Proceedings Volume 6666

Optical Materials and Structures Technologies III

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Proceedings Volume 6666

Optical Materials and Structures Technologies III

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Volume Details

Date Published: 13 September 2007
Contents: 11 Sessions, 34 Papers, 0 Presentations
Conference: Optical Engineering + Applications 2007
Volume Number: 6666

Table of Contents

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Table of Contents

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  • Front Matter: Volume 6666
  • Glass and Glass-Ceramics
  • SiC Processing and Characterization I
  • SiC Processing and Characterization II
  • Silicon + Carbon = Silicon Carbide I
  • Silicon + Carbon = Silicon Carbide II
  • Silicon + Carbon = Silicon Carbide III
  • Beryllium and Metals I
  • Beryllium and Metals II
  • MASTER's Session
  • Poster Session
Front Matter: Volume 6666
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Front Matter: Volume 6666
This PDF file contains the front matter associated with SPIE Proceedings Volume 6666, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Glass and Glass-Ceramics
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Manufacturing of lightweighted ZERODUR components at SCHOTT
Thorsten Döhring, Armin Thomas, Ralf Jedamzik, et al.
There is a broad range of applications for lightweighted components made from ZERODUR(R) glass ceramic. The main markets are secondary and tertiary mirrors for astronomical telescopes, mirrors and structural components for satellites, and mechanical structures for industrial applications, mainly in microlithography. Prominent examples from astronomy are VLT-M3, GEMINI-M2, SOFIA-M1, MAGELLAN-M2, MMT-M2, and METEOSAT-SEVIRI. At SCHOTT components with blind or undercut semiclosed holes are manufactured, typically with circular, hexagonal, rectangular or triangular shapes. The classical grinding process results in weight reduction factors of about 70 %. By additional acid etching technologies even higher lightweighting factors and rib thicknesses below 1 mm have been achieved.
Strength aspects for the design of ZERODUR glass ceramics structures
Peter Hartmann, Kurt Nattermann, Thorsten Döhring, et al.
In some applications mirrors and support structures from the zero expansion glass ceramic material ZERODUR(R) have to endure mechanical loads, e.g. rocket launches or controlled deformations for optical image correction. Like for other glassy materials the strength of glass ceramics is dominated by its surface condition. Similar to other glass ceramics ZERODUR(R) has higher strengths than glasses for comparable surface conditions. For the design of ZERODUR(R) parts well known rules of thumb for its strength are not sufficient in any case. So new information and data with enlarged sample sets and hence better statistics have been collected to improve the understanding of its behavior under mechanical loads. Finally an outlook is given on the application of ZERODUR(R) in ambitious current and future space projects.
Athermal glass by design
This paper discusses athermal glass designed by Schafer using our proprietary GlassDESIGNTM (SGD) code. The glass formulations are dictated by choice of suitable material and application merit functions. The glass designs are subsequently manufactured for Schafer by SCHOTT North America. As an example we have designed and produced more than one-half dozen glasses with near-zero optical path difference in the visible and near-infrared portion of the spectrum. Such glasses have application for gratings, fibers, lenses and windows.
Optimization of Spectralon through numerical modeling and improved processes and designs
Bob Y. Chang, Ronald M. Huppe, Christina Chase, et al.
The demand for progressively more powerful lasers has caused those employing side-pumped laser designs to become acutely aware of pumping efficiency and performance. Additionally, precision applications demand beam stability and uniformity for the lifetime of the laser flash lamp. The use of highly diffuse, high reflectance pump chamber reflectors such as Spectralon(R)‡ have been shown to amplify overall power and performance. Spectralon is used in a wide range of side-pumped applications for its superior optical characteristics and design flexibility but stated damage thresholds of approximately 4 J/cm2 have limited it to lower power applications. To increase energy tolerances, initial damage thresholds are defined through mathematical simulation. A general form of the heat equation is studied numerically to develop a theoretical model of Spectralon's damage threshold. The heat equation is discretized using the Euler method. Secondly, process modifications are performed to test for increased material durability and to physically reproduce initially defined theoretical parameters.
SiC Processing and Characterization I
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Advances in fabrication technologies for light weight CVC SiC mirrors
Chemical Vapor Composite (CVC) Silicon Carbide (SiC) material has demonstrated superior optical polishing properties and high specific stiffness characteristics. These unique characteristics make CVC SiC a highly desirable material for aerospace reflective optics applications. The lack of material fabrication processes for CVC SiC has hindered the introduction of this material into the aerospace marketplace. Traditional methods of fabrication such as diamond grinding and lapping have proven to be expensive for CVC SiC material in aperture diameters that approximate 25cm or larger. Because of the extreme hardness of CVC SiC, the material removal rates are low and therefore larger size parts become very time consuming and thus cost prohibitive. Over the past two years several development efforts have been focused specifically toward fabrication technologies and methods to enhance the economical producibility of CVC SiC material. The results of these development efforts have revealed viable economical fabrication processes for CVC SiC. These fabrication processes have demonstrated material removal rates that are vastly greater than that of traditional diamond grinding and lapping process. This paper describes fabrications technologies and processes and material removal rates for fabricating monolithic, ultra pure, optical grade CVC SiC material.
Development of lightweight SiC mirrors for the space infrared telescope for cosmology and astrophysics (SPICA) mission
SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a Japanese astronomical infrared satellite project with a 3.5-m telescope. The target year for launch is 2017. The telescope is cooled down to 4.5 K in space by a combination of newly-developed mechanical coolers with an efficient radiative cooling system at the L2 point. The SPICA telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 μm at 4.5 K. Material for the SPICA telescope mirrors is silicon carbide (SiC). Among various types of SiC, primary candidates comprise normally-sintered SiC, reaction-sintered SiC, and carbon-fiber-reinforced SiC; the latter two have been being developed in Japan. This paper reports the current design and status of the SPICA telescope along with our recent activities on the cryogenic optical testing of SiC and C/SiC composite mirrors, including the development of an innovative support mechanism for cryogenic mirrors, which are based on lessons learned from a SiC 70 cm telescope onboard the previous Japanese infrared astronomical mission AKARI.
Development of a systematic approach to space qualification of silicon carbide for mirror applications
Iwona A. Palusinski, Isaac Ghozeil, Michael J. O'Brien, et al.
Over the last few years significant progress has been made in the development of silicon carbide (SiC) for mirror applications. These improvements include lightweighting techniques, higher production yields, and larger diameter apertures. It is now necessary to evaluate and address the systems engineering challenges facing this material to ensure space qualification and integration into future space applications. This paper highlights systems engineering challenges, suggests areas of future development, and proposes a systematic path forward that will outline necessary steps to space qualify this new material.
Metrology guided laser micromachining of SiC for mirrors
R. L. Jacobsen, M. B. Scott, J. Pitz, et al.
Silicon carbide mirrors are sought for a variety of aerospace applications. While optical polishing techniques are straight forward for flat and spherical surfaces, material removal rates for this hard, brittle material are too low for affordable processing of conventionally machined, ground, or as-produced surfaces. The problem is more severe for aspheres. This paper reports on the use of picosecond pulsed laser ablation, combined with iterative metrology, to shape the SiC in a manner that will reduce cost and lead time for mirror fabrication. The goal is to exploit relatively gentle, non-thermal ablation to produce arbitrary surface shapes in SiC that are damage free and that minimize subsequent polishing time. To apply the technology, detailed data must be developed to characterize laser-material interaction, the threshold for ablation, and the dependence of the effective "tool shape" on laser operating parameters and firing patterns. An algorithm can then be developed to calculate optimum laser guidance and firing commands for removal of the required amount of material from the ceramic surface, with reference to metrology data previously collected on the mirror blank. Recent results of machining quality, material removal rates, residual surface roughness, and suitability of surface for subsequent polishing are reported for various types of SiC and paradigms of laser micromachining.
Rapid fabrication of lightweight SiC aspheres using reactive atom plasma (RAP) processing
Polishing has traditionally been a process of mechanical abrasion with each iteration removing the damage from the previous iteration. Modern sub-aperture techniques such as CCOS, MRF polishing etc. have added a considerable amount of determinism to this iterative approach. However, such approaches suffer from one significant flaw, i.e., the algorithms are completely guided by figure error. This approach fails when there is a considerable amount of strain energy stored in the substrate and becomes very evident when the aspect ratio of the mirror increases significantly causing relaxation of strain energy to have deleterious and unpredictable effects on figure between iterations. This is particularly pronounced when the substrate is made of a hard ceramic such as silicon carbide requiring a considerable amount of pressure to obtain any appreciable material removal rate. This paper presents an alternate approach involving a stress-free figuring step and a buffing step intended to recover the surface roughness.
SiC Processing and Characterization II
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Characterization of hydrogenated silicon carbide produced by plasma enhanced chemical vapor deposition at low temperature
A new technology has been developed to grow layers of amorphous hydrogenated Silicon Carbide in vacuum, at temperatures below 100-120°C by Physical Enhanced Chemical Vapour Deposition (PE-CVD) technology. The layers have been used either to improve the surface quality of SiC mirror substrates (produced by methods different of the CVD approach, like e.g. sintered SiC) as a super-polishable cladding coatings, or to form self-sustaining thin mirrors in SiC. It should be noted that the PE-CVD claddings can be applied also to substrates different than SiC, as e.g. metals like Al or Kanigen, in order to create a high durability polishable external layer. It this paper we present the results of a wide characterization of the new material, considering the mechanical, structural and optical properties that are the most indicative parameters for its application in optics, with particular reference to the production of mirrors for ground and space astronomical applications.
Ultrasonic NDE of silicon carbide lightweight systems
Andrew R Portune, Richard A. Haber, Raymond E. Brennan
Silicon carbide (SiC) high energy mirrors from M-Cubed, Schafer Corp, Poco and Trex Inc. were investigated using nondestructive ultrasound C-scan imaging. Reflected signal amplitude variations from the top surface of the SiC mirrors were imaged to locate surface and subsurface inhomogeneities. Where possible, the bottom surface reflected signal amplitude and material velocity were mapped to evaluate bulk properties. Elastic property mapping was also performed on a dense SiC mirror sample to look for regional variations in Poisson's ratio, Young's modulus, shear modulus, and bulk modulus. These ultrasound techniques were successfully utilized for detection of subsurface inhomogeneities in the SiC mirror samples.
Silicon + Carbon = Silicon Carbide I
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SiC-SiC composites optics for UV applications
Witold Kowbel, J. C. Withers
SiC optics have been considered for numerous optical applications for a long time. The fundamental limitation of monolithic SiC is its, very low fracture toughness which greatly limits its reliability. Long fiber, SiC-SiC composites are an excellent candidate for high end optical application. The selection of the fiber and composite processing needs to address the intrinsic issues of modulus, strength, toughness, thermal conductivity and CTE isotropy. The adaptability and flexibility of SiC-SiC composite manufacturing renders the ability to fabricate very complex, closed-back structures. The fundamental issues associated with uv optics is the ability to polish the substrate to ultra high quality in order to greatly reduce the scattering.
HB-Cesic composite for space optics and structures
One of the key technologies for next generation space telescopes requiring large-scale reflectors are light-weight materials having high specific strength, high specific stiffness, low coefficient of thermal expansion and high coefficient of thermal conductivity. Several candidates, such as fused silica, beryllium, silicon carbide and carbon fiber reinforced composites, have been evaluated. An example of the latter material is a Hybrid Carbon-Fiber Reinforced SiC composite or HB-Cesic - a trademark of ECM - which has been developed by ECM and MELCO to meet the stringent space telescope requirements. Mechanical performance, such as stiffness, bending strength and fracture toughness, were significantly improved using HB-Cesic compared to our classic Cesic material. Thermal expansion and thermal conductivity of HB-Cesic at cryogenic temperatures are now partly established and excellent performance for large future space mirrors and structures are expected. In this paper we will report on the current status of development of HB-Cesic and describe the first successful applications made with this new improved material.
Design and fabrication of a single crystal silicon (SCSi) telescope: a success story
Silicon components such as mirrors and infrared lenses have been manufactured for many years, primarily from polycrystalline silicon (poly). There are inherent advantages that Single Crystal Silicon, (SCSi), has over poly, such as strength and dimensional stability, that make it more suitable for telescopes. However, there are challenges in the design of an all-SCSi telescope. SCSi is brittle and has low tensile strength compared to its compressive strength. These properties therefore dictate designs that minimize tensile stresses and eliminate direct mechanical attachments. McCarter has accepted these challenges and has designed and is fabricating a lightweight telescope that can replace one of beryllium at substantial savings of cost and schedule. The challenge of direct attachment has been solved with the use of bonded threaded inserts of low expansion metal. Bonding has been studied extensively as described in a companion paper, but the proprietary frit-bonding technique developed by Frank Anthony proved to be the most predictable, stable, and reliable. This technique is also used to fabricate complex components from an assembly of simpler parts. To minimize tensile stresses, the mechanical design had to be modified from the original without changing the optical prescription. This has been successfully accomplished through a "design for manufacturing" approach teaming designers, the stress analyst and manufacturing personnel. This approach has provided a design that is being produced at lower risk, lower cost and with higher predicted reliability with no loss in performance.
Silicon + Carbon = Silicon Carbide II
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Carbon-carbon mirrors for exoatmospheric and space applications
Duane E. Krumweide, Gary D. Wonacott, Patrick M. Woida, et al.
The cost and leadtime associated with beryllium has forced the MDA and other defense agencies to look for alternative materials with similar structural and thermal properties. The use of carbon-carbon material, specifically in optical components has been demonstrated analytically in prior SBIR work at San Diego Composites. Carbon-carbon material was chosen for its low in-plane and through-thickness CTE (athermal design), high specific stiffness, near-zero coefficient of moisture expansion, availability of material (specifically c-c honeycomb for lightweight substrates), and compatibility with silicon monoxide (SiO) and silicon dioxide (SiO2) coatings. Subsequent development work has produced shaped carbon-carbon sandwich substrates which have been ground, polished, coated and figured using traditional optical processing. Further development has also been done on machined monolithic carbon-carbon mirror substrates which have also been processed using standard optical finishing techniques.
Converted silicon carbide technology developments for optics
Christopher Duston, Ken Woestman, Hugo Vargas, et al.
Silicon carbide structures fabricated by converting near-net-shape graphite preforms via Chemical Vapor Conversion (CVC) phase reaction have long provided improved performance components for electronics processing. In recent years, this same technology has been applied to the fabrication of simple and lightweighted mirrors and is moving into optical bench applications. To support the expanded applications, Poco has further evaluated the material properties of SUPERSiCĀ® silicon carbide, developed technologies to mount silicon carbide mirrors on benches of similar and dissimilar materials, and fabricated complex monolithic geometries using in situ conversion bonding of mating graphite components. Overviews of each of these areas will be presented.
NTSIC: progress in recent two years
Katsuhiko Tsuno, Kazuhiko Oono, Hiroshi Irikado, et al.
New-Technology Silicon Carbide (NTSIC(R)) is a reaction sintered silicon carbide with very high bending strength. Two times higher bending strength than other SiC materials is important characteristics in an optical mirror for space application. The space optics is to endure the launch environment such as mechanical vibration and shock as well as lightweight and good thermal stability of their figure. NTSIC has no open pore. It provides good surface roughness for infrared and visible application, when its surface is polished without additional coatings. Additional advantages are in the fabrication process. The sintering temperature is significantly lower than that of a sintered silicon carbide ceramics and its sintering shrinkage is less than one percent. These advantages will provide rapid progress to fabricate large structures. Both reaction bonding method and brazing are studied in order to larger application for larger telescope. It is concluded that NTSIC has potential to provide large lightweight optical mirror.
NTSIC (new technology silicon carbide): evaluation of microstructure of high-strength reaction-sintered silicon carbide for optical mirror
Shoko Suyama, Yoshiyasu Itoh
Silicon carbide (SiC) is the most advantageous as the material of various telescope mirrors, because of high stiffness, low thermal expansion, high thermal conductivity, low density and excellent environmental stability. Newly developed high-strength reaction-sintered SiC, which has two to three times higher strength than a conventional sintered SiC, is one of the most promising candidates in applications such as lightweight substrates of optical mirrors, due to being fully dense and having small sintering shrinkage (±1 %), and low sintering temperature. In this study, in order to improve nano-scale homogeneity of the high-strength reaction-sintered SiC, the microstructure of high-strength reaction-sintered SiC was investigated using scanning electron microscopy (SEM) and microscope type interferometer in comparison with the conventional sintered SiC. And also, the microstructure was investigated by focusing on the crystal structures and the interface of each crystal through transmission electron microscopy and X-ray diffraction analysis. As a result, it was the confirmed that the high-strength reaction-sintered SiC was fully dense in comparison with the conventional sintered SiC, and the finer-scale microstructure consisted of large particles (~1 μm in diameter) of α-SiC starting powder and small particles (<1 μm in diameter) of β-SiC synthesized during the reaction-sintering (Si+C→SiC) with residual silicon (Si) filling the remaining pores. In addition, the β-SiC synthesized during the reaction-sintering was identified as the cubic type (3C), and the α-SiC of the starting powder was identified as the hexagonal type (6H).
Silicon + Carbon = Silicon Carbide III
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Fabrication and optical characterization of a segmented and brazed mirror assembly
David A. Bath, Steven C. Williams, Michel Bougoin, et al.
Direct Sintered Silicon Carbide (SSiC) is a promising material to fabricate large (over 1 meter diameter) land and space based mirror optics due to its low areal density, high stiffness and high thermal stability. To make large mirror optics for visible wavelength applications, sub-nanometer surface roughness is required, which can be achieved by cladding a SSiC substrate using SiC chemical vapor deposition (CVD). Limitations on available equipment to clad monolithic structures of this size require that smaller segments need to be clad first and then joined prior to being optically finished. To demonstrate the viability of this method of fabrication, a segmented &nullset;300mm visible quality lightweighted concave mirror has been manufactured and characterized. The mirror's 6 radial segments, coated with a SiC CVD layer on the SSiC substrate were joined by means of a silicon based braze, formulated so that its thermal expansion matched that of the SSiC substrate and SiC CVD layer. After figuring and polishing to optical quality, the mirror's stability was characterized under vacuum at three temperatures (120 K, 293 K, and 520 K) by measuring the wave front error (WFE).
Cesic and silicon: a perfect combination for high performance applications
Future novel optical systems, for example for EUV lithography and spectroscopy or X-ray applications, must achieve high optical performance, resulting in stringent requirements on stiffness and stability of the mounted optics. On the example of silicon pore optics the combination of an isotropic composite ceramic material and silicon could meet these requirements. In this paper it will be shown that especially for space applications the combination of Cesic(R) and silicon is advantageous, due to the excellent mechanical properties of Cesic(R) being used for the structural elements. This combination is especially suitable due to the match of the low coefficient of thermal expansion (CTE) between both materials. In such a way it is possible to develop, even with two different materials, a thermally stable system that can function as an optic even at cryogenic temperatures and does not require any adjustment mechanisms. This paper will discuss the material properties, present results on concrete applications for potential astrophysical science missions and show some conceptual designs and applications of this material combination for future space missions.
Manufacturing of a 3D complex hyperstable Cesic structure
Matthias Kroedel, Pascal Courteau, Anne Poupinet, et al.
Global astrometry requires extremely stable materials for instrument structures, such as optical benches. Cesic®, developed by ECM and Thales Alenia Space for mirrors and high stability structures, offers an excellent compromise in terms of structural strength, stability and very high lightweight capability, with a coefficient of thermal expansion that is virtually zero at cryogenic T°. The High-Stability Optical Bench (HSOB) GAIA study, realized by Thales Alenia Space under ESA contract, aimed to design, develop and test a full-scale representative of the HSOB bench, made entirely of Cesic®. The bench has been equipped with SAGEIS-CSO laser metrology system MOUSE1, a Michelson interferometer composed of integrated optics with nm-resolution. The HSOB bench has been submitted to a homogeneous T° step under vacuum to characterize 3-D expansion behavior of its two arms. The quite negligible interarm differential, measured with a nm-range reproducibility, demonstrates that a complete 3-D structure made of Cesic® has the same CTE homogeneity as do characterization samples, fully in line with the stringent GAIA requirements (1ppm at 120K). This demonstrates that Cesic® properties at cryogenic temperatures are fully appropriate to the manufacturing of complex highly stable optical structures. This successful study confirms ECM's and Thales Alenia Space's ability to design and manufacture monolithic lightweight highly stable optical structures, based on inner-cell triangular design made possible by the unique Cesic® manufacturing process.
Reaction bonded silicon carbide gimbaled pointing mirror
J. Robichaud, A. Akerstrom, S. Frey, et al.
A Silicon Carbide (SiC) based wide field of view Pointing Mirror Assembly (PMA) has been developed to provide two axis line-of-sight control for a fixed, space based imaging sensor. Thermal modeling has been completed in order to project the excellent thermal stability anticipated from the SiC PMA, and closed loop servo testing of the hardware has been conducted in order to quantify the bandwidth associated with line-of-sight control. In addition to the system level testing the SiC mirror substrate itself has been tested for thermal stability. We also report on results obtained with a novel polishing technique which has been applied in order to allow optical finishing of the two-phased Reaction Bonded (RB) SiC mirror substrate without the need for Silicon or SiC claddings.
SLMS athermal technology for high-quality wavefront control
The Air Force is interested in high stiffness, lightweight technologies for beam control systems. The corrected system wavefront error can be minimized using low figure error/surface finish, low print-through, high-stiffness, Silicon Lightweight Mirror Systems (SLMSTM) technology with high-reflectivity, very low absorption (VLA) coatings. We report on the fabrication of an F/1.0 mirror/mount weighing 26 pounds and with a first mode in excess of 1 kHz.
Beryllium and Metals I
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Laser generated TiC reinforced with Fe-Al matrix composite layer on Al-Si alloy
A. Viswanathan, D. Sastikumar, Harish Kumar, et al.
This paper deals with the study of Al-Si alloy laser melted with variable constituents of TiC and Fe coatings to generate TiC reinforced with Fe-Al matrix composite layer on it. This experimentation deals with the investigation of the quality of the composite layer generated by varying the process parameters and the coating composition. A superior composite layer is established when the variable processing parameters were of 2.5kW laser power and 1.5 m/min. scan speed for the coating composition of 25Fe-75TiC wt.%. This layer which consists of TiC reinforcement with Al-Fe matrix shows an average microhardness of about 750 HV and also exhibits pore and crack free surface. Bonding strength of the composite layer is also examined by the hardness test.
Cryogenic design and predicted performance of the James Webb space telescope beryllium aft optics subsystem optical bench
K. Martinez, J. Sullivan, A. Barto, et al.
With a planned launch of 2013, NASA's James Webb Space Telescope (JWST) will be the premier space observatory for astronomers worldwide. This infrared space telescope will be passively cooled to cryogenic temperatures in its solar L2 orbit. The JWST Optical Telescope Element (OTE) features a 6.5 meter, segmented Primary Mirror, which focuses light onto a Secondary Mirror and finally redirected into and through the Aft Optics Subsystem (AOS). The AOS consists of an optical bench which aligns and supports the telescope's Tertiary Mirror and Fine Steering Mirror Assemblies. This paper describes the unique cryogenic requirements and design of the JWST Beryllium AOS optical bench. Key performance requirements are reviewed including: launch environment, the cryogenic operating environment (nominally 39K), and optical alignment stability at cryogenic temperatures. The mechanical design approach utilizing Beryllium as the structural material for the AOS Bench is described relative to meeting the driving requirements. Material property verification, low and predictable material variability, and low thermal gradients across the structure are also discussed.
Beryllium optics and beryllium-aluminum structures for reconnaissance applications
Michael J. Russo, Stephen LoBiondo, Bryan Coon, et al.
BAE Systems has developed and fielded the F-9120, a compact, lightweight, dual-band Electro-Optical/Infrared (EO/IR) long range sensor for high altitude tactical reconnaissance applications. The sensor's weight and size allow it to be carried internally or in a pod on a variety of military aircraft. The challenge of maintaining optical performance over severe vibration and thermal environments has been met using beryllium optics coupled to a beryllium-aluminum structure. Material choices were vital to maintaining both the optical performance of the system over the environments as well as jitter control of the two-axis, inertially-stabilized gimbal. The beryllium and beryllium-aluminum combination has demonstrated unprecedented vibration performance in both laboratory and field environments. In addition, the close coefficient of thermal expansion (CTE) match between the optics and structure has enabled the sensor to meet its stringent imaging requirements over a wide temperature range as predicted.
Beryllium and Metals II
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Mirrors from light-weight sintered microspheres combined with replication techniques
M. P. Ulmer, S. Vaynman, M. E. Graham, et al.
This paper reviews work on fabricating light-weight optics made from inorganic composite materials. The goal of the project is to make mirrors in the 5-10 kg/m2 area density regime based on Northwestern University's previous technology used to make X-ray optics. The goal of this replication process is to end up with a smooth and also potentially accurate surface such that post figuring and polishing will not be necessary. This report covers work on fabricating witness samples up to 10 cm in diameter.
The limits of classical beam theory for bent strip residual stress measurements in plated metals
The bent strip method is often used for determining residual stresses in electroless nickel deposits for infrared mirror applications. In an earlier work the author derived the correct linear stress-strain relations for measuring residual stresses in plated metals using the bent strip method. However, the question of when bent strip specimen deflections become so large that the linear theory is no longer valid has never been clearly addressed. In this work, a preliminary analysis on the limits of the classical linear theory is carried out, and it is shown that the rotation angle in bending can be used as a good first order estimate of the linear limit. The relations between specimen bow out height and rotation angle for the bent strip method are derived, and numerical results are given for electroless nickel plated on brass, aluminum, and other mirror substrate materials.
38% Aluminum - 62% Beryllium shaped blank technology
Near-Net-Shape (NNS) technology for advanced engineered materials provides a number of supply chain benefits. These benefits include less input material, less machining hours and overall greater through put in comparison to conventional rectangular and round machining stock. Al-62%Be alloy has a unique combination of properties attractive for optical structures. It has a density of 0.076-lb/in3, 28-ksi minimum yield strength and 28-Msi elastic modulus. There have been significant developments with AlBe Hot Isostatic Press (HIP) consolidation technology in recent years. One key is using spherical AlBe metal powder which packs to a high density. The high packing density allows more complex can design and dimensional control to produce monolithic parts with isotropic properties. Other key success factors are HIP can design and the process to implement the near-net-shape strategy. This paper will describe an example of a process using shaped HIP cans to produce blanks approaching near-net-shape design through an iterative process. The strategy is to produce a seamless product to the next step in the supply chain as the iterations improve material utilization efficiency. The economic impact and planned future work will also be described.
MASTER's Session
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Materials for high-energy laser windows: how thermal lensing and thermal stresses control the performance
The engineering of high-energy lasers (HELs) for applications such as the airborne laser (ABL) system requires optical windows capable of handling megajoule beam energies. The selection of a suitable window material involves considerations relating to thermal lensing, i.e., the beam distortion caused by thermally induced phase-aberrations, in addition to issues arising from the thermal stresses generated by beam-induced temperature gradients. In this paper we document analytical methods for evaluating the impact of both beam-induced optical distortions and beam-induced mechanical stresses, which may allow the designer to properly assess the performance of window-material candidates. Specifically, thermal lensing in conjunction with planar stresses control the allowable beam fluence, whereas the two axial-stress related failure modes (thermal-shock induced fracture and yielding in compression) control the allowable beam intensity. We illustrate these considerations in the light of an evaluation of the performance of three window-material candidates for operation at the 1.315-&mgr;m wavelength. Currently, fused Si02 is the window material of choice for contemplated HELs operating in the near infrared; it is, however, vulnerable to optical distortion, which renders this material unsuitable for applications that require transmitting large beam fluences. On assuming that stress-birefringence is of no concern, oxyfluoride glass outperforms Si02, but evidence of a poor thermal conductivity degrades this material's ability to transmit high-intensity beams. Fusion-cast CaF2 emerges as the most promising "compromise" solution in the sense that this material combines superior optical features with acceptable thermomechanical properties; in effect, CaF2 windows easily meet requirements as formulated for the first-generation ABL system.
Optomechanical design, engineering, and assembly: 60 years of evolution
We recall how techniques for optical and mechanical design, engineering and fabrication have evolved during the 60-year period since the end of World War II. Considerations include some ways in which improvements in materials availability and in methods for design, analysis, tolerancing for fabrication and alignment, and hardware assembly, inspection and environmental testing may have facilitated development of increasingly sophisticated optical instruments.
Poster Session
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Theoretical analysis for double-liquid variable focus lens
Runling Peng, Jiabi Chen, Songlin Zhuang
In this paper, various structures for double-liquid variable focus lens are introduced. And based on an energy minimization method, explicit calculations and detailed analyses upon an extended Young-type equation are given for double-liquid lenses with cylindrical electrode. Such an equation is especially applicable to liquid-liquid-solid tri-phase systems. It is a little different from the traditional Young equation that was derived according to vapor-liquid-solid triphase systems. The electrowetting effect caused by an external voltage changes the interface shape between two liquids as well as the focal length of the lens. Based on the extended Young-type equation, the relationship between the focal length and the external voltage can also be derived. Corresponding equations and simulation results are presented.
Cryogenic performance of piezo-electric actuators for opto-mechanical applications
Space telescope designs driven by science goals such as the infrared observation of high-redshift galaxies and the infrared observation of objects that would otherwise be obscured by dust in the visible push the operating temperatures of the optics to cryogenic temperatures. Typical temperatures, 30 to 100 K are a challenging regime for actuators, but little information is available on the low-temperature performance of Piezo-electric actuator products currently on the market. Work is underway to measure actuator stroke and CTE, at low temperatures for typical PZTs, such as those available "off-the-shelf" from P.I. and Thorlabs.