This paper discusses the design and fabrication of ultra lightweight laser scanning mirrors from two types of metal-matrix composites for the next generation Space Vision System (SVS). The materials selected for this study were SiC particulate reinforced aluminum composite and beryllium-aluminum (AlBeMet) composite. Three mirror designs were made and compared in terms of mass, rotating inertia and first mode natural frequency. Mirror surface layer selection and processing were discussed. Problems encountered during the mirror fabrication and the ways to solve it were presented.

In the light of the recent successes in utilizing CFRP composites for fabrication of ultra-lightweight, micron- accuracy reflectors for space telescopes, this paper provides a recent assessment of the main factors influencing dimensional stability of composites. Two recent examples of all-composites reflector designs that demonstrate the validity of the composites choice for this type of space applications are presented.

Our group at the University of Colorado has built a prototype interferometer that demonstrates x-ray fringes. We briefly describe how the instrument works and its geometry, and then present a detailed optical tolerance analysis. Careful analysis shows a grazing incidence design provides enough tolerance relaxation for our x-ray interferometer to work. The challenging nature of x-ray alignment has led us to a methodology that employs a succession of decreasing wavelengths. We also present fringe optimization methods and address environmental conditions that affect stability.

Evaluation of the optical performances of bimetallic mirrors with various substrate shapes was conducted using the finite element analysis program, SDRC-IDEAS. In these analyses, two different plating materials, nickel and aluminum were considered for an aluminum and a beryllium mirror substrate. Thermal environment used in this study is a unit thermal soak. Surface errors, individual aberration terms, such as piston, tilts, focus and other aberrations were obtained by the program PCFRINGE. It was found that the optical performances of bimetallic mirrors depend on the polating material, plating thickness, and the mirror substrate shapes materials. The optimum plating thickness combinations were determined based on plating material and mirror substrate with temperature difference. The results were compared with the optical surface errors and the corrected surface errors. The results indicate that there does not exist a definitive common rule for the optimum, but a detailed analysis such as presented herein is generally needed to design bimetallic mirrors in a thermal environment.

A novel technology to fabricate ultralightweight mirrors was demonstrated. High thermal conductivity C-C composite integrated honeycomb face sheets were fabricated using a tape layup. Chemical Vapor Deposition (CVR)-SiC was employed to produce a functionally graded transition in CTE from about 0 ppm/K to about 4.5 ppm/K. A crack free CVR-SiC surface was achieved which was subsequently polished. A 1 kg/m2 SiC mirror structure was demonstrated.

By combining the excellent intrinsic thermo-mechanical properties of the silicon carbide (SiC) with a structural design based on a sandwich structure composed of two SiC face sheets deposited on a foam core of the same material, it is possible to manufacture very light and stiff mirrors for space applications. This paper presents some results of a technological development study, including the realization of a lightweight athermalized SiC telescope with a 310 mm diameter foamed-SiC primary mirror. An ion beam figuring equipment has been developed to improve the optical quality of the mirror.

Numerical techniques for a class of optimization problems associated with the thermal modeling of optomechanical systems are presented. Emphasis is placed on applications where radiation plays a dominant role. This work is motivated by the need for incorporating thermal analysis into integrated modeling of high-precision, space-borne optical systems. The specific problems of interest are thermal control to minimize the wavefront error by application of external heat loads, and the temperature estimation problem of predicting temperatures at arbitrary nodes of the model given noisy measurements on a subset of nodes. The proposed numerical techniques are briefly described and compared to existing algorithms. Their accuracy and robustness are demonstrated through numerical tests with models form ongoing NASA missions.

This paper discusses NASTRAN finite element analysis of the Sub-scale Beryllium Mirror Demonstrator (SBMD), which has been developed by Ball Aerospace as an experimental lightweight (9.76 kg/m2 areal density) design concept for the Next Generation Space Telescope (NGST). The mirror was repeatedly subjected to a 30 K environment in the large cryogenic test chamber at Marshall Space Flight Center (MSFC). Deformations on the mirror surface were measured optically. The surface distortions predicted by NASTRAN were analyzed for comparison with the measured values. Model results compared more favorably with measured results for the ambient temperature cases. For the cryogenic cases, the influence of geometry and material property variations was investigated to obtain closer correlation.

In an effort to get larger primary mirrors for both space and ground-based telescopes, many proposed designs are either segmented or adaptive or both. This paper discuses many practical analysis issues concerning the prediction of performance of these large mirrors. Topics include 1) correctability with and without focus control, 2) dynamic response analysis, 3) segment pointing and surface RMS.

The ninety-one 1 m mirror segments which comprise the McDonald Observatory Hobby-Eberly Telescope (HET) primary mirror have been observed to drift out of alignment in an unpredictable manner in response to time variant temperature deviations. A Segment Alignment Maintenance System (SAMS) is being developed to detect and correct this segment-to-segment drift using sensors mounted at the edges of the mirror segments. However, the segments were not originally designed to carry the weight of edge sensors. Thus, analyses and tests were conducted as part of the SAMS design to estimate the magnitude and shape of the edge sensor induced deformations as well as the resultant optical performance. Interferometric testing of a 26 m radius of curvature HET mirror segment was performed at the NASA/Marshall Space Flight Center using several load conditions to verify the finite element analyses.

The twin composite structure telescopes aboard the Microwave Anisotropy Probe were selectivity roughened to reduce focused solar radiance. They were then overcoated with evaporated A1 + reactively evaporated silicon oxide films whose respective thicknesses were sufficient to achieve the high reflectance of bulk aluminum at the microwave operating frequencies; high emittance in the thermal emittance region; and moderately low solar absorptance for a resultant (alpha) /(epsilon) < 0.9. This report will discuss the experimental techniques used to prepare the telescope reflector surfaces and to evaluate their resultant properties.

This paper presents structural and thermal modeling of a high-performance CCD camera designed to operate under severe environments. Minimizing the dark current noise required the CCD to be maintained at low temperature while the camera operated in a 70 degrees C environment. A thermoelectric cooler (TEC) was selected due to its simplicity, and relatively low cost. Minimizing the thermal parasitic loads due to conduction and convection, and maximizing the heat sink performance was critical in this design. The critical structural features of this camera are the CCD leads and the bond joint that holds the CCD in alignment relative to the lens. The CCD leads are susceptible to fatigue failure when subjected to random vibrations for an extended period of time. This paper outlines the methods used to model and analyze the CCD leads for fatigue, the supportive vibration testing performed and the steps taken to correct for structural inadequacies found in the original design. The key results of all this thermal and structural modeling and testing are presented.

Telecommunication wavelength division multiplexing systems (WDM) demand high fiber-to-fiber coupling to minimize signal loss and maximize performance. WDM systems, with increasing data rates and narrow channel spacing, must maintain performance over the designated wavelength band and across a wide temperature range. Traditional athermal optical design techniques are coupled with detailed thermo-elastic analyses to develop an athermal optical system under thermal soak conditions for a WDM demultiplexer. The demultiplexer uses a pair of doublets and a reflective Littrow-mounted grating employed in a double-pass configuration to separate nine channels of data from one input fiber into nine output fibers operating over the C-band (1530 to 1561.6 nm). The optical system is achromatized and athermalized over a 0 degrees C to 70 degrees C temperature range. Detailed thermo-elastic analyses are performed via a MSC/NASTRAN finite element model. Finite element derived rigid-body positional errors and optical surface deformations are included in the athermalization process. The effects of thermal gradients on system performance are also evaluated. A sensitivity analysis based on fiber coupling efficiency is performed for radial, axial, and lateral temperature gradients.

A fiber optic spread-spectrum encoder has ben analyzed for thermal stability using the optomechanical constraint equations as a modeling tool. The equations were implemented in a computational spreadsheet and coupling efficiency was computed for temperatures between room ambient and 20 degrees C above ambient. The analysis results compared favorably with engineering tests. Design changes were identified that would greatly improve the thermal stability of the encoder system.

Several performance factors such as spectral properties, hardness, thermal stability, glass transition temperature, and out-gassing need to be taken into consideration when selecting an appropriate adhesive. Optical applications require that the selected adhesive not only assure mechanical integrity of the assembled element but also support its optical performance. This paper discusses how to select an adhesive for some common optical applications and also demonstrates the use of analytical methods in the metrology of optical adhesives.

To enable the invention of higher power IRCM lasers, 3D LIDAR systems, Designator/Rangefinders and other Instruments subjected to a broad range of operating conditions, there is a need to develop improved technology to hold small mirrors, lenses, beamsplitters and other optical elements with repeatable and high dimensional stability over wide environmental temperature ranges, an do so with great economy. The intent of this effort was to begin identifying significant factors for bonding small mirrors for high stability. A screening experiment was performed in which half-inch diameter flat mirrors were face bonded to similar mirror mounts, then bolted to a reference test fixture and subjected to an environmental temperature range of -40 to +70 degrees C. Mount material, optic material, adhesive material, bond joint design, and bond thickness were varied. The resulting tilt errors in the mirror assemblies were measured. Steps were taken to isolate the bond joint stability as opposed to stability in the mounted mirror subassemblies. The effort required to minimize experimental noise was much greater than anticipated. This first experimental effort failed to identify main factors with statistical significance, however; some results are interesting. Perhaps also of interest is the progress made at characterizing the experimental setup and process, and lessons learned in control of noise factors in this kind of experiment.

With so many new adhesives available, characteristics affecting performance are not always well-defined. The user often selects an adhesive based on a single property and later finds his application compromised. This is an effort to study relevant properties of several different structural-type adhesives. The bonding geometry will utilize three types of glass bonded to metal mounts. The mounting geometry will include five different design approaches. These designs will investigate: face bonding, counter-bored mounts, edge bonding, and a flexure mount. The three metals selected are not only common to the industry but often used for matching the Coefficient of Expansion to the optical glass. Each optical flat will have its reflective surface used as a reference for angular stability. The adhesives selected will compare more traditional epoxies with one-part UV light cured products. The obvious advantage of the UV- cured adhesives is the instant cure on-demand. Several adhesives have been selected for differing properties including: viscosity, cure temperature, CTE, modulus of elasticity, out-gassing, and shrinkage upon cure. Discussion will compare each adhesive, its properties, and ease of use. Angular stability will be monitored as a function of: pre vs. post cure, accelerated life testing, thermal exposure, and vibration/shock exposure. Some discussion will be included on the wavefront distortion and stress birefringence.

This paper describes the development of a new family of light curing adhesives containing a new reactive additive previously not used in optical grade light curing adhesives are obtained with the addition of functionalized cellulositics. Outgassing as low as 10^-6 grams/gram has been observed based on headspace sampling. Other additives have lowered the shrinkage rates of positioning adhesives from near 1 percent to less than 0.1 percent with fractional, percentage movements over thermal range of -40 degrees C to +200 degrees C.

As tactical military lasers become more complex and the requirement for effectiveness increases, the stability of the optics comprising those lasers becomes critical. Boresight stability requirements for individual optomechanical subassemblies are in the sub-100 microradian range with temperature excursions of up to 80 degrees C. Even the most detailed Finite Element Modeling is ineffective in predicting performance to the accuracy and resolution required. Boresight error allocations of individual optical subassemblies must be verified with test. Boresight tests were performed on several optical subsystems of a military laser required to hold boresight in an airborne military environment. The units tested were fabricated and assembled using the materials and processes prescribed for production. The purpose of the testing was to verify that the subsystems do not exceed their allocated stability tolerance. The results show angular shift in azimuth and elevation over a temperature range of -54 to +71 C. Assembly of the units was performed at approximately 23 degrees C.

The Herschel Space Observatory (formerly known as FIRST) consists of a 3.5 m space telescope designed for use in the long IR and sub-millimeter wavebands. To demonstrate the viability of a carbon fiber composite telescope for this application, Composite Optics Incorporated (COI) manufactured a fast (F/1), large (2 m), lightweight (10.1 kg/m2) demonstration mirror. A key challenge in demonstrating the performance of this novel mirror was to characterize the surface accuracy at cryogenic (70 K) temperatures. A wide variety of optical metrology techniques were investigated and a brief survey of empirical test results and limitations of the various techniques will be presented in this paper. Two complementary infrared (IR) techniques operating at a wavelength of 10.6 microns were chosen for further development: (1) IR Twyman-Green Phase Shifting Interferometry (IR PSI) and (2) IR Shack-Hartmann (IR SH) Wavefront Sensing. Innovative design modifications made to an existing IR PSI to achieve high-resolution, scannable, infrared measurements of the composite mirror are described. The modified interferometer was capable of measuring surface gradients larger than 350 microradians. The design and results of measurements made with a custom-built IR SH Wavefront Sensor operating at 10.6 microns are also presented. A compact experimental setup permitting simultaneous operation of both the IR PSI and IR SH tools is shown. The advantages and the limitations of the two key IR metrology tools are discussed.

The Herschel Space Observatory (formerly known as FIRST) consists of a 3.5 m space telescope. Stitching sub aperture interferograms may offer considerable cost savings during testing of the flight telescope as compared to other techniques. A comparative demonstration is presented of interferogram stitching techniques that enable a composite map of a 3-D surface to be assembled from a sequence of sub-aperture measurements. This paper describes the fundamental procedures for stitching together component data sets and demonstrates such techniques with real data sets. A set of 14 sub-aperture measurements was made of a 2 m diameter all-composite mirror developed as part of the Herschel Space Observatory program and two different stitching software packages were employed to stitch together the sub-aperture surface maps. The software packages differ fundamentally in the way the sub-aperture maps are three-dimensionally stitched, one employing a local technique and the other using a global technique. The processed results from both algorithms are compared with each other and with a full-aperture reference measurement made of the same test optic. A summary of the results is presented and potential modifications and enhancements to the stitching techniques are discussed.

The Herschel Space Observatory (formerly known as FIRST) consists of a 3.5 m space telescope. As part of a JPL- funded effort to develop lightweight telescope technology suitable for this mission, COI designed and fabricated a spherical, F/1, 2 m aperture prototype primary mirror using solely carbon fiber reinforced polymer (CFRP) materials. To assess the performance of this technology, optical metrology of the mirror surface was performed from ambient to an intended operational temperature for IR-telescopes of 70K. Testing was performed horizontally in a cryogenic vacuum chamber at Arnold Engineering Development Center (AEDC), Tennessee. The test incorporated a custom thermal shroud, a characterization and monitoring of the dynamic environment, and a stress free mirror mount. An IR-wavelength phase shifting interferometer (IR PSI) was the primary instrument used to measure the mirror surface. From an initial surface figure of 2.1 microns RMS at ambient, a modest 3.9 microns of additional RMS surface error was induced at 70K. The thermally induced error was dominated by low-order deformations, of the type that could easily be corrected with secondary or tertiary optics. In addition to exceptional thermal stability, the mirror exhibited no significant change in the figure upon returning to room temperature.

The effects of specific aberrations on the optical performance of the all-composite design for the Herschel Space Observatory are examined. A review of the all-composite design for the large aperture (3.5 m) telescope that satisfies the target specifications is presented. Cyrogenic experiments with a carbon fiber reinforced polymer (CFRP) 2 m demonstration mirror have yielded empirical bounds on the high- and low-order spatial frequency aberrations that will be anticipated in the full 3.5 m Ritchey-Chretien telescope design. Detailed analysis is presented on the effect of the low order aberrations of the primary mirror on the system wavefront error and encircled energy. Predictable limits of correction via low order shaping of the secondary mirror are described. The impact of higher order surface errors on the encircled energy and the stray light will also be presented. Comments are made regarding the impact of the optical prescription and CRFP design on flight telescope testing.

Two previous papers treated a general purpose optomechanical system in which optical elements are mounted in cylinders that are located in Vs. The present paper presents several applications of this system. Knowledge of the first two papers is assumed.

The Fiber Optic Respiratory Plethysmograph (FORP) is a non-invasive instrument for respiratory and heart monitoring in humans, based on the design of the Respiratory Inductive Plethysmograph (RIP. The FORP uses two sensors at thoracic and abdominal levels that measure circumferences rather than the cross sectional areas measured by the RIP. Each sensor is made of a specifically looped optical fiber that responds to elongation with variation in light transmission, via the macrobending loss effect. The design and construction of the original version of the FORP has been reported previously 1. This paper presents the results of a new figure-of-eight construction for the fiber loops. The resulting system shows greater signal range, increased linearity and less hysteresis than former constructions. Results are presented detailing the calibration of the respiratory measurements against a spirometer using a range of calibration protocols, one based on isovolume breathing and others on a Least Mean Square (LMS) fit. Additional improvements to signal processing and the increased sensitivity of the new design now make it practicable to detect torso motion arising from cardiac activity. This paper also presents results showing the simultaneous monitoring of respiratory and cardiac signals, using only the FORP transducers.

ONERA has developed an IR camera prototype named CRYSTAL to perform surface flow visualization at cryogenic temperatures in the severe environment of ETW GmbH. The camera, which has been operating since 1998, is based on a 128 X 192 Si:Ga focal plane array and is, to our knowledge, the first world- wide IR camera to work in a cryogenic wind tunnel and at such temperatures. Indeed, the working temperature of the tunnel varies between 313 K and 90K. The qualitative thermometry of CRYSTAL from the ambient reaches down to 120 K. The aerodynamic effects to observe need a level of resolution inferior to 1 K. This paper addresses the mechanical aspects of the instrument.

One of the critical design factors for large telescopes is control of primary mirror distortion caused by wind pressure variations. To quantify telescope wind loading effects, the Gemini Observatory has conducted a series of wind tests under actual mountaintop conditions. During commissioning of the southern Gemini Telescope, simultaneous measurements were made of pressures at multiple points on the mirror surface, as well as wind velocity and direction at several locations inside and outside the dome. During the test we varied the dome position relative to the wind, the telescope elevation angle, the position of windscreens in the observing slit, and the size of the openings in the ventilation gates. Five-minute data records were made for 116 different test conditions, with a data-sampling rate of ten per second. These data sets have been processed to provide pressure maps over the surface of the mirror at each time instant. From these pressure maps, the optical surface distortions of the primary mirror have been calculated using finite-element analysis. Data reduction programs have been developed to enhance visualization of the test data and mirror surface distortions. The test results have implications for the design of future large telescopes.

A dual field of view IR lens system that incorporates motorized mechanical movement in a compact package is presented. A feature of the design is to change the field of the lens system in less than one second. A secondary goal of the system is to maintain a low overall system profile. Attention is given to the task of identifying a candidate motor for the system. Some commonly encountered pitfalls in the design process are identified.

Non-mechanical beam steering technologies, utilizing acousto-optics, allow for achieving the high bandwidth laser beam positioning required for optical communications, laser scanners, LADARs, etc. Properties of the Bragg cell, chiefly responsible for the efficiency and attainable characteristics of the entire positioning system, are assured by successful design of this optical component. However, design of Bragg cells is dominated by experience and intuition of the designers and the potential of this technology is not fully utilized. An optimal design problem of a Bragg cell is formulated on the basis of known equations of the underlying physical phenomena, and a genetic optimization scheme is applied for the solution of the resultant formidable problem. The approach not only yields a design solution, but also allows for the variation of the design criterion and emphasizing particular properties of the resultant component. The prowess of the proposed approach has been demonstrated by design optimization examples.

For production line manufacturing of Scanning Seekers, the optical train set-up, assembly, alignment and buy-off of optical parameters requires utilization of an automated Optical Test Bench by trained operators. Adjustment of the optical elements to obtain the specified seeker parameters, such as scan-diameter and focus, can be a time consuming iterative process if test errors and techniques of the test bench are not within sufficient accuracy limits of the end product specification. The periodic calibration of the opto- mechanical components is essential to ensure that all aspects of the test system are traceable to standards and the equipment itself has not become inflicted with random measurements errors. This paper covers the development of calibration limits and adjustment tolerances for an optical test bench using the methods of Influence Functions, analysis Code V² and addressing the limitations of optical bench components.

The Airborne Digital Sensor (ADS) a development to fulfil photogrammetric and remote sensing requirements. The new digital sensor is not only a camera for pretty nice pictures. It will be the next - full digital - generation as a measurement device for airborne photogrammetry and remote sensing. The high accuracy design of the focal plane system under flight and environmental conditions (pressure and temperature) will be presented. The ADS project will be introduced as a design of a modular customized CCD line scanner concept. It will be discussed on the ADS version with 4 multispectral CCD lines and 3 panchromatic CCD lines. The presentation will gives an overview of all dependencies and design constrains on the ADS Focal Pate Module (FPM). The ADS optical system has to support both photogrammetric accuracy and the requirement on the SNR for remote sensing applications. The principle to achieve good color pixel matching is described in relation to the customized CCD- and FPM- design. After a short description of the technical design and performances, some application examples are shown to demonstrate the main features of digital sensor: high accuracy, wide angle, high radiometric dynamics, high signal-to-noise-ratio, in-track stereo capability, multispectral capability.

The main optical system of Space Solar Telescope is composed of primary mirror, collimating lenses and imaging lenses. To satisfy imaging demands of wide range of wavelength (393nm- 656nm), the collimating lenses are composed of five components of which decentering errors are extremely stringent. To satisfy above situation, elastomeric mounting of lens is introduced for each component. The basic centering principle is discussed, the subcell assembly is introduced for the elastomeric mounting. Two aligning methods of are introduced for the alignment of subcells. Athermalization formulation of subcells is given. Besides, finite element model of such mounting is established for analyzing temperature change and elastomer shrinkage effects to lens surfaces.

A precision positioning system with a high displacement resolution has been widely required for modern industrialized applications, such as microelectronics, super-precision manufacturing etc. This paper discusses the design and the features of a new piezo driven precision micro positioning stage utilizing flexure hinges. Theoretical analysis for the stiffness of the flexure hinge is also given briefly. A piezoelectric ceramic is applied to drive the precision state, whose displacement can reach 5 micrometers when employed with 1000 voltage power. In order to testify the robust and measurement stability of the precision sta, three kinds of PZT produced in Germany, Japan and China respectively are utilized. A dual-frequency interferometer with nanometer resolution and accuracy is adopted to evaluate the mechanical characteristics of the positioning stage. The experimental result shows that the open loop control of the stage provides 0.2nm positioning resolution along the moving direction.

A kind of bireflectance thin film on the window plate of a 633nm He-Ne laser is presented in this paper. The film of non quarter-wave-stack is coated on the substrate with the application of external load on it. The load on the substrate is removed after the coating has been accomplished, then the strain on the substrate will transfer to the multilayer film. Due to photoelastic effect, the multilayer film becomes an anisotropic film. Selecting appropriate film structure and suitable center wavelength, a high phase dispersion with a nearly constant reflectivity will be obtained around the working wavelength. For normal incidence, a phase shift difference between the two orthogonal polarization states of the reflected wave will produce. As a result, a dual-frequency laser with a beat frequency of 4-5 megahertz can be carried out by using this kind of bireflectance thin film. Based on this principle, a He-Ne dual-frequency laser equipped with bireflectance cavity mirror is described. The model coupling is reduced by utilizing transverse Zeeman effect so that two linear and orthogonal polarization components with 5MHz beat frequency are generated. The effect of the magnetic field's direction on the dual-frequency as well as the polarization property of the laser are investigated by experiments. After stabilizing the frequency, the laser is calibrated with the iodine frequency stabilization laser at Chinese National Institute of Metrology. Experimental results indicate that the expanded uncertainty of wavelength in vacuum is 1 X 10^-7 with the frequency stabilization of 6.6 X 10^-10.

The Integrated Optical Design Analysis (IODA) program is a software tool being developed to support concurrent engineering design of complex optical systems. IODA provides seamless data fusion between thermal, structural, and optical models used to design the system. The software architecture was developed by reviewing current design processes and developing software to automate the existing procedures. IODA significantly reduces the design iteration cycle time and eliminates many potential sources of error.

We describe a new mounting technique for rapid alignment using semi-kinematic (SK) rails. Features of the technique include structures for positioning lens elements, beam splitters, mirrors, and the like. The SK rails are less complicated to machine than traditional v-groove technology.