Large-aperture lightweight space mirrors are critical for NASA space science missions. But, a technology gap exists between the current state-of-art and the optics required to enable planned missions (SAFIR, SUVO, MTRAP, TPF). Building on the highly successful JWST technology development program, a new unified sustained effort is required for these future missions. This effort’s objectives are to develop enabling mirror technology and to reduce cost & schedule. The ultimate goal is to return $10 of savings for each dollar invested. This paper summarizes the optic needs for several planned NASA missions and describes a technology development roadmap.

In the modern optical shop, technicians are typically skilled machine operators who work on only one phase of the manufacture for each and every component. The product is designed, specified, methodized, scheduled and integrated by people off the shop floor. Even at the component level, the people inside the shop usually see only one stage of completion. In an effort to make the relevance of their work visible; to demonstrate competence to their peers; to gain appreciation for the work of others; and to give them a meaningful connection with the functions of optical systems, I created “The Telescope Project” for my former employer. I invited those interested to participate in an after-hours, partially subsidized project to build telescopes for themselves. The ground-rules included that we would all make the same design (thus practicing consensus and configuration management); that we would all work on every phase (thus learning from each other); and that we would obtain our parts by random lot at the end (thus making quality assurance a personal issue). In the process the participating technicians learned about optical theory, design, tolerancing, negotiation, scheduling, purchasing, fabrication, coating and assembly. They developed an appreciation for each other's contributions and a broader perspective on the consequences of their actions. In the end, each obtained a high-quality telescope for his or her personal use. Several developed an abiding love for astronomy. The project generated much interest from technicians who didn’t initially choose to participate. In this paper I describe the project in detail.

The Precessions process for producing aspheric and other optical surfaces is undergoing rapid development. In this paper, we summarise the considerable success achieved in controlling the repeatability of the process on both the 200mm and 600mm machines, and illustrate this with examples of aspherics that have been produced. We particularly describe our approach to fine form-control. This has required the development of various strategies to moderate the volumetric removal rates, in order to give the required sensitivity of removal. We conclude with a discussion of the scaling laws that apply when adapting the process to smaller and larger sized parts. This is illustrated by predicting the process-parameters for mass-producing segments for extremely large telescopes.

We describe an inverse numerical procedure that allows the analysis of scratches in brittle materials often used in optics manufacturing. The analysis assumes that materials deform by elastic/plastic mechanisms, i.e. no cracking, and that scratches are caused by spherical abrasives. As inputs we use the measured depth and width of surface scratches, and the micromechanical properties (elastic modulus, hardness, Poisson ratio) of the material surface. The outputs of the numerical procedure are estimates of the abrasive size and abrasive force (load) that caused the scratch in question. Materials we have examined to date are fused silica (FS), borosilicate glass (BK7), laser phosphate glass (LHG8), silicon (Si), and calcium fluoride (CaF₂). The inverse analysis also may be used to answer the question: What must the abrasive size and load be in order to produce scratches shallower in depth and narrower in extent than a given design requirement?

The possibilities of iTIRM, an in-process surface measurement tool, are explored in this research. Experiments are done to test the applicability for qualifying and optimizing finishing processes for optical surfaces. Several optical glasses, different polishing agents and ductile grinding are included in these experiments. It is concluded that iTIRM can be used for both mentioned applications but that it is, at least for now, an R&D tool only and not applicable in production.

Aluminum oxynitride (ALON) is a polycrystalline material that has proven difficult to polish due to its grain structure. Bound abrasives are an effective means for polishing ALON, and work is being done with them to obtain good surfaces, with reasonable removal rates. Laps consisting of abrasives bound in epoxy matrices were created for polishing ALON. The effects of varying abrasive type, abrasive concentration, lap shape, coolant and load were studied. Metrology procedures were developed to monitor different aspects of the grain structure and numerically evaluate grain boundary decoration. Strategies were developed to polish ALON at acceptable rates with reasonably good surface quality. Work is directed toward finding optimal bound abrasive lap formulations that can be fabricated into ring and/or contour tools for testing on CNC machining platforms.

Organic nonlinear optical crystal 4-dimethylamino-N-metyl-4-stilbazolium tosylate (DAST) can be used for new optical devices such as high frequency electro-optical sampling wavelength conversion, submillimeter wave generation, and terahertz-wave generation. The crystal is soft, brittle and hygroscopic so that it is very difficult to get optical surfaces by using conventional optical polishing process. This paper deals with single-point diamond turning for getting optical surfaces on DAST crystals. Three typical planes on DAST crystals were finished by single-point diamond turning. The quality of single-point diamond turned surface depends upon the crystallographic plane, cutting direction, cutting speed, depth of cut, feed rate, rake angle, nose radius of diamond tool, tool clearance angle, tool wear, lubricant and its supplying method. The turned surface was measured with a Nomarski interference microscope, atomic force microscope, and a three-dimensional optical profiler. By optimizing the machining conditions, 0.33 nm rms surface roughness and 8.7 nm p-v flatness in 1 mm square were obtained on a b-plane of DAST crystal.

Modern synchrotron radiation sources of the 3rd generation like BESSY II, Spring-8 and others with their high brilliance beam characteristics need very high quality optics to exploit the full power of this radiation. For the grazing incidence reflecting type of that optics (flat, spherical or aspherical) besides roughness the slope deviation error is the most important spec, which has to be improved to meet the present and future performance requirements. Together with partners from industry we investigate and develop on the one hand surface figuring and polishing techniques for final finishing by using mainly ion beam milling technology and on the other hand we improve and make use of the combination of the surface shape measurements by means of interferometry, long trace and auto-collimation profilometry. We aim to achieve the following slope deviation errors on silicon optical elements: flat surface 310 mm long 0.03 arcsec rms, flat surface 100 mm long 0.02 arcsec rms and elliptical cylinder surface 210 mm long 0.1 arcsec rms. This is a five to ten-fold improvement compared to the present state of the art in production. To achieve the demanding specification it is necessary to measure and to deterministically machine the surface over a wide range of spatial wavelength down to the sub-millimeter range. In depth scale the sub-nanometer shape error level has to be achieved. The roughness of about 0.2 nm rms has not to be increased during the shape finishing.

Diffraction gratings can be manufactured in a large variety of ways depending on the required grating characteristics. In this work we have concentrated on surface relief gratings etched into large blocks of silicon with a polished surface. The applications for this kind of gratings are for mirrors and monochromators in the beam-line of a synchrotron. This application requires gratings with sub 100 nm etching depths -- in some cases even sub 10 nm -- with a very high control of the grating period and etching depth over the entire gratings ranging from 90 mm x 30 mm to 200 mm x 30 mm with useful areas from 80 mm x 10 mm to 190 mm x 10 mm. In some cases there are two grating tracks with different structure design on the same Si substrate. In this work we have shown that a combination of holographic exposure in a standard photo-resist and ion beam etching with a dwell time mode using a sub-aperture gaussian shaped removal function is an excellent fabrication procedure to meet the tight tolerances for this special type of gratings. We fabricate gratings for spectral ranges from 10 - 20 eV to 1000 - 2000 eV with etching depths ranging from 100 nm to a few nm and characterize them thoroughly by Atomic Force Microscopy.

Calcium Fluoride roughness evolution caused by ion beam milling has been studied in dependence on the ion milling parameters and different optically polished surfaces, respectively. For polished surfaces with high crystal damage, the roughness is dominated by the uncovering of the sub-surface damage due to the ion beam milling. For smooth surfaces with low damage the roughness is an intrinsic one and the creation of self-organized nanoscale structures can be obtained. Ion milling parameters influence more the intrinsic roughness than the extrinsic. Generally, high ion energies and sputter gases with low atom mass produce rough surfaces. Low ion energies and gases with high mass result in smooth surfaces. Ion bombardment induces a decomposition of CaF₂ in the near surface layer. Surface analytical measurements show that ion sputtering to some extent decompose the CaF₂ surface layer in contrast to the combined action of ion sputtering and low energy electron irradiation. The measured higher VUV absorption after ion milling is caused by the modified sub-surface layer mainly and not by the increased surface roughness.

A variation on the fluid jet polishing (FJP) technique, arbitrarily named Jules Verne (JV), will be described in this article. Jules Verne is a glass processing technique that removes material due to the fact that the tool and the surface are in close contact, and a slurry moves in between the tool and the surface. This approach has both advantages and disadvantages with respect to the original FJP modus: it enables a feed-controlled machining process, but deeper lying areas are harder to reach. A simulation model will be presented that predicts the flow of the slurry in the Jules Verne setup, which is followed by the computation of the trajectories of the particles in the flow. Furthermore, experimental data will be reported demonstrating the feasibility of the JV idea. A model will also be presented simulating the interaction between the surface and the impinging abrasives at a microscopic level, enabling the prediction of the final surface roughness.

A polishing robot, using the fluid jet polishing technique (FJP), in combination with in-situ monitoring systems will be presented. One of the monitoring systems is used to check the surface roughness, while the other checks the local removal. Owing to this removal monitoring system the presented system is ideally suited for corrective polishing applications where normally a time consuming iterative approach would be required.

It has been shown that a magnetically stabilized round jet of MR polishing fluid generates a reproducible material removal function (polishing spot) at a distance of several tens of centimeters from the nozzle. As a polishing technique, this unique tool resolves a challenging problem of high precision finishing of steep concave surfaces and cavities. Theoretical prerequisites and experimental results are discussed.

The magnetorheological finishing (MRF) process makes use of a magnetically stiffened magnetorheological abrasive fluid to polish the surface of a workpiece in a precise fashion. The process may be used to finish the surface of high quality optical lenses. Investigations have been undertaken to quantify the operation of MRF and to identify those parameters key to an optimal operation of this lens production process. A correlation has been developed to relate the parameters important to the removal characteristics and to the precision of the polishing result and to the duration of polishing. A relationship to indicate the most appropriate MRF processing parameters for a lens is presented. In the examples discussed Fringe-Zernike polynomials are used to quantify the error on a lens.

Magnetorheological finishing (MRF) was used to polish as-molded or diamond turned surfaces of several optical polymers. Materials included polymethylmethacrylate (PMMA), cyclic olefin polymer (COP), polycarbonate (PC), and polystyrene (PS). Parts were nominally plano circular discs of various diameters (~40 mm to 75 mm) and thicknesses (2.5 mm to 25 mm). Polishing trials were conducted with standard CeO₂-based and nanodiamond-based MR fluids, or with MR fluids containing SnO₂, ZrO₂, Al₂O₃, TiO₂, or SiO₂. Excellent results were obtained for PMMA using a ZrO₂-based MR fluid. The diamond turned plano surface of a 38-mm diameter by 8-mm thick puck was improved from an initial p-v wave front error of 4.5 µm to 0.35 µm with two figure correction runs. The average rms surface roughness was reduced from 3.8 nm to 0.47 nm, and the diamond turning marks were eliminated. Mounting and thermalization of polymer parts for in-process and final metrology was found to be a challenge.

The manufacturing design and process development for the Visor for the JHMCS (Joint Helmet Mounted Cueing System) are discussed. The JHMCS system is a Helmet Mounted Display (HMD) system currently flying on the F-15, F-16 and F/A-18 aircraft. The Visor manufacturing processes are essential to both system performance and economy. The Visor functions both as the system optical combiner and personal protective equipment for the pilot. The Visor material is optical polycarbonate. For a military HMD system, the mechanical and environmental properties of the Visor are as necessary as the optical properties. The visor must meet stringent dimensional requirements to assure adequate system optical performance. Injection molding can provide dimensional fidelity to the requirements, if done properly. Concurrent design of the visor and the tool (i.e., the injection mold) is essential. The concurrent design necessarily considers manufacturing operations and the use environment of the Visor. Computer modeling of the molding process is a necessary input to the mold design. With proper attention to product design and tool development, it is possible to improve upon published standard dimensional tolerances for molded polycarbonate articles.

The Wilkinson Microwave Anisotropy Probe (WMAP) measures anisotropy or temperature differences in the Cosmic Microwave Background (CMB) radiation with high angular resolution and sensitivity, yielding unprecedented accuracy. To achieve this measurement, WMAP’s back-to-back Gregorian telescopes focus microwave radiation into 20 feed horns connected to 10 differential microwave radiometers. Proper alignment of the telescope reflectors, feed horns, and radiometers at flight temperatures was essential to the mission success. This paper will present the WMAP instrument metrology requirements and associated challenges, discuss the opto-mechanical tooling utilized to accomplish these objectives, and then give an overview of the metrology effort. The WMAP instrument integration effort included the following key metrology tasks: alignment and clocking of 20 microwave feed horns and mating microwave differencing assemblies within a focal plane assembly; alignment of a pair of primary and secondary reflectors composing back-to-back Gregorian telescopes; and the placement of the focal plane assembly and reflector system relative to each other, and as a unit on the spacecraft. WMAP environmental test metrology efforts included: reflector and truss thermal stability at 80 K; reflector and feed horn position verification at 90 K, and pre and post vibration and acoustic test reflector and feed horn position verification. The WMAP instrument integration and test objectives required the use of a photogrammetric camera, a laser tracker, a portable coordinate measuring machine (PCMM), and theodolites utilizing an electronic theodolite metrology system (ETMS) and autocollimation. The synergy of these metrology systems facilitated the successful characterization of the WMAP scientific instrument mechanical performance data at room temperature and flight temperatures, and correlation of the data to the analytical model. WMAP was launched on July 1, 2001, and flight data has confirmed the proper on-orbit instrument alignment was achieved.

JWST will have 5 to 10 times the collecting area of the Hubble Space Telescope, making it the largest optical system put into space by a large margin. Moreover, to keep the self-emission of the optics and detectors below the background, JWST will operate at cryogenic temperatures. In addition, JWST will operate at L2, where servicing is not a viable option; therefore, we must know that the JWST performs the way we expect it to before it launches. This requires establishing a high-confidence integration and verification process for a very large, cryogenic system while remaining affordable. This paper describes the verification process planned for JWST and the trades that led to this plan. The verification considers the all-important optical performance of the telescope itself, as well as the sunshield, the wavefront sensing and control system, the vibration isolation system, the spacecraft, and the end-to-end (photons in to data storage on the ground) performance verification. We discuss testing configurations, metrology methods, facilities, and the role of analytical modeling and testing at various stages of integration to ensure the performance is understood.

Kodak AMSD mirror processing was successfully completed, and the mirror was cryo tested at NASA. This paper reviews the entire AMSD program at Eastman Kodak Company from mirror blank production to mirror processing and metrology. To achieve the most information possible with respect to the flight configuration planned for JWST, the original Kodak AMSD test plan was modified. This change in plan is discussed and how it impacts the future path for AMSD. The AMSD Phase III program is also discussed and the status of that program is provided. In addition, this paper discusses performance of the mirror at cryo temperatures.

The 1.4-m semi-rigid, beryllium Advanced Mirror System Demonstrator (AMSD) mirror has been lightweighted by over 90% (achieving 10 kg/m² areal density) and optically ground and polished. The mounting structures have been completed and key attachments integrated prior to final polishing. The displacement actuators have been fabricated and tested at ambient and cryogenic temperatures. The integrated assembly represents an off-axis, aspheric, flight panel of a spaceborne mirror array whose radius of curvature (RoC) can be matched with its companion segments and whose position can be separately phased in a rigid body fashion. The results of the initial ambient testing and the cryogenic test set-up of the mirror assembly will be presented including mirror surface characterization and the correction afforded by radius of curvature actuation. Cryogenic testing at MSFC was completed in August 2003. The lightweighted, semi-rigid mirror architecture approach demonstrated here is a precursor to the mirror technology being applied to the James Webb Space Telescope (JWST).

This report describes the facility and experimental methods at the Goddard Space Flight Center Optics Branch for the measurement of the surface figure of cryogenically-cooled spherical mirrors using standard phase-shifting interferometry, with an uncertainty goal of 6 nm rms. The mirrors to be tested will be spheres with radius of curvature of 600 mm, and clear apertures of 120 - 150 mm. The optic surface will first be measured at room temperature using standard "absolute" techniques with an uncertainty of 2.6 nm rms; and then the change in surface figure error between room temperature and 20 K will be measured with an uncertainty goal of 5.4 nm rms. The mirror will be cooled within a cryostat, and its surface figure error measured through a fused-silica window. The facility and techniques are being developed to measure the cryogenic surface figure error of prototype lightweight mirrors being developed by the European Space Agency (ESA) and by US companies in SBIR's for NASA. This paper will present the measurement facility, methods and uncertainty analysis.

SLMS athermal technology has been demonstrated in the small 4-foot helium cryogenic test chamber located at the NASA/MSFC X-Ray Calibration Facility (XRCF). A SLMS Ultraviolet Demonstrator Mirror (UVDM) produced by Schafer under a NASA/MSFC Phase I SBIR was helium cryo tested both free standing and bonded to a Schafer designed prototype carbon fiber reinforced silicon carbide (Cesic) mount. Surface figure data was obtained with a test measurement system that featured an Instantaneous Phase Interferometer (IPI) by ADE Phase Shift. The test measurement system's minimum resolvable differential figure deformation and possible contributions from test chamber ambient to cryo window deformation are under investigation. The free standing results showed differential figure deformation of 10.4 nm rms from 295K to 27K and 3.9 nm rms after one cryo cycle. The surface figure of the UVDM degraded by lambda/70 rms HeNe once it was bonded to the prototype Cesic mount. The change was due to a small astigmatic aberration in the prototype Cesic mount due to lack of finish machining and not the bonding technique. This effect was seen in SLMS optical assembly results, which showed differential figure deformation of 46.5 nm rms from 294K to 27K, 42.9 nm rms from 294K to 77K, 28.0 nm rms from 294K to 193K and 6.2 nm rms after one cryo cycle.

We present a technique to characterize and quantitatively measure the vibrational mode shapes and amplitudes of mirrors concurrently with surface figure testing. The technique utilizes a fast interferometer that does not introduce any mass loading to the test structure. We present the fundamentals of the technique, discuss sevral modes of operation, such as resonant and transient response, and analyze the operational limits. The performance of the measurement system is characterized using a small ambient test mirror.

The University of Arizona has built a 2-m lightweight active mirror prototype for the next generation of space telescopes. This paper briefly reviews the mirror's opto-mechanical design, and it describes the three different metrology systems that were used to measure it during the actuation process. We also present a list of lessons learned while working on this project. We conclude by discussing one of the successful projects that has come out of this technology.

The wide variety of shapes, functions, and operational parameters of micro-electro-mechanical systems (MEMS) moving into production requires high flexibility for any commercial measurement instrumentation. Customers increasingly desire complete characterization of devices with both in-plane and out-of-plane motion over their full range of frequency, phase, and voltage inputs. Due to the tight tolerances on most MEMS devices, position, shape, and roughness must be measured to nanometer resolution. The parts themselves, however, can have steps up to several millimeters in height, while lateral features may range from a few microns to more than ten millimeters. Additionally, the devices must be characterized from their static state up to frequencies of one megahertz or more. These requirements pose large design challenges for both software and hardware for a system targeted to serve all of these measurement needs. While strobed systems have been used to exmaine moving devices for decades, these systems were generally quite specialized. Some could not measure static parts, while others have height or strict field-of-view limits. This paper describes the design of a general-purpose measurement system for dynamic MEMS components, and presents measurement results on a variety of MEMS devices with various features and modes of activation. Analyses including resonant frequency characterization, step response, and dynamic deformation will be presented on multiple devices.

Micro-optic components and subsystems are becoming increasingly important in optical sensors, communications, data storage, and many other diverse applications. In order to adequately predict the performance of the final system, it is important to understand how the optical elements affect the wavefront as it is transmitted through the system. The wavefront can be measured using interferometric means, however, both random and systematic errors contribute to the uncertainty of the measurement. If an artifact is used to calibrate the system it must itself be traceable to some external standard. Self-calibration techniques exploit symmetries of the measurement to separate the systematic errors of the instrument from the errors in the test piece. If the transmitted wavefront of a ball lens is measured in a number of random orientations and the measurements are averaged, the only remaining deviations from a perfect wavefront will be due to spherical aberration contributions from the ball lens and the systematic errors of the interferometer. If the radius, aperture, and focal length of the ball lens are known, the spherical aberration contributions can be calculated and subtracted, leaving only the systematic errors of the interferometer. This paper develops the theory behind the technique and describes the calibration of a micro-interferometer used to measure the transmitted wavefront error of micro-refractive lenses.

Micro-optics are essential components for building compact optoelectronic and micro-electro-optical mechanical systems and micro-refractive lenses are an important example. Refractive lenses are continuous relief structures and details of their dimensional shape, refractive index and homogeneity strongly influence performance. Some dimensional and transmitted light properties of the refractive components can be measured with scanning white light interferometers (SWLI), profilometers, and phase-shifting micro-interferometers, however limitations exist with each method. Micro-interferometry is the most promising and can be used to measure radius of curvature, focal length, dimensional surface errors, and transmitted wavefront. However, methods have not been optimized to achieve low uncertainties. Systematic biases can be comparable to figure errors on the part, therefore a rigorous calibration method is needed. Current practice involves measuring a very high quality part and measured errors are equated to instrument biases. It is often difficult, however, to obtain such a part. The alternative is to use a self-calibration test. As an alternative, the random ball test can be applied to micro-interferometers and SWLIs for self-calibration. This paper details the implementation of this test for both types of instruments and describes the method of estimating the calibration uncertainty.

An interferometrical measurement method is presented for determining the quality of cylindrical micro lenses with a numerical aperture of up to 0.8 in transmitted light. In order to maximize the achievable accuracy, a null test configuration was chosen. The reference cylindrical waves are shaped by computer generated diffractive optical elements (DOEs), which are made by optical or e-beam lithography. The resulting wave front is analyzed by a fiber optic phase-shifting Mach-Zehnder-interferometer or a Shack-Hartmann wave front sensor. Besides the general setup, which is working in the near infrared (NIR), special aspects will be presented concerning the elimination of misalignment aberrations, the complete filtering of parasitic diffraction orders and the generation of an anamorphic optical transformation for increasing the lateral resolution perpendicular to the cylindrical axis. By means of experimental results the possibilities and accuracy of this technique are discussed.

Radius of curvature is a critical parameter to measure in the manufacturing of micro-refractive elements. It defines the power of the surface and provides important information about the stability and uniformity of the manufacturing process. The radius of curvature of an optical surface can be measured using an interferometer and radius slide where the distance is measured as the surface is moved between the confocal and cat’s eye positions. However, the radius of curvature for micro-refractive elements can be on the order of a few hundred microns and the uncertainty in the measurement due to stage error motions can become a significant portion of the tolerance. Typically the radius slide is calibrated using an artifact, but the radius of the artifact must be traceable to the base unit of length and the calibration is subject to misalignment errors. Alternatively, the stage error motions can be measured with standard machine tool metrology techniques and used to correct the errors in the radius of curvature measurement. This paper details the implementation of a directly traceable radius of curvature measurement on a micro-interferometer, including alignment procedures, measurement of stage error motions, displacement gauge calibration, and data analysis strategies.

DWDM (dense wavelength division multiplexing) telecommunication applications depend on precise and dependable tuning and spacing of multiple optical frequencies, a task usually performed by etalons. The manufacture and quality assurance of these etalons requires an accurate, stable and deterministic measurement system. At VLOC, a JDSU swept-wavelength laser calibrated with an acetylene absorption cell was merely the starting point. By massive computerized data collection, curve-fitting, unique algorithms, and statistical methods, all performed within a custom LabView program, we were able to bootstrap the information from this system and achieve FSR measurement accuracy and stability far in excess of typical methods. In this paper we present the logical development of the technique, statistical modeling, and typical results. To date the system has been used for solid and air-gap etalons, both coated and uncoated, from 16 to 400 GHz FSR.

Cemented doublets and triplets, which are the principle parts in high quality, high numerical aperture (NA) objectives, can not be used for objectives working at wavelengths of 248 nm and shorter, because the optical cement can not withstand the high photon energies. We will show that high NA deep UV objectives can be designed and built successfully with the help of air spaced doublets. Assuring Strehl ratios above 95% enforces very tight tolerances. For example the distance error of the lens vertex to its mount has to be <1 μm. This calls for a new manufacturing precision never realized before in series production. We show how a white light Mirau interferometer can be used to measure lens vertex positions with an accuracy of ±200 nm. We also demonstrate how the fine-tuning process can be optimized by using a "simulated star test," where the point-spread function is calculated in real time with a FFT-algorithm from the optical path difference data, acquired by a Twyman-Green interferometer.

During the last years compact CMOS imaging cameras have grown into high volume applications such as mobile phones, PDAs, etc. In order to insure a constant quality of the lenses of the cameras, MTF is used as a figure of merit. MTF is a polychromatic, objective test for imaging lens quality including diffraction effects, system aberrations and surface defects as well. The draw back of MTF testing is that the proper measurement of the lens MTF is quite cumbersome and time consuming. In the current investigation we designed, produced and tested a new semi-automated MTF set up that is able to measure the polychromatic lens system MTF at 6 or more field points at best focus in less than 6 seconds. The computed MTF is a real diffraction MTF derived from a line spread function (not merely a contrast measurement). This enables lens manufacturers to perform 100% MTF testing even in high volume applications. Using statistic tools to analyze the data also gives possibility to find even small systematic errors in the production like shift or tilt of lenses and lens elements. Using this as feedback the quality of the product can be increased. The system is very compact and can be put easily in an assembly line. Besides design and test of the MTF set up correlation experiments between several testers have been carried out. A correlation of better than 6% points for all tested systems at all fields has been achieved.

Testing in a non-null manner causes the test and reference rays in the interferometer to follow different optical paths through the system. The retrace errors generated by this difference are test dependent and must be calibrated independently for each test piece. Optical design software can be used to perform reverse optimization of the interferometer and data. An iterative reverse optimization process has been developed which eliminates weighting sensitivity and improves optimization efficiency. However, implementation of reverse optimization generates constraints on the interferometer design. These include constraints on lens parameters, system apertures, and component verification considerations. A Mach-Zehnder interferometer has been built for non-null transmitted aspheric wavefront testing. The large aspheric departures and steep wavefront slopes are detected and reconstructed using Sub-Nyquist interferometry (SNI). Experiments on several test parts were performed to verify the iterative reverse optimization process and extend the use of SNI to non-rotationally symmetric aspheric wavefronts. Wavefront departures up to 200λ were characterized to λ/6 PV and λ/47 rms. The reverse optimization process was shown to remove up to 25λ of induced aberration from an aspheric measurement. The results indicate potential for application of the iterative method and its associated design constraints to routine aspheric testing.

Recently the lens fabrication technique is developed so fast that an aspherical surface is often used to achieve better imaging performance or reduce number of elements. Especially the popularity of micro-optics and miniature imaging system makes the use of aspherical optics very common. However the metrology of aspherical micro-optics has been disregarded and outpaced by the fabrication technique. It results in the lack of ignorance of metrology for aspherical micro-optics. This paper suggests the simple and cost-effective methodology for aspherical micro-optics by using computer generated hologram (CGH). Although the CGH technique is well-known and well-established technique for relatively larger aspherical optics, it is seldom used for micro-optics testing where there is higher demand of aspherical optics testing. By reporting the success of aspherical micro-optics testing in this paper, we confirm that CGH technique will play an important role to answer new demand of metrology.

The Shack-Hartmann (S-H) method is a good candidate for general aspheric metrology because the lenslet array can be designed to accommodate the dynamic range associated with wildly aspheric wavefronts. However, when the S-H method is used in this fashion several issues must be taken into consideration. First, while the sensitivity and dynamic range of the instrument can be increased by allowing the spots to shift several lenslet sub-apertures, real lenslets are not thin lenses with zero aperture so the spots will not shift in exact proportion to the average phase gradient across the lenslet as is commonly expected. Second, if the wavefront is sufficiently aspheric, any relay optics will induce additional aberrations, which can be accounted for with proper calibration and reverse raytracing. Another limitation of the S-H method is that spots cannot overlap or cross. While this is a limitation on the divergence of the phase distribution or wavefront curvature the problem can be avoided if we guarantee that the beam has no caustic between the lenslet array and detector. Finally, the single biggest problem in aspheric metrology is losing the light or vignetting. One general way to address this problem is to image the part onto the lenslet array with a large numerical aperture. In this way, rays leaving the part can have some range of angles that are guaranteed to make it through the system. This presentation will discuss these issues and methods for overcoming them. Experimental results will also be presented to demonstrate the effects.

Rapid growth in the contact lens industry towards higher levels of customization has precipitated the need for advances in the metrology techniques and instrumentation used to evaluate soft contact lenses. By measuring the transmitted wavefront, the information needed to evaluate a wide range of lens types (spherical, toric, bifocal) is obtained. A Mach-Zehnder interferometer is used with the lenses tested in saline solution. The lenses must be tested in saline solution to prevent dehydration of the lens, which results in an index change. The lenses are mounted in a cuvette, or water cell, that circulates fresh saline. Calibration of the instrument is complicated by the aspheric wavefronts produced by the lenses and the inherent aberrations picked up by the wavefront as it is imaged from immediately behind the lens to the detector. Simply removing a baseline, no test optic measurement from the measured wavefront does not satisfactorily remove the induced aberrations. Instead, removal of the induced aberrations is achieved by reverse raytracing. In reverse raytracing, the wavefront at the detector is traced back through the system to immediately behind the lens. The use of raytracing code enables theoretical wavefronts to be generated and expected-to-calculated performance evaluations to be made at the transmitted wavefront level.

A method for measuring symmetric aberrations in large departure aspheric surfaces to nearly single digit nanometer precision is demonstrated. Interferometry can accurately measure plano, spherical and small departure aspheric surfaces. However, null correction is normally required for accurate interferometric measurement of large departure aspheres. When using conventional null lenses, asymmetric aberrations are easily measured by simply rotating the surface under test to a finite number of positions and comparing them to one another. The rotationally symmetric errors are more difficult to know with certainty due to possible systematic rotationally symmetric errors with the null lens itself. The proposed system can measure aspheres on planar to f/6.0 spherical surfaces with a maximum sag of 1 mm and from 800 mm to 25 mm spherical surfaces down to f/0.55. A non-contact interferometric probe is used to measure the surface profile with the optic mounted on either a linear or rotary air bearing, depending on the base radius of curvature of the optic. Measurement results are shown for several aspheres and compared with interferometer measurements.

Optical profilers that employ white-light interferometry (WLI) techniques are widely used in industry and research to map surface structures with precise sub-nanometer resolution. The accuracy, repeatability and consistency of these instruments depend mainly on the proper calibration of two parameters: the mean wavelength and the scanner speed. Equally important in industrial applications is high throughput of measuring devices; high throughput can be achieved by increasing the speed of the measurement, which in turn reduces the sampling rate of the interference signal. Again, exact calibration of the system is the key to obtaining accurate measurements. Our solution for calibrating the system involves inserting into the optical profiler a second, laser-based, reference signal interferometer that creates a primary length standard for calibration. This innovation allows for substantially improved performance and repeatability at different measurement speeds up to 100 microns per second and over an 8 millimeter scanning range.

We propose an effective algorithm for surface profiling by white-light interferometry based on the so-called partial projection filter, which is a signal estimation technique from a finite number of noisy sampled data. The present authors' group has proposed a fast surface profiling algorithm called the SEST algorithm, in which the world's widest sampling interval of 1.425μm is used. The SEST algorithm, however, has the following problem. That is, when we reduce the sampling interval in order to improve the measurement accuracy, the performance does not increase. In order to solve this problem, the new algorithm has been proposed. That is, when the sampling interval of 1.425μm is used, the new algorithm achieves the same performance as the SEST algorithm. When a narrower sampling interval than 1.425μm is used, the new algorithm improves the accuracy. By computer simulations, the effectiveness of the new algorithm is confirmed.

As requirements for surface slope errors in synchrotron radiation beam line optics approach the 100 nrad level on a routine basis, it becomes necessary to improve the performance of metrology instrumentation to provide reliable, repeatable, and accurate measurements at this level. We have identified a number of internal error sources in the Long Trace Profiler (LTP) that affect measurement quality at this level. The LTP is sensitive to phase shifts produced within the millimeter diameter of the pencil beam probe by optical path irregularities with scale lengths on the order of a millimeter. We examine the effects of mirror surface "macroroughness" and internal glass homogeneity on the accuracy of the LTP through experiment and theoretical modeling. By careful characterization and selection of the quality of the optical components that comprise the LTP optical system, it is possible to reduce the systematic errors in the measurement to well below the 1 microradian level.

In this paper, the multi-aperture overlap-scanning technique (MAOST) and its recent developments are presented. In the first instance, MAOST is used in interferometry, and the principle of MAOST for interferometry is that, a tested large-scale plane is covered by an array of interferometric subapertures, and the relationship between each couple of adjacent subapertures is determined from their overlapping areas by a least squares method, and then the profile of tested plane is obtained by connecting all the subapertures together. Recently, to meet the requirements of advanced manufacturing, the idea of MAOST has been extended to precision three-dimensional (3-D) measurement. In practice, a whole-body 3-D shape is acquired by two steps: first measuring the 3-D shape from different views and afterwards connecting all the views together. In order to accurately determine the position and orientation of every single-view in a common coordinate system, an iterative algorithm based on MAOST concept is utilized.

Manufacturers of optical glass strive to make a product that is homogeneous, isotropic, and free of any bubbles or mechanical strain. Glass used in forming images is very good, but the process of mixing the constituent materials, and melting them into a glass is limited. As uniform as the mixtures are, they are not perfect, and the effects can be seen anytime light must propagate through several centimeters of glass. One method for measuring the three dimensional inhomogeneities in a piece of glass will be shown. Interferometry and computed tomography will be used to map the bulk refractive index variations. Having three dimensional information on the refractive index is the first step in compensating for errors in an imaging system.

Wavelength-scanning interferometry allows the simultaneous measurement of the surface profile and the optical thickness variation of a parallel plate. Previously we have derived two error-compensating algorithms for the detection of the fundamental and third harmonic frequencies. This requires a certain fixed ratio of the interferometer's air gap width to the optical thickness of the parallel plate. As the test plate becomes thinner, so does the air gap of the interferometer, and the wavelength-tuning range eventually becomes insufficient to give the necessary phase shift. By swapping the detection frequencies of the two algorithms, the phase-shift step can be augmented threefold compared with the previous interval. The resultant scheme allows a three-times larger air gap and hence requires only one third of the wavelength-tuning range compared with the previous scheme. Measurements of a BK7 plate of 1 mm thickness and a ZnSe plate of 5 mm thickness in a Fizeau interferometer showed residual errors caused by nonlinear wavelength-scanning and higher order multiple-reflections.

Many approaches to compute the wavefront of interferometer have been devised, for example least squares method, Gram-Schmidt method, covariance matrix method and SVD method, but one of the most interesting is based on the Zernike Polynomials. Zernike polynomials are ideal for fitting the measured data points in a wavefront to a two-dimensional polynomial, due to their orthogonal properties. The key problem of wavefront fitting is how to express exactly the whole wavefront. In established algorithms, the fixed mode number of Zernike polynomials is used, for example most analyzing software using 36 Zernike polynomials (i.e., Metropro of Zygo). When analyzing high spatial frequency aberrations, the analyzed result is not accurate. We develop a method of wavefront fitting with regression analysis. Regression analysis is the most widely used technique in statistics, and it is a statistical technique for investigating and modeling the relationship between variables. With stepwise regression we obtain the optimum combination of mode, and the wavefront can be exactly expressed.

In this paper, we analyze the phase-shifting algorithm by utilizing Fourier transformation theory. In fact, the phase-shifting algorithm is corresponding to a discrete Fourier transformation (DFT), the image capturing operation is a temporal sampling procedure, and the purpose of phase-shifting technique is to retrieve the phase of one frequency component. According to the sampling theory, if the number of phase steps is too less that means a too low sampling frequency is adopted, the frequency of interest will be mixed with high order spectra. By mathematical analysis, the relationship between the number of phase steps and the effect of harmonics is deduced, and the criterion of selecting phase step number is discussed. The applications of the Fourier analysis in digital fringe projection profilometry are described.

We have implemented a variation of the classical Hartmann test on a commercial lens bench. We use a single motorized aperture for scanning in X,Y, an image analysis microscope with CCD detector, and image processing software. In a short time, it is possible to measure and plot the wavefront tilt at hundreds of points across the entrance pupil. The technique combines both high sensitivity and large dynamic range. For example, is possible to measure wavefront tilt to 1/200 wave across a 1.5 mm sampling aperture. The high dynamic range allows useful measurement of poorly molded plastic lenses whose surface figure would not yield useable fringes on an interferometer.

An on-machine measuring system based on the use of an LTP optical head was developed to accurately measure the slope error and profile error of long parts just after machining. Cylindrical surfaces can be measured completely by steering the beam up the sides of the cylinder with a rotatable mirror. To increase the reliability to measure the cylindrical surfaces, the optical system of the LTP head was improved. A personal computer collects all the data and controls the machine positioning and the beam steering mirror automatically.

In optical three-dimensional measurement, fringe projection technique has found more and more applications. However, in 3D measurement of complex objects, due to the inherent limitation of triangulation, occultation is unavoidable. Meanwhile, the surface of the measured object usually contains discontinuities or the object profile is often sharply steep. Another problem is that for the measurement of a surface with complex reflectivity or quasi-specular, the resulting phase values are unreliable. Therefore, there must be some invalid areas caused by shadow, phase errors or discontinuities, etc. in just a single-view. For compensating the lacked 3-D coordinates of the points in the areas, the multi-frequency fringe projection method is used and temporal phase unwrapping is applied. Invalid areas are marked and further cancelled according to the modulation and phase fitting reliability. To obtain the whole 3D world coordinates of the measured object, a novel connection method based on the principle of the virtual cylinder is presented to accurately integrate the 3D coordinates of every single-view into a global coordinate system. The connection method derives from a technique named Multi-view (aperture) Overlap-scanning Technique (MAOST) based on overlapping areas. The measurement results of an automobile headlamp reflector are experimentally presented to demonstrate the validity.

A simple phase shifting (PS) technique without moving element in lateral shearing (LS) interferometer is presented. This method uses Murty’s simple LS interferometer with a wedge plate and adds only two identical transmission gratings. The two gratings can make three (or odd number of) equally separated identical test wavefronts. The wedge plate changes the optical path difference between the original wavefront and the sheared wavefront along the wedge direction. So three (or odd number of) interferograms having different phase shift quantity can be obtained simultaneously and 3-step PS interferometry algorithm can be applied.