7" diameter hemispherical domes blanks of very high quality. After rendering and polishing, defect free domes have been produced. The process has been characterized and qualified using an optical grade spinel specification. Details of MER's technology to produce low cost, high strength, transparent magnesium aluminum spinel windows and domes are described. High optical and IR transparency in the 0.3 - 5.5 μm wavelength range is obtained. Equibiaxial strength averages 180-200 MPa, with individual readings reaching 300-320 MPa maximum. Spinel optical and mechanical properties are provided.
Advances in Mid-Wavelength Infrared Window Technology II
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ALON optical ceramic transparencies for window, dome, and transparent armor applications
Surmet continues to invest in and expand its manufacturing capability for ALON® Optical Ceramic, as the market demand for this material increases. The biggest demand and opportunity continues to be in the area of transparent armor, however, the market for sensor domes and windows, made from ALON, continues to grow at an impressive rate as well. ALON® Transparent Armor's unsurpassed ballistic performance, combined with the robustness of ALON's manufacturing process and reproducibly high material quality make ALON the leading candidate for many future armor systems. Recent results for ALON armor windows will be presented. Advances being made in Surmet's production capability to support the very large quantities of material required by the transparent armor market also benefit the sensor market. Improvements in quality, quantity and manufacturability of ALON material, combined with improvements being made in optical quality, ensure a robust supply of high quality material for high volume window and dome applications. Recent advancement in ALON® window and dome blanks, as well as in optical fabrication will be presented.
High-impact resistance optical sensor windows
Joel Askinazi, Mark L. Ceccorulli, Lee Goldman
Recent field experience with optical sensor windows on both ground and airborne platforms has shown a significant increase in window fracturing from foreign object debris (FOD) impacts and as a by-product of asymmetrical warfare. Common optical sensor window materials such as borosilicate glass do not typically have high impact resistance. Emerging advanced optical window materials such as aluminum oxynitride offer the potential for a significant improvement in FOD impact resistance due to their superior surface hardness, fracture toughness and strength properties. To confirm the potential impact resistance improvement achievable with these emerging materials, Goodrich ISR Systems in collaboration with Surmet Corporation undertook a set of comparative FOD impact tests of optical sensor windows made from borosilicate glass and from aluminum oxynitride. It was demonstrated that the aluminum oxynitride windows could withstand up to three times the FOD impact velocity (as compared with borosilicate glass) before fracture would occur. These highly encouraging test results confirm the utility of this new highly viable window solution for use on new ground and airborne window multispectral applications as well as a retrofit to current production windows. We believe that this solution can go a long way to significantly reducing the frequency and life cycle cost of window replacement.
Dual IR/RF windows for laser communications
Lee M. Goldman, Richard Twedt, Jayson Zigman, et al.
Future advanced communications systems will utilize lasers which operate at 1.55μm backed up by an RF links. To the extent that such systems utilize a common aperture, dual IR/RF windows and domes will be required. The durability of such windows, with respect to rain and sand erosion damage, is an important consideration as damaged surfaces will lead to significant optical degradation for operation at 1.55μm. This requirement drives the materials choices toward more durable materials such as ALON® optical ceramic, spinel and sapphire. Single layer windows, with appropriately selected thicknesses of these materials can be used for narrow RF wavebands, but are not adequate for applications requiring broadband RF transparency. To this end, multilayer windows, with durable outer layers of ALON have been developed, and built. Recent results will be presented.
Transparent ceramics for demanding optical applications
Mark Parish, Marina Pascucci, Normand Corbin, et al.
Transparent ceramics are finding applications is demanding optical applications were traditional mineral salts and amorphous materials are limited and single crystals are not practical. Polycrystalline ceramics offer a unique combination of mechanical, electrical and optical properties that allow window and dome applications and possibilities that were previously not possible. Transparent ceramics are being developed for use in a number of applications with each material possessing a distinctive set of properties that address a particular application. The current status of CeraNova's fine grain transparent ceramic programs for dome and window applications will be presented with emphasis on their exceptional properties for specific applications.
Colloidal processing and optical transmittance of submicron polycrystalline alumina
Tzu-Chien Wen, Dinesh K. Shetty
Grain-boundary scattering due to intrinsic birefringence limits the optical transmittance of polycrystalline alumina (PCA). Smallest grain size and highest density are desired for maximum real in-line transmittance (RIT). Grain size versus density or sintering path plots were employed to compare different colloidal routes for fabricating green bodies followed by pressureless sintering and hot-isostatic pressing. Compacts fabricated by colloidal pressing showed superior density at similar grain size as compared to slip-cast compacts. The real in-line transmittance of the PCA was measured over a range of wavelengths (0.19-10 μm). The compacts fabricated by colloidal pressing showed higher transmittance as compared to slip-cast specimens. The measured transmittance was still, however, slightly lower than the theoretical values predicted by the grain-boundary scattering model of Apetz and van Bruggen. The grain-size dependence of RIT was analyzed using a model that combined grain-boundary scattering and scattering by isolated grain-boundary pores.
Synthesis, characterization, and densification of Al[sub]2-x[/sub]Sc[sub]x[/sub](WO[sub]4[/sub])[sub]3[/sub] ceramics for low-expansion infrared-transparent windows
Niladri Dasgupta, Bruce Butler, Erinn Sörge, et al.
Materials and Systems Research, Inc. is developing a material with a low coefficient of thermal expansion (CTE) that could be used in an infrared-transparent window. The material is derived from a solid solution of Al2(WO4)3, which has positive thermal expansion, and Sc2(WO4)3 with a negative thermal expansion. An optimum composition of Al 0.5 Sc1.5(WO4)3 was identified by synthesizing solid solutions, Al2-xScx(WO4)3, by a solid-state route with compositions ranging from x = 0 to 2.0. A single orthorhombic phase was obtained at all compositions. A composition corresponding to x = 1.5 had a low CTE value of -0.15 x 10-6/oC in the temperature range, 25-700ºC. A low temperature solution combustion process was developed for this optimum composition resulting in a single phase powder with a surface area of ~ 14 m2/g and average particle size (as determined from surface area) of 91 nm. Preliminary densification experiments via dry uniaxial pressing and pressureless sintering at 1100°C for 2 hours resulted in a sintered compact 97.5% in density and submicron grain size.
Optical Properties: Measurement and Prediction
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A mid-infrared prism coupler for bulk and thin film optical analysis
Norman C. Anheier, Hong A. Qiao
In this paper we present a prism coupler that is capable of characterizing optical dispersion and thermal index variations (dn/dT) in bulk and thin film materials at measurement wavelengths extending through the mid-infrared (3 to 12 μm). Our research was motivated by the need for precise, rapid, and low cost optical refractive index analysis to facilitate development of new mid-infrared optical materials, assessment of variability in mid-infrared optical materials acquired from commercial sources, and design of optical elements used in advanced, high performance mid-infrared sensing platforms. Such efforts commonly require ±1x10-3 or better absolute index measurement accuracy at measurement wavelengths spanning from the visible to the mid-infrared. Unfortunately most dispersion and dn/dT characterization methods require compromises in accuracy, cost, and timeliness, or cannot access the mid-infrared spectral region where many of the most important sensing and defense applications exist. A prism coupler, implemented at the mid-infrared, was found to provide rapid and cost-effective optical materials metrology with sufficient accuracy to meet most design requirements. We discuss the challenges of integrating the required mid-infrared optical components, including a sensitive mid-infrared detector and the quantum cascade and other infrared laser sources, with a commercial Metricon prism coupler and the calibration steps necessary to achieve the desired measurement accuracy.
Measurement of chalcogenide glass optical dispersion using a mid-infrared prism coupler
Hong A. Qiao, Norm C. Anheier, J. David Musgrave, et al.
Physical properties of chalcogenide glass, including broadband infrared transparency, high refractive index, low glass transition temperature, and nonlinear properties, make them attractive candidates for advanced mid-infrared (3 to 12 μm) optical designs. Efforts focused at developing new chalcogenide glass formulations and processing methods require rapid quantitative evaluation of their optical constants to guide the materials research. However, characterization of important optical parameters such as optical dispersion and thermal coefficient remains a slow and costly process, generally with limited accuracy. The recent development of a prism coupler at the Pacific Northwest National Laboratory (PNNL) now enables rapid, high precision measurement of refractive indices at discrete wavelengths from the visible to the mid-infrared. Optical dispersion data of several chalcogenide glass families were collected using this method. Variations in the optical dispersion were correlated to glass composition and compared against measurements using other methods. While this work has been focused on facilitating chalcogenide glass synthesis, mid-infrared prism coupler analysis has broader applications to other mid-infrared optical material development efforts, including oxide glasses and crystalline materials.
Methods for prediction of refractive index in glasses for the infrared
It is often useful to obtain custom glasses that meet particular requirements of refractive index and dispersion for highend optical design and applications. In the case of infrared glasses, limited experimental data are available due to difficulties in processing of these glasses and also measuring refractive indices accurately. This paper proposes methods to estimate refractive index and dispersion as a function of composition for selected infrared-transmitting glasses. Methods for refractive index determination are reviewed and evaluated, including Gladstone-Dale, Wemple- DiDomenico single oscillator, Optical basicity, and Lorentz-Lorenz total polarizability. Various estimates for a set of PbO-Bi2O3-Ga2O3 (heavy metal oxide) and As-S (chalcogenide) glasses will be compared with measured values of index and dispersion.
Multiphonon difference band absorption in diamond
The longwave absorption coefficient of diamond is composed of the two-phonon red wing and multiphonon difference (hot) bands. As temperature increases the difference bands rapidly grow in strength and dominate the absorption. A variation on a multiphonon sum band model is developed for difference bands and applied to a temperature dependent data set on CVD polycrystalline diamond that are 1.54 mm thick. The model can also be used to estimate multiphonon difference band contribution to the refractive index.
Advances in Long-Wavelength Infrared Window Technology
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Anisotropy in structural and optical properties of chemical vapor deposited ZnS
Significant anisotropy in as-deposited CVD ZnS at several length scales has been demonstrated through investigation of structural and optical properties. Compressive strength of cylinders of CVD ZnS oriented in the growth direction is ~50% higher than cylinders taken perpendicular to the growth direction. Lattice parameter measurements of mandrel side (first-to-grow) material is ~0.4% smaller than growth side (last-to-grow) material in a cored sample representing ~500 hours of CVD growth, indicating significant strain along the growth direction. X-ray diffraction also shows evidence of preferred orientations for hexagonality which differ depending on position in the growth history. In crosssection, the cored sample shows several large bands which are correlated with different degrees of infrared absorption and BTDF scattering. However, no universal trend is found that applies to the whole length from the mandrel to the growth side regarding optical properties. The extinction in the visible and infrared is lower for measurements perpendicular to the growth axis than parallel to it, possibly due to scattering from the growth bands.
Bimodal Weibull statistical analysis of CVD-ZnSe and CVD-ZnS flexural strength data
The results of flexural strength The results of flexural strength testing performed on brittle materials are usually interpreted in the light of a "Weibull plot," i.e., by fitting the estimated cumulative failure probability (CFP) to a linearized semiempirical Weibull distribution. This procedure ignores the impact of the testing method on the measures stressed at failure-specifically the stressed area and the stress profile-thus resulting in an inadequate characterization of the material under consideration. In a previous publication [Opt. Eng. 41, 3151 (2002)] the author reformulated Weibull's statistical theory of fracture in a manner that emphasizes how the stressed area and the stress profile control the CFP, a 1-sq.cm uniformly stressed area. Fitting the CFP of IR-transmitting materials was performed by means of nonlinear regressions but produced evidence of systematic deviations. In this paper we demonstrate that, upon extending the previously elaborated model to distributions involving two distinct types of defects (bimodal distributions), fitting the estimated CFP of CVD-ZnS or CVD-ZnSe leads to a much improved description of the fracture process. In particular, the availability of two sets of statistical parameters (characteristic strength and shape parameter) can be taken advantage of for evaluating the failure-probability density, thus providing means of assessing the nature, the critical size, and the size distribution of the surface/subsurface flaws.
Microwave mediated synthesis of ZnS spherical nanoparticles for IR optical ceramics
D. Ravichandran, T. Wharton, B. Devan, et al.
The existing material choice for long-wave infrared (LWIR) and semi-active laser domes is multispectral zinc sulfide (ZnS), made by chemical vapor deposition. An alternative route to make more erosion-resistant ZnS could be through hot pressing ZnS nanoparticles into small-grain material. We have attempted to produce ZnS nanoparticles both by microwave and microwave-hydrothermal methods. Microwave route produced ultrahigh purity, homogeneous, well dispersed, and uniformly spherical ZnS nanoparticles. Microwave-hydrothermal route produced equiaxed cubic-faceted nanoparticles. The powder X-ray diffraction patterns of ZnS shows the presence of broad reflections corresponding to the (1 1 1), (2 2 0), and (3 1 1) planes of the cubic crystalline ZnS material. The domain size of the particles estimated from the Debye-Scherrer formula for the main reflection (111) gives a value of 2.9 and 2.5 for the microwave and microwave-hydrothermal methods respectively.
Single crystal and polycrystalline CVD diamond for demanding optical applications
J. M. Dodson, J. R. Brandon, H. K. Dhillon, et al.
Diamond's extremely wide transparency, combined with its other exceptional properties including hardness, strength and thermal conductivity make it a desirable material for optical windows. Polycrystalline diamond grown by chemical vapour deposition (CVD) has become the preferred window material for high power CO2 laser systems since its development in the 1990s. The range and availability of diamond materials is expanding, and in recent years has been extended to include CVD single crystal diamond. This paper reviews the quality of these materials, looking at optical scatter and absorption around 1 and 10 microns, along with their thermal and mechanical properties. We also discuss selection of appropriate grades and how they may best be integrated into demanding optical applications.
State-of-the Art in Optical Finishing
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History of magnetorheological finishing
Magnetorheological finishing (MRF) is a deterministic method for producing complex optics with figure accuracy <50 nm and surface roughness <1 nm. MRF was invented at the Luikov Institute of Heat and Mass Transfer in Minsk, Belarus in the late 1980s by a team led by William Kordonski. When the Soviet Union opened up, New York businessman Lowell Mintz was invited to Minsk in 1990 to explore possibilities for technology transfer. Mintz was told of the potential for MRF, but did not understand whether it had value. Mintz was referred to Harvey Pollicove at the Center for Optics Manufacturing of the University of Rochester. As a result of their conversation, they sent Prof. Steve Jacobs to visit Minsk and evaluate MRF. From Jacobs' positive findings, and with support from Lowell Mintz, Kordonski and his colleagues were invited in 1993 to work at the Center for Optics Manufacturing with Jacobs and Don Golini to refine MRF technology. A "preprototype" finishing machine was operating by 1994. Prof. Greg Forbes and doctoral student Paul Dumas developed algorithms for deterministic control of MRF. In 1996, Golini recognized the commercial potential of MRF, secured investment capital from Lowell Mintz, and founded QED Technologies. The first commercial MRF machine was unveiled in 1998. It was followed by more advanced models and by groundbreaking subaperture stitching interferometers for metrology. In 2006, QED was acquired by and became a division of Cabot Microelectronics. This paper recounts the history of the development of MRF and the founding of QED Technologies.
Rapid optical manufacturing of hard ceramic conformal windows and domes
J. DeGroote Nelson, A. Gould, D. Dworzanski, et al.
Hard ceramic conformal windows and domes provide challenges to the optical fabricator. The material hardness, polycrystalline nature and non-traditional shape demand creative optical fabrication techniques to produce these types of optics cost-effectively. VIBETM is a high-speed, high-pressure, conformal optical fabrication process that is capable of rapidly polishing hard ceramic materials and non-traditional shapes such as toroids and tangent ogives. This paper will overview the recent progress made to rapidly manufacture hard ceramic conformal windows and domes as well as the challenges associated with it. Results will show 10-50x increase in removal rates using the VIBE platform to polish hard ceramic materials compared to conventional methods.
Ogive and free-form polishing with ultraform finishing
UltraForm Finishing (UFF), OptiPro Systems' five axis sub-aperture polishing machine has evolved from an initial prototype into a robust aspheric manufacturing system that can rapidly produce finished aspheres directly from a ground surface. UFF utilizes a belt of polishing material 50" long supported by a polyurethane wheel to polish a wide variety of materials ranging from traditional glasses to IR materials. This belt polishing system provides a tuned stiffness that is capable of conforming to the polishing surface without replicating the surface roughness. When combined with state of the art figure correction algorithms, the UFF is capable of robust and deterministic figure correction for aspheric surfaces. Recently, OptiPro Systems has expanded the capability of the UFF to include deep concave ogive and free-form surfaces. Although these types of surfaces can be beneficial from an optical or aerodynamic standpoint they pose additional challenges both from their steep geometry as well as from a polishing tool path perspective. A brief description of these challenges as well as possible solutions to these problems will be presented. In addition, the current figure correction capability of the system utilizing feedback from OptiPro's five axis non-contact free-form metrology system will be presented.
Optical Surface Treatments and Microstructures
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Moldable AR microstructures for improved laser transmission and damage resistance in CIRCM fiber optic beam delivery systems
Bruce D. MacLeod, Douglas S. Hobbs, Ernest Sabatino III
Anti-reflecting (AR) surface relief microstructures (ARMs) are being developed as a replacement for thin-film AR coatings in laser-based systems to improve light transmission, power handling, operational bandwidth, and system reliability. Because ARMs textures have the potential to be replicated using simple embossing methods, the performance advantage and robustness of ARMs can be extended to moldable mid-infrared transmitting materials such as chalcogenide optical fibers. In this work, the optical performance of mid-infrared transparencies incorporating ARMs textures replicated from a master template has been modeled, and multiple master stamping tools have been fabricated in materials such as diamond, silicon carbide, nickel, silicon, and sapphire. Images from ARMs texture embossing trials using arsenic sulfide and arsenic selenide (AMTIR2) glasses, and fluoride glasses such as ZBLAN and indium fluoride provided by IRPhotonics, show excellent pattern transfer and fidelity. Transmission measurements of ARMs textures stamped into arsenic sulfide and arsenic selenide windows show broadband infrared performance equivalent to ARMs textured windows processed by direct patterning and etch methods. A system for molding ARMs textures directly into the end facets of multi-mode mid-infrared transmitting fibers is yielding promising initial results.
Development of nanostructured protective "sight glasses" for IR gas sensors
René Bergmann, Zachary James Davis, Michael Stenbæk Schmidt, et al.
In this work protective "sight glasses" for infrared gas sensors showing a sub-wavelength nanostructure with random patterns have been fabricated by reactive ion etching (RIE) in an easy and comparable cheap single step mask-less process. By an organic coating, the intrinsic water repellent property of the surface could be enhanced, shown by contact angle and roll-off angle measurements. The "self-cleaning" surface property and chemical robustness towards aggressive environments are demonstrated. FT-IR spectroscopy concerning the optical properties of these nanostructured silicon windows revealed a stable anti-reflective "moth-eye" effect in certain wavelength ranges owing to the nanostructures.
Laser damage resistant anti-reflection microstructures in Raytheon ceramic YAG, sapphire, ALON, and quartz
Douglas S. Hobbs, Bruce D. MacLeod, Ernest Sabatino III, et al.
A study of the laser induced damage threshold (LiDT) of anti-reflection (AR) microstructures (ARMs) built in the end facets of metal ion doped yttrium aluminum garnet (YAG) laser gain material, has been conducted. Test samples of undoped and ytterbium-doped polycrystalline YAG produced by Raytheon Company were processed with ARMs in one surface and subjected to standardized pulsed LiDT testing at the near-infrared (NIR) wavelength of 1064nm. As received YAG samples with a simple commercial polish were also submitted to the damage tests for comparison, along with YAG samples that were treated with a single layer thin-film AR coating designed for maximum transmission at 1064nm. Additional samples of single crystal sapphire and quartz, and polycrystalline ALONTM windows were prepared with thin-film AR coatings and ARMs textures to expand the 1064nm laser damage testing to other important NIR transmitting materials. It was found that the pulsed laser damage resistance of ARMs textured ceramic YAG windows is 11 J/cm2, a value that is 43% higher than untreated ceramic YAG windows, suggesting that ARMs fabrication removed residual sub-surface damage, a factor that has been shown to be important for increasing the damage resistance of an optic. This conclusion is also supported by the high damage threshold values found with the single layer AR coatings on ceramic YAG where the coatings may have shielded the sub-surface polishing damage. Testing results for the highly polished sapphire windows also support the notion that better surface preparation produces higher damage resistance. The damage threshold for untreated sapphire windows exceeded 32 J/cm2 for one sample with an average of 27.5 J/cm2 for the two samples tested. The ARMs-treated sapphire windows had similar damage thresholds as the untreated material, averaging 24.9 J/cm2, a value 1.5 to 2 times higher than the damage threshold of the thin film AR coated sapphire windows.
Numerical comparison of grid pattern diffraction effects through measurement and modeling with OptiScan software
Coatings of various metalized patterns are used for heating and electromagnetic interference (EMI) shielding applications. Previous work has focused on macro differences between different types of grids, and has shown good correlation between measurements and analyses of grid diffraction. To advance this work, we have utilized the University of Arizona's OptiScan software, which has been optimized for this application by using the Babinet Principle. When operating on an appropriate computer system, this algorithm produces results hundreds of times faster than standard Fourier-based methods, and allows realistic cases to be modeled for the first time. By using previously published derivations by Exotic Electro-Optics, we compare diffraction performance of repeating and randomized grid patterns with equivalent sheet resistance using numerical performance metrics. Grid patterns of each type are printed on optical substrates and measured energy is compared against modeled energy.
Metrology of Free-Form and Conformal Optics
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Advances in freeform optical metrology using a multibeam low-coherence optical probe (Quad-Probe)
Conformal windows reduce drag, but introduce optical aberrations. Corrector optics minimize such optical aberrations, but they feature complex surfaces that cannot presently be measured interferometrically. To address this problem, ASE Optics has developed a non-contact "Quad-Probe" that measure the position and orientation of surfaces. By scanning the probe over the surface of the optic, a 3D model of the interior and exterior surfaces can be built. Furthermore, the Quad-Probe can be used inside a polishing machine, and feedback from the Quad-Probe can be used to guide the scanner in measuring an unknown part.
A non-contact surface measurement system for freeform and conformal optics
OptiPro Systems has been developing the UltraSurf, a non-contact measuring system using state of the art, precision motion control. The goal is to precisely scan standard optical shapes such as concave and convex spherical surfaces, as well as the complex geometries of aspheric, ogive, and freeform shapes without the limitations associated with other measurement methods. Common optical measurement methods have limitations with surface roughness, slope error, and deviation from best-fit sphere. Optipro designed the UltraSurf to further the manufacturing capabilities of companies generating complex precision optics. The UltraSurf measures with sub-micrometer non-contact point sensors to collect surface information. Various sensors are commercially available from multiple companies, each with their own distinct optical measuring technology. One optical sensor uses white light confocal chromatic imaging to measure individual optical surfaces. Another optical sensor uses low-coherence interferometry with a near infrared laser, and is able to measure the inside, outside, and thickness of optical materials at a single point. The UltraSurf scans the optical sensors over the surface of the part under test, keeping it normal to the surface. The single point measuring method coupled with computer-controlled motion gives the UltraSurf flexibility to measure greatly varied geometries. Ultimately, a point cloud of the measured surface is generated. The cloud can be used to calculate deviation from the desired shape, as well as various surface parameters. Applications, definitions, and measurement results of freeform and conformal shapes using UltraSurf will be presented.
Interferometric tomography: a new tool for metrology on conformal optics
Mikhail Gutin, Olga Gutin, Xu-Ming Wang, et al.
Fabrication and measurement of conformal aerodynamic windows and domes to precise optical tolerances from ceramic materials remains a problem. This paper describes the development of the Interferometric Tomography inspection system, based on a new method for wavefront and surface metrology on optics with very high aberrations. The metrology system is a modular attachment for integrating a standard commercial interferometer with an existing optical fabrication tool. The system will enable high precision measurement of infrared windows and domes in the process of their fabrication, until finished to specification. The capability for fabrication and metrology of aggressively aspheric optics, "aberrated by design", will enable new optical designs of higher performance and lower cost, compared to existing optics.
Thin Film Optical Coatings and Analysis
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Low-loss dual-wave laser optics coatings at 1060 nm and 530 nm
Red-to-green laser conversion requires dual-wave laser optics coatings at 1060nm and 530nm. Loss analysis of the dual-wave coatings were presented for 3 types of coating designs with a coating material combination of HfO2/SiO2. Homogeneity and smoothness of the HfO2/SiO2 multilayers via standard plasma ion assisted deposition were evaluated. A modified plasma ion assisted deposition process with in-situ plasma smoothing was developed to deposit dense and smooth HfO2/SiO2 multilayers. Improved film microstructure was revealed on single layer and multilayer coated samples by means of atomic force microscopy and scanning electron microscopy. The improved film microstructure led to low loss and laser durable coating performance.
Flexible transparent electrode
Hulya Demiryont, Kenneth C. Shannon III, David Moorehead, et al.
This paper presents the properties of the EclipseTECTM transparent conductor. EclipseTECTM is a room temperature deposited nanostructured thin film coating system comprised of metal-oxide semiconductor elements. The system possesses metal-like conductivity and glass-like transparency in the visible region. These highly conductive TEC films exhibit high shielding efficiency (35dB at 1 to 100GHz). EclipseTECTM can be deposited on rigid or flexible substrates. For example, EclipseTECTM deposited on polyethylene terephthalate (PET) is extremely flexible that can be rolled around a 9mm diameter cylinder with little or no reduction in electrical conductivity and that can assume pre-extension states after an applied stress is relieved. The TEC is colorless and has been tailored to have high visible transmittance which matches the eye sensitivity curve and allows the viewing of true background colors through the coating. EclipseTECTM is flexible, durable and can be tailored at the interface for applications such as electron- or hole-injecting OLED electrodes as well as electrodes in flexible displays. Tunable work function and optical design flexibility also make EclipseTECTM well-suited as a candidate for grid electrode replacement in next-generation photovoltaic cells.