This PDF file contains the front matter associated with SPIE Proceedings Volume 9633 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

With CO₂-laser radiation glass material can be melted and ablated. These processes are used to reduce the surface roughness of optics by melting (laser polishing) as well as to reduce form errors by ablation (high precision laser ablation). The manufacturing time in particular for polishing and form correction of nonspherical optics can be reduced significantly. Current results of laser polishing and high precision laser ablation are presented. With laser polishing, the surface roughness of fused silica, borosilicate glass (BK7) and flint glass (S-TIH6) can be reduced significantly. But, the achieved waviness is not yet sufficient for imaging optics. Hence, high precision laser ablation is used to ablate material locally in a vertical dimension down to 5 nm.

Lower cost additive manufacturing (AM) machines which have emerged in recent years are capable of producing tools, jigs, and fixtures that are useful in optical fabrication. In particular, AM tooling has been shown to be useful in lapping glass workpieces. Various AM machines are distinguished by the processes, materials, build times, and build resolution they provide. This research investigates the impact of varied build resolution (specifically layer resolution) on the lapping performance of tools built using the stereolithographic assembly (SLA) process in 50 μm and 100 μm layer thicknesses with a methacrylate photopolymer resin on a high resolution desktop printer. As with previous work, the lapping tools were shown to remove workpiece material during the lapping process, but the tools themselves also experienced significant wear on the order of 2-3 times the mass loss of the glass workpieces. The tool wear rates for the 100 μm and 50 μm layer tools were comparable, but the 50 μm layer tool was 74% more effective at removing material from the glass workpiece, which is attributed to some abrasive particles being trapped in the coarser surface of the 100 um layer tooling and not being available to interact with the glass workpiece. Considering the tool wear, these additively manufactured tools are most appropriate for prototype tooling where the low cost (<$45) and quick turnaround make them attractive when compared to a machined tool.

Cerium oxide, because of its commonality to the optical workshop, is often used as the go-to abrasive for polishing many different substrates. For silica containing substrates, cerium oxide is an excellent abrasive choice because it allows for both chemical and mechanical polishing. However, plastic lenses do not contain silica and thereby cannot undergo the same chemical reaction with cerium oxide. These substrates are also very vulnerable to sleeks and scratches, and the tabular cerium oxide can impart defects into the surface resulting in scratch-dig failures and higher than expected surface roughness values. With the recent market push for plastic optical components, selection of an appropriate polishing slurry is critical to maintaining a competitive edge in the market and a profitable business.

In this paper, the authors will show how using an aluminum oxide can improve performance on thermoset and thermoplastic resins like polycarbonate, Zeonex^® and Acrylic^a. The shape of the aluminum oxide allows for reduced defectivity while the high hardness of the abrasive allows for a removal rate tunable to the substrate hardness.

In Automotive applications, sintered Silicon Carbide has been used in applications such as seal pump faces. The surface of sintered SiC, when lapped or polished for sealing to another surface, must be free of blemishes and mechanical defects. Lapping and polishing processes therefore must be well defined and controlled assuring minimal variation and production scrap. In this study, we related the characteristics of different diamond powders (particle size distribution, particle shape and surface) to their performance in lapping of sintered silicon carbide material, expressed as removal rate and surface finish.

We present a modified version of zirconia-coated carbonyl-iron (CI) particles that were invented at the University of Rochester in 2008. The amount of zirconia on the coating is increased to further protect the iron particles from corrosion when introduced to an acidic environment. Five low-pH, magnetorheological (MR) fluids were made with five acids: acetic, hydrochloric, nitric, phosphoric, and hydrofluoric. All fluids were based on the modified zirconia-coated CI particles. Off-line viscosity and pH stability were measured for all acidic MR fluids to determine the ideal fluid composition for acidic MR finishing of chemical-vapor–deposited (CVD) zinc sulfide (ZnS) and other infrared (IR) optical materials, such as hot-isostatic-pressed (HIP) ZnS, CVD zinc selenide (ZnSe), and magnesium fluoride (MgF₂). Results show significant reduction in surface artifacts (millimeter-size, pebble-like structures on the finished surface) for several standard-grade CVD ZnS substrates and good surface roughness for the non-CVD MgF₂ substrate when MR finished with our advanced acidic MR fluid.

We have selected three colloidal silica slurries and compared their ability for fused silica finishing, by varying the load and slurry concentration. We found that the process parameters can affect differently the finishing efficiency, roughness and surface defects density, depending on the slurry considered.

Fiber arrays are used to connect arrayed waveguide chips. The end-faces of fiber array components are multi-materials non-uniform surfaces. Their low polishing quality has become a bottleneck that restricts coupling performance of integrated photo-electronic devices. The chemical mechanical polishing (CMP) is normally used to improve the polishing quality of the end-faces of fiber array components. It is very important to optimize process parameters by researching the mechanical behavior of nanoparticles and material microstructure evolution on the CMP interfaces. Based on the elastic and hyper-elastic contact of the soft polishing particle with quartz glass and polishing pad, the material removal mechanism at molecular scale of polishing process for quartz glass using soft polishing particles is investigated, and the material removal rate model is also derived by using Arrhenius theory and molecule vibration theory. Theoretical and experimental results show that the material is mainly removed by the interfacial tribo-chemical effect between polishing particle and quartz glass during CMP process. The depth of a single particle embedding into the quartz glass is at molecular scale, and the superficial molecules of quartz glass are removed by chemical reactions because of enough energy obtained. The material removal rate of quartz glass during CMP process is determined by the polishing pressure, the chemical reagents and its concentration, and the relative movement speed between the quartz glass workpiece and the polishing pad.

Scratches at the surface of fused silica optics can be detrimental for the performance of optical systems because they initiate damage on the optic but also they perturb the amplitude or phase of the transmitted laser light. Removing scratches by conventional polishing techniques can be time consuming as it is an iterative and long process, especially when hours of polishing time are required to obtain very high surface accuracy. So we have investigated ways to remove them with local laser processing. The silica is then heated at temperature higher than the softening point to heal the cracks.

We report a correlation between the scattering value “Aq” and the ISO standardized roughness parameter Rq. The Aq value is a measure for surface smoothness, and can easily be determined from an optical scattering measurement. The correlation equation extrapolates the Aq value from a narrow measurement range of ±16° from specular to a broader range of ±80°, corresponding to spatial surface wavelengths of 0.8 μm to 25 μm, and converts the Aq value to the Rq value for the surface.

Furthermore, we present an investigation of the changes in scattering intensities, when a surface is covered with a thin liquid film. It is shown that the changes in the angular scattering intensities can be compensated for the liquid film, using empirically determined relations. This allows a restoration of the “true” scattering intensities which would be measured from a corresponding clean surface. The compensated scattering intensities provide Aq values within 5.7 % ± 6.1 % compared to the measurements on clean surfaces.

Improving predictability in optical fabrication can go a long way towards increasing profit margins and maintaining a competitive edge in an economic environment where pressure is mounting for optical manufacturers to cut costs. A major source of hidden cost is rework – the share of production that does not meet specification in the first pass through the polishing equipment. Rework substantially adds to the part’s processing and labor costs as well as bottlenecks in production lines and frustration for managers, operators and customers. The polishing process consists of several interacting variables including: glass type, polishing pads, machine type, RPM, downforce, slurry type, baume level and even the operators themselves. Adjusting the process to get every variable under control while operating in a robust space can not only provide a deterministic polishing process which improves profitability but also produces a higher quality optic.

Sapphire presents many challenges to optical manufacturers due to its high hardness and anisotropic properties. Long lead times and high prices are the typical result of such challenges. The cost of even a simple 'grind and shine' process can be prohibitive. The high precision surfaces required by optical sensor applications further exacerbate the challenge of processing sapphire thereby increasing cost further. Optimax has demonstrated a production process for such windows that delivers over 50% time reduction as compared to traditional manufacturing processes for sapphire, while producing windows with less than 1/5 wave rms figure error.

Optimax's sapphire production process achieves significant improvement in cost by implementation of a controlled grinding process to present the best possible surface to the polishing equipment. Following the grinding process is a polishing process taking advantage of chemical interactions between slurry and substrate to deliver excellent removal rates and surface finish. Through experiments, the mechanics of the polishing process were also optimized to produce excellent optical figure. In addition to reducing the cost of producing large sapphire sensor windows, the grinding and polishing technology Optimax has developed aids in producing spherical sapphire components to better figure quality.

In addition to reducing the cost of producing large sapphire sensor windows, the grinding and polishing technology Optimax has developed aids in producing spherical sapphire components to better figure quality. Through specially developed polishing slurries, the peak-to-valley figure error of spherical sapphire parts is reduced by over 80%.

Precision optical elements are used in a wide range of technical instrumentations. Many optical systems e.g. semiconductor inspection modules, laser heads for laser material processing or high end movie cameras, contain precision optics even aspherical or freeform surfaces. Critical parameters for such systems are wavefront error, image field curvature or scattered light. Following these demands the lens parameters are also critical concerning power and RMSi of the surface form error and micro roughness. How can we reach these requirements? The emphasis of this discussion is set on the application of subaperture correction technologies in the fabrication of high-end aspheres and free-forms. The presentation focuses on the technology chain necessary for the production of high-precision aspherical optical components and the characterization of the applied subaperture finishing tools MRF (magneto-rheological finishing) and IBF (ion beam figuring). These technologies open up the possibility of improving the performance of optical systems.

Surfaces are commonly specified with peak to valley (PV) and root-mean-square (rms) requirements for surface form and roughness, describing surface quality with a few simple numbers. These specs ignore lateral feature sizes between form and roughness (so-called mid-spatial frequencies, or MSFs), however, making them inadequate for many modern optics fabricated with advanced technologies. Specifications sensitive to the lateral feature size, such as such as slope or power-spectral density (PSD), are increasingly employed to fill this void. Having a detailed view of the surface error as a function of lateral feature size can drive fabrication decisions. For example, a large aperture tool tends to correct small features well but performs less well on large features; while subaperture tools tend to do the opposite.

Therefore after each fabrication step we want to know how the surface features at different lateral sizes evolved, so that we can optimize the choice of the next fabrication step. A spec like PSD often doesn’t inform the fabricator whether it’s failing because of a localized error (such as edge roll), continuous texture, or an artifact of metrology or computation. So while it may indicate the need for additional fabrication steps, it is not ideal for guiding specifically which fabrication step ought to be undertaken next. We have developed analyses to help determine what surface characteristics are failing spec, and thus optimize the next fabrication step. Finally, we demonstrate an example of how we have applied these techniques to fabricate parts with demanding slope and MSF specifications.

An increasing number of technologies require ultra-low roughness (ULR) surfaces. Magnetorheological Finishing (MRF) is one of the options for meeting the roughness specifications for high-energy laser, EUV and X-ray applications. A novel MRF fluid, called C30, has been developed to finish surfaces to ULR. This novel MRF fluid is able to achieve <1.5Å RMS roughness on fused silica and other materials, but has a lower material removal rate with respect to other MRF fluids. As a result of these properties, C30 can also be used for applications in addition to finishing ULR surfaces. These applications include fine figure correction, figure correcting extremely soft materials and removing cosmetic defects. The effectiveness of these new applications is explored through experimental data. The low removal rate of C30 gives MRF the capability to fine figure correct low amplitude errors that are usually difficult to correct with higher removal rate fluids. The ability to figure correct extremely soft materials opens up MRF to a new realm of materials that are difficult to polish. C30 also offers the ability to remove cosmetic defects that often lead to failure during visual quality inspections. These new applications for C30 expand the niche in which MRF is typically used for.

The increased use of aspheres in today’s optical systems has led to specialized manufacturing equipment and processes that are needed to meet component specifications. Due to their sub-aperture nature, each stage of these processes can leave behind a signature that could adversely affect the asphere's overall performance. Utilizing a variety of grinding and polishing techniques can help minimize residual artifacts that are left in an asphere.

OptiPro has performed extensive process development work to understand how to grind and polish aspheres at production speeds with minimized process signatures. For example, the amount of stock removed from a substrate using a sub aperture polishing process can increase the amount of mid-spacial frequencies that can be detected. Through precise grind control, sub aperture, and mid-aperture polishing process research, OptiPro developed a detailed knowledge of asphere process control. One of the outcomes of this work has led OptiPro to develop an asphere polishing head for their 160A polishing platform which allows more process flexibility and control.

Aspheric lenses are ground in a single point cutting mode. Subsequently different iterative polishing methods are applied followed by aberration measurements on external metrology instruments. For an economical production, metrology and correction steps need to be reduced. More deterministic grinding and polishing is mandatory.

Single point grinding is a path-controlled process. The quality of a ground asphere is mainly influenced by the accuracy of the machine. Machine improvements must focus on path accuracy and thermal expansion. Optimized design, materials and thermal management reduce thermal expansion. The path accuracy can be improved using ISO 230-2 standardized measurements. Repeated interferometric measurements over the total travel of all CNC axes in both directions are recorded. Position deviations evaluated in correction tables improve the path accuracy and that of the ground surface.

Aspheric polishing using a sub-aperture flexible polishing tool is a dwell time controlled process. For plano and spherical polishing the amount of material removal during polishing is proportional to pressure, relative velocity and time (Preston). For the use of flexible tools on aspheres or freeform surfaces additional non-linear components are necessary. Satisloh ADAPT calculates a predicted removal function from lens geometry, tool geometry and process parameters with FEM. Additionally the tool´s local removal characteristics is determined in a simple test. By oscillating the tool on a plano or spherical sample of the same lens material, a trench is created. Its 3-D profile is measured to calibrate the removal simulation. Remaining aberrations of the desired lens shape can be predicted, reducing iteration and metrology steps.

The centering of an optical lens is the grinding of its edge profile or contour in relationship to its optical axis. This is required to ensure that the lens vertex and radial centers are accurately positioned within an optical system. Centering influences the imaging performance and contrast of an optical system. Historically, lens centering has been a purely manual process. Along its 62 years of assembling centering machines, Satisloh introduced several technological milestones to improve the accuracy and quality of this process. During this time more than 2.500 centering machines were assembled. The development went from bell clamping and diamond grinding to Laser alignment, exchange chuckor –spindle systems, to multi axis CNC machines with integrated metrology and automatic loading systems. With the new centering machine C300, several improvements for the clamping and grinding process were introduced. These improvements include a user friendly software to support the operator, a coolant manifold and “force grinding” technology to ensure excellent grinding quality and process stability. They also include an air bearing directly driven centering spindle to provide a large working range of lenses made of all optical materials and diameters from below 10 mm to 300 mm. The clamping force can be programmed between 7 N and 1200 N to safely center lenses made of delicate materials. The smaller C50 centering machine for lenses below 50 mm diameter is available with an optional CNC loading system for automated production.

As optical geometries become more precise and complex and a wider range of materials are used, the processes used for manufacturing become more critical. As the preparatory stage for polishing, this is especially true for grinding. Slow processing speeds, accelerated tool wear, and poor surface quality are often detriments in manufacturing glass and hard ceramics. The quality of the ground surface greatly influences the polishing process and the resulting finished product.

Through extensive research and development, OptiPro Systems has introduced an ultrasonic assisted grinding technology, OptiSonic, which has numerous advantages over traditional grinding processes. OptiSonic utilizes a custom tool holder designed to produce oscillations in line with the rotating spindle. A newly developed software package called IntelliSonic is integral to this platform. IntelliSonic automatically characterizes the tool and continuously optimizes the output frequency for optimal cutting while in contact with the part. This helps maintain a highly consistent process under changing load conditions for a more accurate surface. Utilizing a wide variety of instruments, test have proven to show a reduction in tool wear and increase in surface quality while allowing processing speeds to be increased.

OptiSonic has proven to be an enabling technology to overcome the difficulties seen in grinding of glass and hard optical ceramics. OptiSonic has demonstrated numerous advantages over the standard CNC grinding process. Advantages are evident in reduced tool wear, better surface quality, and reduced cycle times due to increased feed rates. These benefits can be seen over numerous applications within the precision optics industry.

Technologies including magnetorheological finishing and CNC polishing are commonly used to finish optical elements, but these methods are often expensive, generate waste through the use of fluids or abrasives, and may not be suited for specific freeform substrates due to the size and shape of finishing tools. Pulsed laser polishing has been demonstrated as a technique capable of achieving nanoscale roughness while offering waste-free fabrication, material-specific processing through direct tuning of laser radiation, and access to freeform shapes using refined beam delivery and focusing techniques. Nanosecond and microsecond pulse duration radiation has been used to perform successful melting-based polishing of a variety of different materials, but this approach leads to extensive heat accumulation resulting in subsurface damage. We have experimentally investigated the ability of femtosecond laser radiation to ablate silicon carbide and silicon. By substituting ultrafast laser radiation, polishing can be performed by direct evaporation of unwanted surface asperities with minimal heating and melting, potentially offering damage-free finishing of materials. Under unoptimized laser processing conditions, thermal effects can occur leading to material oxidation. To investigate these thermal effects, simulation of the heat accumulation mechanism in ultrafast laser ablation was performed. Simulations have been extended to investigate the optimum scanning speed and pulse energy required for processing various substrates. Modeling methodologies and simulation results will be presented.

We propose a new method for polishing the corners of optical surfaces that uses a plate spring as a polishing tool. In this method, a polishing pad is fixed to the tip of a plate spring, which moves back and forth on a workpiece surface. During the polishing, the plate spring is bent while maintaining a constant amount of deflection to generate a stable polishing load. The edge of the plate spring enables the polishing of the corners of the workpiece. We have developed a polishing machine with a plate spring, and we performed polishing experiments on silicon plates to investigate the fundamental characteristics of our proposed method. It was found that the roughness of workpiece surfaces decreases with the progress of polishing and that the areas are polished almost uniformly, demonstrating the effectiveness of our polishing method.

Fast, robust, nondestructive 3D imaging is needed for characterization of microscopic structures in industrial and clinical applications. A custom micro-electromechanical system (MEMS)-based 2D scanner system was developed to achieve 55 kHz A-scan acquisition in a Gabor-domain optical coherence microscopy (GD-OCM) instrument with a novel multilevel GPU architecture for high-speed imaging. GD-OCM yields high-definition volumetric imaging with dynamic depth of focusing through a bio-inspired liquid lens-based microscope design, which has no moving parts and is suitable for use in a manufacturing setting or in a medical environment. A dual-axis MEMS mirror was chosen to replace two single-axis galvanometer mirrors; as a result, the astigmatism caused by the mismatch between the optical pupil and the scanning location was eliminated and a 12x reduction in volume of the scanning system was achieved. Imaging at an invariant resolution of 2 μm was demonstrated throughout a volume of 1 × 1 × 0.6 mm³, acquired in less than 2 minutes. The MEMS-based scanner resulted in improved image quality, increased robustness and lighter weight of the system – all factors that are critical for on-field deployment. A custom integrated feedback system consisting of a laser diode and a position-sensing detector was developed to investigate the impact of the resonant frequency of the MEMS and the driving signal of the scanner on the movement of the mirror. Results on the metrology of manufactured materials and characterization of tissue samples with GD-OCM are presented.

Thickness estimation, which has a broad range of applications, plays an important role in the field of optical metrology. In this study, we investigate a new approach—combining optical coherence tomography (OCT) and statistical decision theory—for thickness estimation. We first discussed and quantified the intensity noise of three commonly used broadband sources, a super-continuum source, a super-luminescent diode (SLD), and a swept source. Furthermore, a maximum-likelihood (ML) estimator was implemented to interpret the OCT raw data. Based on the mathematical model and the ML estimator, simulations were set up to investigate the impact of different broadband sources in OCT for a thickness estimation task. We then validated the theoretical framework with physical phantoms. Results demonstrate unbiased nanometer-class thickness estimates with the ML estimator. The framework can be potentially used for film and surface shape metrology.

Optical Coherence Tomography (OCT) applications can be divided into biomedical and industrial, the latter covering non-destructive testing of non-reflective materials (e.g. optical glass) or for profilometry of metallic surfaces. Irrespective of the areas mentioned above, it is important to translate the technology from lab to clinical and industrial environments, depending on the case. This paper presents handheld probes with 1D galvoscanners developed in our groups to achieve this goal. These probes have been designed to be as simple, light weight, and low-cost as possible. Their optomechanical construction is described in different variants. Advantages regarding galvoscanners use are discussed, as compared to probes equipped with MEMS. The optomechanical aspects are completed with a discussion on optical design and on other scanning systems that may be utilized in such probes. Several applications of the probes developed are presented, such as in optical metrology.

This paper will list some items to consider during the initial lens design phase that will expedite later fabrication, with items applicable to any lens type.

Sensitivity to tolerances is a well-known problem in optical design. In many cases, multiple designs having different tolerance sensitivities will solve the optical design problem. Often, the solution with the best “as-designed” performance is not the solution with the best “as-built” performance. In the end, it is not the as-designed quality of the optics that matters; it is only the as-built quality that matters. As we demonstrate in this paper, typical merit functions used in optimization (e.g., RMS spot diameter or RMS wavefront variance of the pre-tolerance system) are often poorly correlated to actual, as-built image quality; in many cases the correlation is extremely poor. One known strategy to avoid this is to add something to the merit function that penalizes design forms that are particularly sensitive. The ultimate success of a merit function is determined by the extent to which it correlates with as-built performance. Such a strategy is of particular importance during a global optimization design phase, in which the optimizer will generate many different design forms, some of which may differ significantly from the starting design, both in appearance and in tolerance sensitivity. In this paper we examine the addition of a “sensitivity” parameter to the merit function. We discuss the selection of the weighting factor for the sensitivity parameter, as well as the correlation of the merit function (both with and without the sensitivity parameter) to as-built performance.

The range of aspheres that may be designed is larger than the range of aspheres that may be successfully measured and manufactured. This can lead to frustration for both the optical designer and the optical fabricator. Available polishing tools impose some limitations; full-aperture interferometry imposes other limitations. The optical designer must include constraints in the merit function to encourage the design to respect these limitations if manufacturing is to proceed smoothly. The aspheric surface curvature plot provides key information to understanding which constraints must be added to the merit function to encourage the asphere designs to stay within the portion of solution-space that may be manufactured and measured. There is often little or no performance penalty due to adding these constraints.

At the 1994 International Optics Design Conference, a paper was presented by the author that proposed that optics costs are often driven by the fabrication and assembly tolerances. In addition, that these tolerances fall into groups (classes) that for any given shop are set typically by the capital investment in measurement equipment that the shop has access to. The premise is then that it is essential that the optical system tolerances on fabrication, e.g. radii, element thickness, wedge, surface figure, and surface finish and on assembly e.g. component tilt and decenter and spacer thickness and wedge that are assigned by the optical designer be self-consistent with the capabilities of the shops that are solicited to provide a quotation.

In the 1994 paper, five classes of optical fabricators were identified; catalog, regular, select, premium, and ultimate (lithography). For each of these classes, representative minimum tolerances were published along with estimates of the cost increment. An important concept is that if any one tolerance falls into a tighter class, then the optical system must be built in a shop capitalized to provide that one minimum tolerance and as a result all the other tolerances can typically be moved to the tighter class with little cost impact. The primary cost impact then is driven by the class of shop dictated by the minimum tolerance. In this talk, a primary purpose is to revisit the tolerances associated with a given class of shop and update the numbers to reflect advances in the intervening two decades.

In support of the Extreme Ultraviolet Lithography (EUV, EUVL) roadmap, a joint program between Zygo Corporation and SEMATECH is under way to develop 13.5 nm, 0.5NA R&D photolithography tools with small fields. Those tools are referenced as micro-field exposure tools, or METs. Previous papers^1,2,3 have focused on the design and theoretical performance and the fabrication and testing of the optical components.

In this paper, results from the completed projection optic box (PO, POB) systems are presented. The achieved single pass transmitted wavefront (CA – 30 cycles/aperture) on the first two systems was better than 0.25nm RMS at the center of the field and < 0.48nm RMS over the 30um x 200um field, less than half of the original specification. The flare, as calculated from the component roughness data, is less than the 5% specification.

The paper includes a presentation of results from the component mirror metrology, the multilayer coatings, and the system metrology. To support the tight specifications, the component and system metrology tests required test reproducibility on the order of <50pm. To achieve the high quality wavefront, the optic mounts had to produce very small surface deformation. Also, the precision and stability of the alignment had to be controlled to a few tens of nanometer. The mirror motion is controlled by a hexapod system and the processes and mechanics that were used to align the POB will be described. Results of alignment convergence, wavefront error at the center of the field and over the field, as well as reproducibility are presented.

Zemax has developed an XML schema for the distribution of singlet lens specifications based on the ISO 10110 standard. In OpticStudio 15, this kind of XML data can be exported from the ISO Element Drawing analysis. The data file is then used in a feature that automates exchange of lens data between designer and manufacturer, the Cost Estimator. This Cost Estimator feature submits the XML data to various manufacturers to obtain cost estimates for prototype lens production. The workflow centered on the XML data exchange facilitates rapid cost estimate retrieval and eliminates the need for redundant manual data entry.

The XML Schema Definition (XSD) for the XML format can be used with Microsoft developer tools to automatically create .NET classes to serialize and deserialize the singlet lens data to/from XML files. The format provides flexible unit specification for most parameters. Choosing XML as the basis for the file format has provided several benefits, such as the above mentioned automated serialization capabilities in .NET, a human-readable text-based format, and ready support for consumption by web services.

Especially in the area of the large mirror manufacturing only a few manufacturers are capable to produce optical surfaces of high quality. Therefore a deterministic process should be developed in the project IFasO. In the field of telescope optics off-axis optical systems are becoming increasingly important. These systems try to avoid an obstructing of the incoming light by moving the secondary mirror out of the primary mirror's optical axis. This advantage leads to an increasing market for this type of optical surface.

Until now off-axis mirrors were difficult or almost impossible to produce. With the processes developed in IFasO, high quality mirrors become possible. For this reason, this paper describes the manufacturing of off-axis surfaces and its problems.

The mirror production used in the project IFasO is based on the specific design of the CNC center developed by the company Optotech. This center UPG2000 is capable of grinding, polishing, sagitta measurement and interferometric measurement in one mounting of the specimen. Usually a large optics has to be transported during their manufacturing after every individual process step. There is always a risk of damage of the specimen. The exact orientation of the surface relatively to the tool position is also required. This takes a huge amount of time and makes up most of the production time.

In this presentation the use of UPG2000 and the next steps within the process development are described. In the current status the manufacturing of large off-axis elements with a PV < λ/10 rms is reproducible.

The Richard F. Caris Mirror Lab is in the process of fabricating 8.4 meter mirror segments for the Giant Magellan Telescope. Seven of the segments are off-axis with 14 mm of aspheric departure. In order to successfully fabricate these mirrors we are constantly taking steps towards faster, more deterministic methods, from diamond generating to stressed lap polishing. The Large Optical Generator (LOG) is celebrating its 30-year anniversary at the University of Arizona with a complement of technological updates and enhancements. This paper shows how some of these upgrades will aid in the manufacture of the GMT segments.

Large, lightweight mirrors are a critical component in space based imaging applications. These mirrors have traditionally required long manufacturing cycle times with associated high costs. In this paper, the key cost and schedule drivers for the production of large, lightweight mirrors will be reviewed along with enabling solutions that could provide significant cost and schedule reductions while maintaining the high quality performance required for these challenging applications. The technologies include advancements in replication, construction, and bonding. Initial feasibility tests and associated results will be presented.

In an optical coating, the thin film engineer must control film thickness and index of refraction to achieve high optical coating performance. While film thickness can generally be controlled with sweeps, sources, and distribution shields, index can be a tougher problem to solve. Often times, contaminants affect the index of refraction of a thin film and cause variations within different portions of the coating chamber leading to poor yield. Presented here is a methodology and case study used to diagnose index of refraction non-uniformity as well as identify the potential sources of contaminants in the system using a combination of Residual Gas Analysis and Secondary Ion Mass Spectrometry.

Ultra-precise metal optics are key components of sophisticated scientific instrumentation in astronomy and space applications, covering a wide spectral range. Especially for applications in the visible or ultra-violet spectral ranges, a low roughness of the optics is required. Therefore, a polishable surface is necessary. State of the art is an amorphous nickel-phosphorus (NiP) layer, which enables several polishing techniques achieving a roughness of <1 nm RMS. Typically, these layers are approximately 30 μm to 60 μm thick. Deposited on Al6061, the bimetallic effect leads to a restricted operational temperature, caused by different coefficients of thermal expansion of Al6061 and NiP. Thinner NiP layers reduce the bimetallic effect. Hence, the possible operating temperature range. A deterministic shape correction via Magnetorheological Finishing of the substrate Al6061 leads to low shape deviations prior to the NiP deposition. This allows for depositing thin NiP-layers, which are polishable via a chemical mechanical polishing technique aiming at ultra-precise metal optics. The present article shows deposition processes and polishability of electroless and electrolytic NiP layers with thicknesses between 1 μm and 10 μm.

The assembly effort of an optical system naturally relies on the degrees of freedom and the maximum allowable tolerances each optical surface introduces into the overall budget. Snap-together approaches traditionally can be regarded as attractive solutions for IR systems having moderate tolerances, where the required precision is achieved by simultaneously machining optical surfaces and mounting interfaces in a single machine setup. Recent improvements in manufacturing and metrology enable a transfer of the assembly approach to shorter wavelength applications, where sub-aperture figuring techniques are used in combination with suitable amorphous polishing layers to achieve the increased requirements on figure and finish. A further decrease of the assembly effort is gained by machining several optical surfaces on common mechanical substrates and fixing the relative position with uncertainties as low as the machine precision. The article presents the fabrication of large electroless nickel coated aluminum mirror modules having two functional freeform surfaces and references for metrology and system integration. The modules are part of an all metal anamorphic imaging telescope operating in the visual spectral range. Presented methods open up a rapid and reliable assembly of metal mirror based VIS telescopes to be used in ground and space based astronomy or remote sensing applications.

Today's optical systems require up-to-date assembly and joining technology. The trend of keeping dimensions as small as possible while maintaining or increasing optical imaging performance leaves little to no room for mechanical lens adjustment equipment that may remain in the final product. In this context active alignment of optical elements opens up possibilities for the fast and cost-economic manufacturing of lenses and lens assemblies with highest optical performance.

Active alignment for lens manufacturing is the precise alignment of the optical axis of a lens with respect to an optical or mechanical reference axis (e.g. housing) including subsequent fixation by glue. In this contribution we will describe different approaches for active alignment and outline strengths and limitations of the different methods. Using the SmartAlign principle, highest quality cemented lenses can be manufactured without the need for high precision prealignment, while the reduction to a single alignment step greatly reduces the cycle time. The same strategies can also be applied to bonding processes. Lenses and lens groups can be aligned to both mechanical and optical axes to maximize the optical performance of a given assembly. In hybrid assemblies using both mechanical tolerances and active alignment, SmartAlign can be used to align critical lens elements anywhere inside the system for optimized total performance. Since all geometrical parameters are re-measured before each alignment, this process is especially suited for complex and time-consuming production processes where the stability of the reference axis would otherwise be critical. For highest performance, lenses can be actively aligned using up to five degrees of freedom. In this way, SmartAlign enables the production of ultra-precise mounted lenses with an alignment precision below 1 μm.

The transmission sphere (TS) provides a high-quality reference wavefront which is common path with a test wavefront to generate interference fringes in a Fizeau interferometer. The optical path difference (OPD) of the reference wavefront should be controlled within peak-to-valley (PV) 5 λ (λ=0.6328 um), because too large OPD makes interference fringes distorted. Therefore, the tolerance analysis of the reference wavefront is very critical. Because the surface irregularity of lens can change the phase of a wavefront, surface deformation after mounting highly impacts on the wavefront error. For large optics, such as φ 6-inch in this study, surface deformation dominates the quality of the reference wavefront. For minimizing surface deformation after mounting, semi-kinematic mounting technology is used in sub-cells design to avoid over-constraint forces and unpredictable deformation. Then, the deformation due to gravity force of each surface can be constrained around PV 0.3 λ with Zernike trefoil in vertical setup TS; however, the superposition of the distorted wavefront may deteriorate the optical performance. A method of optimizing orientation of each lens around optical axis is presented in this paper. Sub-cells are designed to be rotational around optical axis respectively. The wavefront error of the reference beam of the worst case is improved significantly after optimization. Consequently, the method can effectively reduce the difficulty of lenses fabrication and mounting, and then the specification of the surface irregularity can be lower for cost saving. Based on the optimization in our study, a good reference wavefront can be acquired without any tight tolerance or complicated assembly.

With the recent advances in optical fabrication technology, the manufacturing of freeform optical surfaces is no longer prohibitive. To spur the development of freeform systems, however, optical designers must be given the necessary tools to efficiently design, analyze, and tolerance these systems. The process for designing freeform imaging systems is enhanced by the knowledge of the individual aberration contributions across the full field-of-view. As shown in the recent aberration theory for freeform surfaces, identifying the field dependence of the dominant aberrations is critical for a controlled freeform optimization. Coma, an often system-limiting aberration and an aberration that has recently been directly addressed with freeform surfaces, is of specific interest. Currently, a coma full-field display (FFD) of a system can be generated in commercial ray-tracing software by fitting the wavefront at the exit pupil with Zernike polynomials, but this process can involve tracing thousands of rays. Moreover, the circular coma FFDs are inherently separate from the elliptical coma FFDs. In this research, we use nodal aberration theory to develop a method to generate a coma FFD that requires only a few (less than 10) rays per field point to be traced through the optical system. Both the magnitude and orientation of the coma aberrations at the image plane are shown in our FFDs, including the effects of elliptical coma. These coma FFDs save computation time during the design and offer valuable insight to the designer. Examples of the plots will be shown for multiple freeform optical systems.

As freeform optical systems emerge as interesting and innovative solutions for imaging in 3D packages there is an assumption they are going to be more sensitive particularly at assembly. While it is true that the clocking of the component becomes a relatively weak new tolerance, for the most effective new class of freeform systems the alignment sensitivity is actually lower in most cases than for a comparable traditional unobscured three mirror anastigmatic (TMA) telescope.

Traditional unobscured TMA telescopes, whose designs emerged in the mid-70s and which begin to appear as hardware in the literature in the early 90s, are based on using increasingly offset apertures with otherwise coaxial rotationally symmetric mirrors. The mirrors (typically 3 to correct spherical, coma, and astigmatism) have evolved to contain more high order terms as the designs are pushed to more compact and wider field packages – the NIRCAM camera for the JWST is an excellent example of this [1]. As the higher order terms are added, the mirrors become increasingly sensitive to decenters and tilts.

An emerging class of freeform telescopes that provide wider field of view and/or faster f/numbers than the traditional TMA are based on a strategy where the surface shape remains a low order Zernike-type surface even in compact, unobscured packages. This optical design strategy results in an optical form that is not only higher performance but simultaneously less sensitive to alignment.

Freeform optical surfaces, which have little to no symmetry, are gaining popularity with lens designers and optical system integrators. These freeform optics can enhance optical performance by reducing the number of elements, enabling lighter and more efficient systems, and by reducing aberrations. Most traditional manufacturing techniques cannot yield polished freeform optical surfaces. Likewise, traditional metrology equipment has difficulty accurately measuring the deviation of freeform surfaces from their nominal shape, the surface form error. The inclusion of mechanical fiducials on freeform optics can ease some of this difficulty. Well placed fiducials can provide alignment features for contact metrology equipment such as coordinate measuring machines (CMMs). Mechanical fiducials allow for precise locating of all surfaces of an optic in reference to one another and provide a reference from which the freeform surface can be measured against. This allows a CMM to output the deviation of a surface from its nominal shape, as well as the wedge and center thickness of the optic. Alignment fiducials also enable more precise locating of the surface during the manufacturing process, shortening the time required for production and lowering the cost of fabricating freeform optics. This paper will explore the advantages of including locating fiducials on freeform optics and how they can aid in the manufacture and measurement of optical surfaces.

The strategy for measuring and analyzing freeforms with a new high precision cylinder coordinate measuring instrument equipped with an optical point sensor is presented. As freeforms compared to aspheres are not rotationally symmetric considering outline and shape the measuring process has to be designed in new ways. In addition fiducials on the sample or fixture have to be measured to determine position and orientation, i.e. a coordinate system, of the sample. In the following analysis process this coordinate system has to be taken into account. The performance of the measuring instrument is demonstrated and measuring results of different samples are shown.

The recent advances in the optics manufacturing industry to achieve the capability of fabricating rotationally nonsymmetric optical quality surfaces have considerably stimulated the optical designs with freeform components. This opens up new horizons for novel optical systems with larger fields of view and higher performance, or significantly more compact in volume at equal performance compared to conventional systems. A bottleneck to the broad industrial applications of freeform optics remains the lack of a high performance optical metrology tool capable of measuring significant surface departures and slopes of the parts. To address this issue, we have developed a fiber-based swept-source optical coherence tomography (SS-OCT) system for point-cloud freeform metrology, where two-axis galvanometer scanners are leveraged for high-speed lateral scans. We specifically designed a custom all-reflective achromatic pupil relay system to achieve a diffraction-limited scanning configuration. Coupled with a large field-of-view (FOV) telecentric scan lens, the imaging covers 28.9 mm × 28.9 mm FOV with 35 μm lateral resolution and more than 600 μm depth of focus. Freeform metrology is demonstrated for an Alvarez surface of 400 μm surface sag. The high sensitivity of the SS-OCT system allows for capturing the slope variations of the part up to the maximum slope that is 5 degrees in this case. Specific surface reconstruction, rendering and fitting algorithms were developed to evaluate the metrology results and investigate the accuracy and precision of the measurements.

In recent years, demand for an optical element having a high degree of freedom shape is increased. High-precision aspherical shape is required for the X-ray focusing mirror etc. For the head-mounted display etc., optical element of the free-form surface is used. For such an optical device fabrication, measurement technology is essential. We have developed a high- precision 3D nanoprofiler. By nanoprofiler, the normal vector information of the sample surface is obtained on the basis of the linearity of light. Normal vector information is differential value of the shape, it is possible to determine the shape by integrating. Repeatability of sub-nanometer has been achieved by nanoprofiler. To pursue the accuracy of shapes, systematic error is analyzed. The systematic errors are figure error of sample and assembly errors of the device. This method utilizes the information of the ideal shape of the sample, and the measurement point coordinates and normal vectors are calculated. However, measured figure is not the ideal shape by the effect of systematic errors. Therefore, the measurement point coordinate and the normal vector is calculated again by feeding back the measured figure. Correction of errors have been attempted by figure re-derivation. It was confirmed theoretically effectiveness by simulation. This approach also applies to the experiment, it was confirmed the possibility of about 4 nm PV figure correction in the employed sample.

A new capability for simultaneously generating micro-structures and large freeform surfaces has been developed. Multiple axes of CNC coordinated motion have been integrated into an ultra precision machine platform, enabling a wide variety of optical mold masters to be created. Facilitated by a specially developed control system, freeform optical surfaces as large as 600 x 600 x 100 mm are possible. Some machine alignments are critical to the production of accurate parts and these will be discussed. A bridge construction reduces Abbe offsets, and oil hydrostatic linear slide ways provide sub-micron straightness. The linear axes are capable of accurate positioning by means of linear motors in combination with the non contact oil hydrostatic slide ways. Optical surface finishes are achieved with the stability of a large granite base supported by a high performance vibration isolation system. The machine includes a unique, self-compensating, patented oil bearing rotary axis. Critical machine errors are measured and corrected with integrated CNC machine compensation. The machine has accuracy and repeatability for the creation of precise, intersecting groove structures with multiple angles over large areas. Optical surfaces can be generated either by a ruling/shaping operation with a non-rotating tool, or by a flycutting tool rotating on a high speed air bearing spindle. The spindle can double as a positioning axis to generate variable angle grooves in ruling mode. A Fast Tool Servo can be utilized to create fine micro-structures. Work piece quality can be evaluated in-situ with metrology sensors.

Aspheric cylinders have the ability to improve optical performance over standard cylindrical surfaces. Over the last several years there has also been development into the application and functionality of utilizing freeform surfaces to improve optical performance. Freeforms have the ability to not only improve image quality over a greater field of view, but can open up the design space of an optical system making it more compact. Freeform geometries, much like aspheric cylinders, may not have an axis of rotation to spin the optic about during manufacturing. This leads to costly fabrication processes and custom metrology set ups, which may inhibit their use.

Over the last several years, OptiPro Systems has developed and optimized our eSX grinding, UFF and USF polishing, UltraSurf metrology, and ProSurf software programming technologies to make the processing of these complex geometries much easier and deterministic. In this paper we will discuss the challenges associated with manufacturing complex shapes like aspheric cylinders as well as freeform geometries, and how several technologies working together can overcome them. The technologies focus on metrology feedback to a grinding and polishing machine that is controlled through an iterative computer aided manufacturing software system. We will also present examples of these hard to manufacture shapes with results.

Increasingly freeform prototypes and molds for high volume replication are being manufactured using diamond machining. Nevertheless, stroke limits of established fast tools require using time consuming slow tool processes reducing productivity. Further, freeform measurements require high efforts. The UPC 400 overcomes these limitations. Utilizing a fast tool with an industry leading stroke length permits machining a wide range of freeform optics in the shortest time while increasing productivity and accuracy. Machine integrated, optical metrology allows for comfortable freeform measurements without having to remove the optic. Besides precise measurements, this enables corrective machining to create surfaces of the highest quality.

The blistering pace of recent technological advances has led lens designers to rely increasingly on freeform optical components as crucial pieces of their designs. As these freeform components increase in geometrical complexity and continue to deviate further from traditional optical designs, the optical manufacturing community must rethink their fabrication processes in order to keep pace. To meet these new demands, Optimax has developed a variety of new deterministic freeform manufacturing processes. Combining traditional optical fabrication techniques with cutting edge technological innovations has yielded a multifaceted manufacturing approach that can successfully handle even the most extreme freeform optical surfaces.

In particular, Optimax has placed emphasis on refining the deterministic form correction process. By developing many of these procedures in house, changes can be implemented quickly and efficiently in order to rapidly converge on an optimal manufacturing method. Advances in metrology techniques allow for rapid identification and quantification of irregularities in freeform surfaces, while deterministic correction algorithms precisely target features on the part and drastically reduce overall correction time. Together, these improvements have yielded significant advances in the realm of freeform manufacturing. With further refinements to these and other aspects of the freeform manufacturing process, the production of increasingly radical freeform optical components is quickly becoming a reality.

Recently, the desire to use freeform optics has been increasing, including shapes such as torics and anamorphic aspheres. Freeform optics can be used to expand capabilities of optical systems. They can compensate for limitations in rotationally symmetric optics. These same traits that give freeform optics the ability to improve optical systems also makes them more challenging to manufacture. This holds true for grinding, polishing, and metrology. As freeform optics become more prevalent in the industry, tolerances will become more stringent, requiring deterministic manufacturing processes.

To generate freeforms, it is crucial to have control over all aspects of the process. Controlling the surface definition is important for achieving a better surface finish during processing. Metrology will be required to adjust tool paths at various stages in manufacturing. During grinding, metrology will be used to adjust tool positions relative to the nominal tool path to compensate for repeatable machine and tooling error. For polishing, metrology will be used to deterministically adjust dwell relative to the amount of the error in different surface locations, allowing for convergence towards the desired surface at a uniform rate.

OptiPro has developed PROSurf, a CAM software package for creating freeform tool paths and applying metrology-based corrections. The software can be used for both grinding and polishing freeform optics. The software has flexibility to allow for different methods of modelling the surface: mathematical equations, solid models, and point clouds. The software is designed to make it easier to manufacture and polish complex freeform optics.

Silicon is an optical material widely used in the production of infrared optics. However, silicon as a brittle material exhibits some difficulties when ultra-precision machined by mono-crystalline single point diamond. Finish turning of silicon with mono- crystalline diamond inserts results in accelerated tool wear rates if the right combination of the machining parameters is not properly selected. In this study, we conducted a series of machining tests on an ultra-high precision machine tool using finish turning conditions when using mono-crystalline diamond inserts with negative rake angle and relatively big nose radius. The study yields some recommendations on the best combination of machining parameters that will result in maximum material removal rates with smallest possible surface finish. In this work, standard non-controlled waviness diamond inserts having nose radius of about 1.5 mm, rake angle of negative 25°, and clearance angle of 5° were used to produce flat surfaces on silicon disk. From the results, it has been established that feed rate has the most influential effect followed by the depth of cut and cutting speed.

Traditional optical aluminium grades such as Al 6061 are intensively used for making optical components for applications ranging from mould insert fabrication to laser machine making. However, because of their irregular microstructure and relative inhomogeneity of material properties at micro scale, traditional optical aluminium may exhibit some difficulties when ultra-high precision diamond turned. Inhomogeneity and micro-variation in the material properties combined with uneven and coarse microstructure may cause unacceptable surface finish and accelerated tool wear, especially in grooving operation when the diamond tool edge is fully immersed in the material surface. Recently, new grades of optical aluminium that are featured by their ultra-fine microstructure and improved material properties have been developed to overcome the problem of high tool wear rates. The new aluminium grades have been developed using rapid solidification process which results in extremely small grain sizes combined with improved mechanical properties. The current study is concerned with investigating the performance of single-point diamond turning when grooving two grades of rapidly solidified aluminium (RSA) grades: RSA905 which is a high-alloyed aluminium grade and RSA443 which has a high silicon content. In this study, two series of experiments employed to create radial microgrooves on the two RSA grades. The surface roughness obtained on the groove surface is measured when different combinations of cutting parameters are used. Cutting speed is varied while feed rate and depth of cut were kept constant. The results show that groove surface roughness produced on RSA443 is higher than that obtained on RSA905. Also, the paper reports on the effect of cutting speed on surface roughness for each RSA grade.

One lens at a time on axis diamond turning or grinding of lens arrays with a large number of lenses is conventionally impractical because of the difficulties to shift and balance the substrate for each lens position. A novel method for automatic indexing was developed. This method uses an innovative mechatronics tooling (patent pending) that allows dynamic indexing at constant work spindle speed for maximum productivity and thermal stability of the work spindle while the balancing condition is maintained. In this paper we shall compare the machining capabilities of this method to free-form machining techniques, discuss about the main issues, present the concept and design of the working prototype and specific test bed, and present the results of the first cutting tests.

Finished lens molding, and the similar process of precision lens molding, have long been practiced for high volume, accurate replication of optical surfaces on oxide glass. The physics surrounding these processes are well understood, and the processes are capable of producing high quality optics with great fidelity. However, several limitations exist due to properties inherent with oxide glasses. Tooling materials that can withstand the severe environmental conditions of oxide glass molding cannot easily be machined to produce complex geometries such as diffractive surfaces, lens arrays, and off axis features. Current machining technologies coupled with a limited selection of tool materials greatly limits the type of structures that can be molded into the finished optic.

Tooling for chalcogenide glasses are not bound by these restrictions since the molding temperatures required are much lower than for oxide glasses. Innovations in tooling materials and manufacturing techniques have enabled the production of complex geometries to optical quality specifications and have demonstrated the viability of creating tools for molding diffractive surfaces, off axis features, datums, and arrays. Applications for optics having these features are found in automotive, defense, security, medical, and industrial domains.

This paper will discuss results achieved in the study of various molding techniques for the formation of positive diffractive features on a concave spherical surface molded from As2Se3 chalcogenide glass. Examples and results of molding with tools having CTE match with the glass and non CTE match will be reviewed. The formation of stress within the glass during molding will be discussed, and methods of stress management will also be demonstrated and discussed. Results of process development methods and production of good diffractive surfaces will be shown.

Advancements in optical manufacturing technology allow optical designers to implement steep aspheric or high departure surfaces into their systems. Accurate metrology during the grinding and polishing stages of asphere manufacturing will reduce time and cost. Measuring these surfaces with common interferometers or profilometers can be difficult due to large surface slopes or unpolished surface texture. OptiPro has developed UltraSurf to qualify the form, figure, and thickness of steep aspheric and freeform optics. UltraSurf is a computer controlled, non-contact coordinate measuring machine. It incorporates five air-bearing axes, linear motors, high-resolution feedback, and a non-contact probe. The measuring probe is scanned over the optical surface while maintaining perpendicularity and a constant focal offset. There are multiple probe technologies available on UltraSurf, and each probe has strengths and weaknesses relative to the material properties, surface finish, and figure error of an optical component. Validation of the system accuracy, repeatability, and methodology must be performed to trust the measurement data. Form and figure maps of a flat, a sphere, and an asphere using UltraSurf will be presented with comparisons to interferometry. In addition, accuracy, repeatability, and machine qualification will be discussed.

To obtain higher spatial resolution interferometric measurements, users of optical shop interferometers generally want to obtain the highest possible number of pixels in the field of view. When the optical surface being tested does not fill the interferometer’s field of view, zoom optics in the viewing system can provide a convenient means to fill the detector. Some users employ zoom to measure subapertures of a larger optical surface to observe mid-spatial frequency (MSF) features that may not be seen in a full aperture test. While the zoom obviously enables the detector to be filled, its capability to increase the MSF measurement performance of the instrument is more difficult to assess.

To investigate how zoom affects the MSF measurement capability, we measured a spherical surface with significant MSF content over a range of lateral magnifications. Two methods were used to obtain equivalent lateral magnifications: zoom and changing the transmission sphere. Differences in the relative MSF content were observed between the two methods. For further comparison, the same surface was measured with the same transmission spheres on a different interferometer with a fixed magnification coherent viewing system. We report on differences observed in measured MSF content between the two interferometers.

A method for non-contact 3D form testing of aspheric surfaces including determination of decenter and wedge errors and lens thickness is presented. The principle is based on the absolute measurement capability of multi-wavelength interferometry (MWLI). The approach produces high density 3D shape information and geometric parameters at high accuracy in short measurement times. The system allows inspection of aspheres without restrictions in terms of spherical departures, of segmented and discontinuous optics. The optics can be polished or ground and made of opaque or transparent materials.

In this work, we show a simple device that helps in the use of the sub-aperture stitching method for testing convex surfaces with large diameter and a small f/#. This device was designed at INAOE’s Optical work shop to solve the problem that exists when a Newton Interferometer and the sub-aperture stitching method are used. It is well known that if the f/# of a surface is small, the slopes over the surface increases rapidly and this is critical for points far from the vertex. Therefore, if we use a reference master in the Newton interferometer to test a convex surface with a large diameter and an area far from the vertex, the master tends to slide causing scratches over the surface under test. To solve this problem, a device for mounting the surface under test with two freedom degrees, a rotating axis and a lever to tilt the surface, was designed. As result, the optical axis of the master can be placed in vertical position avoiding undesired movements of the master and making the sub-aperture stitching easier. We describe the proposed design and the results obtained with this device.

A non-null annular subaperture stitching interferometry (NASSI), combining the subaperture stitching idea and non-null test method, is proposed for steep aspheric testing. Compared with standard annular subaperture stitching interferometry (ASSI), a partial null lens (PNL) is employed as an alternative to the transmission sphere, to generate different aspherical wavefronts as the references. The coverage subaperture number would thus be reduced greatly for the better performance of aspherical wavefronts in matching the local slope of aspheric surfaces. Instead of various mathematical stitching algorithms, a simultaneous reverse optimizing reconstruction (SROR) method based on system modeling and ray tracing is proposed for full aperture figure error reconstruction. All the subaperture measurements are simulated simultaneously with a multi-configuration model in a ray-tracing program, including the interferometric system modeling and subaperture misalignments modeling. With the multi-configuration model, full aperture figure error would be extracted in form of Zernike polynomials from subapertures wavefront data by the SROR method. This method concurrently accomplishes subaperture retrace error and misalignment correction, requiring neither complex mathematical algorithms nor subaperture overlaps. A numerical simulation exhibits the comparison of the performance of the NASSI and standard ASSI, which demonstrates the high accuracy of the NASSI in testing steep aspheric. Experimental results of NASSI are shown to be in good agreement with that of Zygo® Verifire^TM Asphere interferometer.

A model-based phase-shifting interferometer (MPI) is developed, in which a novel calculation technique is proposed instead of the traditional complicated system structure, to achieve versatile, high precision and quantitative surface tests. In the MPI, the partial null lens (PNL) is employed to implement the non-null test. With some alternative PNLs, similar as the transmission spheres in ZYGO interferometers, the MPI provides a flexible test for general spherical and aspherical surfaces. Based on modern computer modeling technique, a reverse iterative optimizing construction (ROR) method is employed for the retrace error correction of non-null test, as well as figure error reconstruction. A self-compiled ray-tracing program is set up for the accurate system modeling and reverse ray tracing. The surface figure error then can be easily extracted from the wavefront data in forms of Zernike polynomials by the ROR method. Experiments of the spherical and aspherical tests are presented to validate the flexibility and accuracy. The test results are compared with those of Zygo interferometer (null tests), which demonstrates the high accuracy of the MPI. With such accuracy and flexibility, the MPI would possess large potential in modern optical shop testing.

Optical materials and lens assemblies are specified for use at various operating temperatures. Ophthalmic lenses such as intra-ocular (IOLs), rigid gas permeable (RGP), and soft contact lenses must be verified at a single well-controlled temperature to ensure correct performance. In comparison, lens assemblies for UAVs (unmanned aerial vehicles) and other “outdoor” applications demand performance over a substantial range of temperatures. Both applications demand the ability to integrate temperature monitoring or control with optical measuring instruments. A common practice is to thermally soak the material or lens assembly and then attempt measurement before the object under evaluation returns to ambient room temperature. We are reporting on the utilization of a NIST-traceable temperature device combined with wavefront sensing technology for faster integrated measurement capability. The temperature sensor is currently capable of 0.01 and 0.1 degree C resolution and accuracy; respectively for an operating range of 0 to 100 degrees C. Efforts are underway to extend the temperature measurement range down to -30 C. The wavefront measurement device is a Shack- Hartmann sensor (SHS) operating at 5 to 15 Hz with simultaneous gauging of temperature. The SHS can be operated with a choice of wavelengths from 400 to 1,000 nm. It also supports both single and double-pass configurations. The single-pass arrangement was chosen for these experiments due to the simpler, more compact set-up. The dynamic range of the wavefront sensor is first utilized to evaluate the temperature chamber. Results are then presented for two lens assemblies intended for commercial UAVs.

We present various applications of Quadri Wave Lateral Shearing Interferometry to infrared optical metrology. Phasics has developed wave front sensors compatible with wavelengths ranging from 193nm to 14 μm. Several camera technologies are integrated with patented diffractive optics adapted to the various spectral ranges. In the infrared range, InGaAs, MCT and microbolometers are used as light sensors. We developed a bench to qualify lenses with diameter from 2mm to 100mm in the LWIR spectral range. Thanks to an innovative ray-trace algorithm, we are able to compare the wave front measurement to the optical design enabling a feedback between lens manufacture and design. We also developed a VSWIR wave front sensor with a constant accuracy from 0.4μm to 1.7 μm. It also includes the Extended Tilt feature that enables sub-mrad accuracy on tilt measurement over a range of more than +-30°.

We present a metrology bench used to benchmark the optical quality of lenses used in automotive applications. These lenses have a wide field of view, typically larger than 180° and fast numerical apertures (F/2). Lenses are compared in terms of OPD and MTF. For this aim, interferometric solutions would require double-passing the lens. Between two field positions, it would be necessary to realign the reference sphere. This is not compatible with the requested high measurement throughput. Therefore wave front sensing is the best solution to this problem because it is able to characterize lenses in single pass configurations. We chose to measure the transmitted wave front with a QuadriWave Lateral Shearing Inferferometer wave front sensor placed directly after the focal plane. This technology is best suited in this case because it has the unique ability to measure fast diverging beams with high accuracy. It can also accept the large tilt angles due to the lens non telecentricity. Because the information needed for lens comparison is the OPD in the exit pupil, the wave front is then back-propagated to it thanks to an innovative ray-trace algorithm. This algorithm is also able to deduce the aperture transmission to take into account vignetting effects that appear at the field edges. Finally the MTF is simulated from the OPD and the pupil function. This bench is fully automated to rapidly benchmark a large number of lenses in their complete field of view. We characterized the bench according to the ISO 5725 standard. Its precision was tested with commercial lenses whereas trueness was assessed with calibrated lenses. The accuracy on MTF was found to be below 1% over the whole field of view.

Achromatic diffractive features on lenses are widely used in industry for color correction, however there is not a welldefined standard to quantify the performance of the lenses. One metric used to qualify a lens is the sag deviation from the nominal lens profile. Imperfections in the manufacturing of the diffractive feature may cause scattering and performance loss. This is not reflected in sag deviation measurements, therefore performance measurements are required.

There are different quantitative approaches to measuring the performance of an achromatic diffractive lens. Diffraction efficiency, a measure of optical power throughput, is a common design metric used to define the percent drop from the modulation transfer function (MTF) metric. The line spread function (LSF) shows a layout of the intensity with linear distance and an ensquared energy specification can be implemented. The MTF is a common analysis tool for assemblies and can be applied to a single element. These functional tests will be performed and compared with diffractive lenses manufactured by different tool designs.

This paper displays the results found with various instruments. Contact profilometry was used to inspect the profile of the diffractive elements, and a MTF bench was used to characterize lens performance. Included will be a discussion comparing the results of profile traces and beam profiles to expected diffraction efficiency values and the effects of manufacturing imperfections.

A table top instrument has been designed, constructed and tested to characterize all of the primary optical and physical properties of contact lenses. Measured optical properties include base power, cylinder power, cylindrical axis, prism, refractive index and wavefront aberrations. Measured physical properties include center thickness, lens diameter and lens sagittal depth. The instrument combines a Shack-Hartmann wavefront sensor (SHWS), a machine vision sensor, and a low coherence light interferometer (LCI) all coaxially aligned into a single tabletop unit. The unit includes a cuvette, mounted in a translatable sample chamber for holding the contact lens under test, and it can be configured to measure wet or dry contact lenses. During operation, the vision sensor measures the diameter of the lens, and locates the center of the lens. The lens is then aligned for other measurements. The vision sensor can also measure various alignment marks on the lens, as well as identify any alpha numerical features, which can be used to associate the lens orientation with the measured aberrations. The LCI measures the center thickness, sagittal depth and index of refraction of the contact lens. The base radius of curvature is then calculated using these measured parameters. The SHWS measures the lenses prescription power, including spherical, cylinder, prism, and higher order wavefront aberrations. NIST traceable calibration artifacts are used to calibrate the SHWS, machine vision and LCI modalities. Repeatability measurements on a contact lens in a saline solution are presented.

A Shack-Hartmann wave-front sensor system has been used to measure a set of plano-convex lenses at two different times, separated by almost 2 years. The plano-convex lenses were selected to cover a range of powers and apertures relevant to intraocular lenses, and were measured at two different orientations. The results demonstrate the high temporal stability of the measurement system, as well as of the glass standard.

In addition, both times the effective focal lengths of the standards were measured using a NIST traceable nodal slide bench, and the center thicknesses were measured using low-coherence interferometer. The spherical aberration and the effective focal length results are analyzed for statistically significant changes. The results are also compared to the Zemax models of the standards.

In this work we describe the use of Finite Element Analysis software to simulate the deformations of an optical mirror. We use Finite Element Method software as a tool to simulate the mirror deformations assuming that it is a thin plate that can be mechanically tensed or compressed; the Finite Element Analysis give us information about the displacements of the mirror from an initial position and the tensions that remains in the surface. The information obtained by means of Finite Element Analysis can be easily exported to a coordinate system and processed in a simulation environment. Finally, a ray-tracing subroutine is used in the obtained data giving us information in terms of aberration coefficients. We present some results of the simulations describing the followed procedure.

Small satellites are often used by spatial agencies to meet scientific spatial mission requirements. Their payloads are composed of various instruments collecting an increasing amount of data, as well as respecting the growing constraints relative to volume and mass; So small-sized integrated camera have taken a favored place among these instruments. To ensure scene specific color information sensing, pixelated filters seem to be more attractive than filter wheels. The work presented here, in collaboration with Institut Fresnel, deals with the manufacturing of this kind of component, based on thin film technologies and photolithography processes. CCD detectors with a pixel pitch about 30 μm were considered. In the configuration where the matrix filters are positioned the closest to the detector, the matrix filters are composed of 2x2 macro pixels (e.g. 4 filters). These 4 filters have a bandwidth about 40 nm and are respectively centered at 550, 700, 770 and 840 nm with a specific rejection rate defined on the visible spectral range [500 – 900 nm]. After an intense design step, 4 thin-film structures have been elaborated with a maximum thickness of 5 μm. A run of tests has allowed us to choose the optimal micro-structuration parameters. The 100x100 matrix filters prototypes have been successfully manufactured with lift-off and ion assisted deposition processes. High spatial and spectral characterization, with a dedicated metrology bench, showed that initial specifications and simulations were globally met. These excellent performances knock down the technological barriers for high-end integrated specific multi spectral imaging.

In this work, we describe the well-known methods of cutting and shaping for optical glass materials. These operations are very important in optical workshops and needs to be well defined at the beginning of the optical fabrication process. In this work we show the first steps to fabricate prism components for the MEGARA instrument that is being developed to work with the GRANTECAN. We present a review of the techniques used at INAOE´s Optical workshop for cutting blanks of optical glasses with an extensive use in optical fabrication; besides that, we present the process of shaping of these optical glasses just before they enter to the grinding and polishing processes. We present some results showing the described processes and some tips for the methods used in the optical workshop including the use of the necessary supplies, tools, and machinery.

An off-axis optical system can effectively avoid some problems, such as aberrations, shielded area created by the secondary mirror and a narrow field of view (FOV), while an on-axis optical system has the problems. Inspired by the consideration, the off-axis optical system is generally used for hyperspectral sensors and telescopes. However, there are several obstacles limiting the productivity of the off-axis optics in fabrication and measurement processes. In this study, to overcome this weakness, we suggests a new fabrication technique using a customized jig, not separated from the work-piece. A convex aspheric mirror and the off-axis mirror are fabricated by Single Point Diamond Turning Machine (SPDTM) for comparison analysis of surface state. The mirrors are made from aluminum (Al6061-T6) and used for the reflectors of a coastal water remote sensing system. We show fast machining and simple measurement in comparison with traditional off-axis single machining and measurement, provide performance results, such as form accuracy and surface roughness measured by both contact 3D profilometer (UA3P) and non-contact 3D profiler (CCI-Optics). The customized ultra-precision machining process can be effectively used for complex off-axis mirror fabricating.

Several mounting configurations could be applied to opto-mechanical design for achieving high precise optical system. The retaining ring mounting is simple and cost effective. However, it would deform the optics due to its unpredictable over-constraint forces. The retaining ring can be modified to three small contact areas becoming a semi-kinematic mounting. The semi-kinematic mounting can give a fully constrained in lens assembly and avoid the unpredictable surface deformation. However, there would be still a deformation due to self-weight in large optics especially in vertical setup applications. The self-weight deformation with a semi-kinematic mounting is a stable, repeatable and predictable combination of power and trefoil aberrations. This predictable deformation can be pre-compensated onto the design surface and be corrected by using CNC polisher. Thus it is a freeform surface before mounting to the lens cell. In this study, the freeform correction polishing is demonstrated in a Φ150 lens with semi-kinematic mounting. The clear aperture of the lens is Φ143 mm. We utilize ANSYS simulation software to analyze the lens deformation due to selfweight deformation with semi-kinematic mounting. The simulation results of the self-weight deformation are compared with the measurement results of the assembled lens cell using QED aspheric stitching interferometer (ASI). Then, a freeform surface of a lens with semi-kinematic mounting due to self-weight deformation is verified. This deformation would be corrected by using QED Magnetorheological Finishing (MRF® ) Q-flex 300 polishing machine. The final surface form error of the assembled lens cell after MRF figuring is 0.042 λ in peak to valley (PV).

The progress in the polishing of glass, in particular fused silica glass, with bound-abrasive is reviewed in the paper. The technique is rather successful in some respects, e.g. material removal rate, surface roughness, flatness of substrates. The surface roughness can be as low as <0.5nm (Ra) comparable with loose pad/pitch polishing for fused silica. On the other hand, the material removal rate is so high that the ground surface can be polished to specular (Ra:1~2nm) within a quarter of an hour. The technique can be adapted to polish plane, spherical, aspheric surfaces and even free-form surface. The technique is next to free of subsurface damage after slightly wet chemical etching. Because ceria is utilized as abrasives and epoxy resin as binding materials softer than or comparable to fused silica, the shape of the polishing tools is easy to be shaped and dressed and need no truing. The technique may provide a potential solution to fast polishing of glass.

In modern scientific and industrial laser applications, inter-alignment of multiple optical devices is frequently a basic requirement to meet a certain specification and performance. However, the designed optical system combining mechanical elements, lasers and optical sights in various wavelengths frequently deviates from specified goals due to real life imperfections and effects. These may include mechanical tolerances, optical distortion, heating, laser cavity misalignment, overall instabilities, and non-linear effects. In order to deliver accurately and produce intricate optical systems, a carefully designed method for inter-alignment is required completing and updating the already existing methods. Thus, we designed and upgraded the performance of electronic autocollimator and combined it with innovative mechanical manipulation of optical invariants such as a Lateral Transfer Hollow Periscope to greatly improve and expand inter-alignment procedures. Depending on the combination of optical sights, laser types, and mechanical requirements, an appropriate method will be analyzed. For example, several layouts will be analyzed such as high power CO₂ laser cavity alignment and laser delivery system mechanical rollers alignment. By completing the presented gear in this article other instruments such as Align Meter, Lateral Hollow Periscope (LTHPTM), Lateral Hollow Retroreflector ( LTHRTM) are available for applications such as alignment of articulated beam delivery systems.

A compact wavefront diagnosis system with nice repeatability based on the randomly encoded hybrid grating (REHG) is proposed. The REHG comes from the ideally calculated grating for quadriwave lateral shearing interference, and it consists of a binary amplitude grating and a phase chessboard. The phase chessboard simulates the phase modulation of the ideally calculated grating, while the binary amplitude grating is designed and fabricated based on the randomly encoding method. In this method, the amplitude distribution on the ideally calculated grating is firstly divided into discrete grids. And the radiant flux in each grid is quantized into several quantization levels. The binary amplitude grating is then generated by encoding the pixels in the grids with 1 and 0, which stands for whether the light can pass through or not, so that the total radiant flux in each grid on this grating approximate to the flux in the corresponding grid on the ideally calculated quadriwave grating. In addition, random pattern is employed in the encoding process to avoid introducing extra diffraction orders. The far-field diffractions of the REHG only contain the ±1 orders in two orthogonal directions, and no order selection mask is needed for quadriwave lateral shearing interference. Due to the common-path configuration, the wavefront testing results obtained by the REHG lateral shearing interferometer exhibits nice repeatability and good suppression over environmental noise and vibration.

The low intensity regions existed around the singular point of optical vortex (OV) beams influence the position detection accuracy of phase singular points, especially for OVs of large topological charge. A new method using Shack-Hartmann wavefront sensor (SH-WFS) is proposed to solve this problem. In the method, we combine several phase slopes obtained at individual lenses of a lens array into one to avoid the influence of the low intensity region and use correlation matching with pre-calculated simulation data to get the accurate singular point position. The experimental results show that the position detection precision of this method is maintained less than 0.2 in unit of lens-size for OVs of charges -20 to 20.

Focusing and imaging optics can be characterized by evaluating the wavefront error of the focused beam. We have bean developing a ptychographic phase retrieval method using a visible laser to measure the wavefront error. In this study, the measurement accuracy of the method is increased by improving both the phase retrieval algorithm and the experimental setup. The system is applied to the characterization of an ellipsoidal mirror used for the focusing of soft X-rays. The posture of the mirror can be measured with a resolution of 1.4 μrad. The wavefront error originating from the surface profile error can be detected with an accuracy of 0.01λ (root mean square).

Aspheric non-null test achieves more flexible measurements than the null test. However, the precision calibration for retrace error has always been difficult. A reverse optimization reconstruction (ROR) method is proposed for the retrace error calibration as well as the aspheric figure error extraction based on system modeling. An optimization function is set up with system model, in which the wavefront data from experiment is inserted as the optimization objective while the figure error under test in the model as the optimization variable. The optimization is executed by the reverse ray tracing in the system model until the test wavefront in the model is consistent with the one in experiment. At this point, the surface figure error in the model is considered to be consistent with the one in experiment. With the Zernike fitting, the aspheric surface figure error is then reconstructed in the form of Zernike polynomials. Numerical simulations verifying the high accuracy of the ROR method are presented with error considerations. A set of experiments are carried out to demonstrate the validity and repeatability of ROR method. Compared with the results of Zygo interferometer (null test), the measurement error by the ROR method achieves better than 1/10λ.

In this proceedings, we present a 3DoF (one linear, two angular) optical probe for measuring freeform optics in conjunction with an optical coordinate measuring machine (OCMM). This probe uses homodyne interferometry in a Michelson configuration and position sensing detection to simultaneously measure displacement, tip, and tilt. The goal of this work is to investigate point-to-point methods for measuring freeform optics and establish a probing methodology that can perform self-alignment with respect to the local optical surface. We present the design and preliminary benchtop validation of the probe's performance. Benchtop validation shows successful measurements with 5 nm linear and 20 μrad angular noise levels, with a 15 μm spot size. A CMOS sensor is used for visual confirmation of proper focus on measurement surface to minimize initial defocus error. A PSD detects linear horizontal and vertical displacement of the reflected beam from the measurement surface using autocollimation. In-phase and quadrature signals are measured by two photodetectors and post-processed to obtain displacement information. Periodic error caused by polarization effects and beam mixing is compensated by FPGA-based signal processing.

A wavefront retrieval method for the quadriwave lateral shearing interferogram obtained by randomly encoded hybrid grating (REHG) is proposed. The REHG consists of a binary amplitude grating and a phase chessboard, and the Faunhofer diffractions of this grating only contain the ±1 orders in two orthogonal directions. As a result, no order selection mask is ever needed by the REHG for quadriwave lateral shearing interference. To retrieve the phase distributions from the REHG interferograms, fast Fourier transform (FFT) technique is employed at first to get the frequency spectrum. By performing inverse fast Fourier transform (IFFT) of the +1 order spectrum in the x and y directions, it is possible to extract shearing wavefronts from the interferogram in both two orthogonal directions. Using the translation property of Fourier transform, the relationship between the Fourier spectrum of the shearing wavefronts and the Fourier spectrum of the wavefront under test is deduced. The wavefront under test is retrieved by establishing an evaluation function firstly and finding the minimum value with least-square-solution. Analysis and compensations are made to reduce the errors in the testing results. Simulation experiments have shown that this method can retrieve different phase distributions without losing high-frequency information.

We present a method of aspheric surface reconstruction from the curvature data along two orthogonal directions. The curvature is an intrinsic property of the artifact, which does not depend on the positioning error of a measuring sensor. In this paper, we showed that the curvature method is suitable for aspheric surface reconstruction along one direction and expanded this algorithm to two directions. Computer simulations were undertaken to explore the possibility of three-dimensional surface reconstruction. The simulation results and the position error diagnosis showed that the curvature method is robust against various positioning errors.

ULTEM® polyetherimide (PEI) resins have been used in opto-electronic markets since the optical properties of these materials enable the design of critical components under tight tolerances. PEI resins are the material of choice for injection molded integrated lens applications due to good dimensional stability, near infrared (IR) optical transparency, low moisture uptake and high heat performance. In most applications, parts must be produced consistently with minimal deviations to insure compatibility throughout the lifetime of the part. With the large number of lenses needed for this market, injection molding has been optimized to maximize the production rate. These optimized parameters for high throughput may or may not translate to an optimized optical performance.
In this paper, we evaluate and optimize PEI injection molding processes with a focus on optical property performance. A commonly used commercial grade was studied to determine factors and conditions which contribute to optical transparency, color, and birefringence. Melt temperature, mold temperature, injection speed and cycle time were varied to develop optimization trials and evaluate optical properties. These parameters could be optimized to reduce in-plane birefringence from 0.0148 to 0.0006 in this study. In addition, we have studied an optically smooth, sub-10nm roughness mold to re-evaluate material properties with minimal influence from mold quality and further refine resin and process effects for the best optical performance.

The Laser Displacement Sensor is designed according to the principle of laser triangulation. It is a precise geometric measurement sensor, and it is characterized by non-contact and high measuring efficiency. However, the measurement accuracy of the LDS is easily influenced by other factors, especially for free-form surfaces where the incidence angle has greater impact on measurement accuracy and the research is relatively less. The paper proposes a new error compensation strategy and the method of calculating incidence angle. It can effectively improve the measurement accuracy of free-form surfaces by inclination error compensation. The experiment verifies the correctness and reliability of the error model by using a Laser Interferometer. The result shows that the measurement accuracy is less than 10μm.

Different size polishing powder and different pH value ceria slurries were used to polish fused silica glass､K9 glass and Nd-doped glass on pitch plate. Material removal rates (MRR) of glass polished with different size powder and various pH value slurries, and textures of each sample were characterized. The results show that powder size has an effect on glass polishing performance: scratch densities increase with the increase of polishing powder size; surface textures become rougher with the increase of the size of polishing powder. The slurry pH value also affects glass polishing performance: MRR of fused silica glass are lowest under any pH value slurry while Nd-doped glass has the largest MRR; removal rates of all three kinds of glass will rise under both acidic and alkaline condition. Near neutral polishing environment and smaller size powder are useful for the surface polishing process. The results further reveal polishing mechanism and provide the guidance for glass surface process.

Dynamic Mechanical Analysis (DMA) and Bending Beam Rheometer (BBR) are applied to detect the property of the polishing pitch and get the creep compliance combining the craftwork of polishing. The simulation of workpieces’ surface in polishing is completed based on the Preston formula, Boltzmann superposition principle and Boltzmann superposition principle. A V-curve is gotten on studying the PV’s time history of the polished workpiece. Meanwhile, a confirmatory experiment whose parameter is agree with the simulation is completed, which the optimum result of PV, 0.3λ (λ=623.8nm) is similar with the optimum result of PV by simulation, 0.27 λ. A resemble simulated surface is gotten on the same PV with the experiment.