This PDF file contains the front matter associated with SPIE Proceedings Volume 11175, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

As U.S. manufacturing works to overcome a technical skills gap, apprenticeship is gaining favor as a post-secondary educational path. Registered apprenticeship is a structured program that requires on the job training of an employee, accompanied by related instruction, and a progressive wage scale as the apprentice progresses through the program. This presentation describes how the Occupation Title for a Precision Optics Manufacturing Technician was defined for the industry, and approved by the US Department of Labor (USDOL). The occupation was later deemed apprenticeable by the DOL, and the apprenticeship was designed and registered with NY State. The program entails a three year (6,000 hour) rotation through every department of an optics manufacturing firm, with defined outcomes regarding hours of experience and competencies gained. In this program, structured, hands on technical training is combined with theoretical class room learning to develop highly skilled manufacturing technicians. This presentation will explain many of the details surrounding registered apprenticeship, including adjustments and results encountered during the first three years of the Optimax program.

Sub-Angstrom surfaces are frequently specified by customers requiring increased optical and energy efficiency, with most stringent requirements from applications in the UV and from certain high power laser systems. Much research has been performed to understand related surface dynamics, with considerable amounts of information published on precision finishing of optical glass. Many suppliers of low roughness surfaces rely on finishing methods that create subsurface damage through the aggressive removal of material. While the magnitude of this damage can be minimized through the use of progressively finer abrasives, detectable levels of latent structure are still evident. However, finishing processes that merely wipe clean the Beilby layer without disturbing the substrate produce nearly perfect surfaces with little to no subsurface damage. This has been the focus of development efforts at Edmund Optics. By careful management of process variables, extremely smooth surfaces lacking subsurface damage have been demonstrated in fused silica and N-BK7 materials. Applications for optics having these characteristics are found in automotive, defense, medical, and industrial domains. This paper discusses results achieved for producing sub-Angstrom surfaces on fused silica and N-BK7 glass. Surfaces with measured roughness of 0.5Å have consistently been demonstrated on fused silica, with results of around 0.8Å shown for N-BK7. Types of processes useful for achieving these results will be discussed, along with basic metrology methods for producing reliable sub-Angstrom measurements.

In this work, we propose a method to discriminate between upper and lower side material removal during double side polishing of fused silica parts. It consists in engraving cone-shaped craters on the two sides, then measuring the profile of each crater before/after a polishing run. The comparison of the profiles leads to the thickness removed on each side during the run. The craters have been engraved using a CO₂ laser and their profiles measured thanks to a nano-scratcher. We have evaluated that this method can determine material removal with an accuracy of about 1μm, is insensitive to a part repositioning error under the tip of about 35μm, and has a repeatability of 0.5μm. Finally, we have been able to measure effective removal differences of 2μm between the two sides.

We investigate three-dimensionally configured (shaped) polishing pad materials in CNC polishing and introduce a cost of ownership model representative of a typical manufacturing process. Several different types of polyurethane polishing pad materials possessing different material properties and configurations were studied. Their utility as polishing tools was evaluated in terms of the finished part specifications and part-to-part consistency. Data shows the use of IC Optic Puck material with a grooved configuration provides optimum performance and consistency for CNC polishing processes. Furthermore, we extend the investigation and provide a cost-of-ownership model that can be used to estimate the benefit of such a tool platform for an optic manufacturing process.

We present a new experimental method for measuring subsurface damage (SSD) on ground surfaces of single crystal germanium and borosilicate glass BK-7 based on the morphology and mechanical properties dependence on depth into the material. The material selection allows us to compare crystalline and non-crystalline materials. We use spots of different penetration depths on ground surfaces by Magnetorheological Finishing (MRF) spots to remove part or all of the damaged layer, and then evaluate the surface roughness, fracture toughness and material removal rate (MRR) of MRF at the deepest point penetration of MRF fluid into the spot. The dependence of these results on penetration depth into the material reveals the subsurface damage of the surfaces. It is shown that the subsurface damage depths revealed by each property (surface roughness, MRR, fracture toughness) match each other.

Chemical mechanical polishing (CMP) is the most important process for global planarization. The micro material removal and planarization of the optical surface is a complicated process, and the surface shape of optics is effected by kinematics, pressure, and chemical conditions. Moreover, it is a remarkable fact that the distribution characterization of polishing particles also has an important effect on material removal uniformity, especially for leather pad and Tin polishing lap. Large optics were always polished to a convex shape for the low density of valid abrasives in optic center. The porosity and grooves distribution of pad plays a major role in slurry delivering. The novel model of contact and material removal is presented in which pad characterization, and polishing particles delivery and distribution effects are included. With the modified pad asperity and optimized grooves, the particles have been inclined towards well-distributed, and experiments validated that the optic figure is significantly promoted.

Optimax Systems Inc. improved reliability of legacy asphere polishing platforms, preserving niche capabilities at a demonstrated level. In asphere manufacturing, key tools have evolved over the years. While not as capable, older technology is able to create useful surfaces, and, for some geometries, still represented the best option. Select work waited for older machines being repaired over and over. We set out to find a modernized version of these polishing platforms. We found we could not only match the results of the 20+ year old technology, but also surpass its functionality.

The lack of trained machine operators is a significant challenge in modern optical fabrication facilities. The request for machine automation is growing through the entire range of production. This starts in the range of micro optical components for the use in life science applications, such as endoscopes and microscopes, as well as in larger applications such as sports optics (binoculars, scopes etc.) and even larger optics. While large optics is a challenge by itself, the drive for automation currently can be seen more on the smaller end of the optical fabrication range. This paper introduces a solution for fully automated production of optical components, especially for diamond pellet lapping and for polishing. The concept includes the innovative HydroSpeed Polishing Technology. Also aspects of process supervision and process control are considered. As a loading solution, the concept is based on a 6 axis robot, feeding pallets according to the DIN standard, as well as customised pallet solutions. The presentation includes videos and photographs of the fully automated solution, but it is important to note, that the concept can be scaled down for more simplified solutions, using less complex loading technology and still produces optics autonomous.

Ultra precision diamond machining is a well known technology for the manufacturing of optical components made of non ferrous, plastic and crystalline IR materials. The application of this process to ferrous materials is enabled through the ultrasonic assisted machining process, which has established its position in the market over the last years. Diamond machining of glass or even tungsten carbide is conventionally extremely limited. This presentation will discuss the possibilities that are given through the application of ultrasonic assistance to the conventional diamond cutting process on glass. The possibilities and the limits will be discussed.

Mass production of Ge lenses is a very common operation in the infrared (IR) optics manufacturing industry. The process of choice for production of such optics is single point diamond turning (SPDT). Ge is a very suitable material for SPDT and this gives the ability to produce complex elements with excellent surface finishes (<5 nm RMS). In this paper the application of the Micro-LAM (referred to μ-LAM hereafter) process in SPDT of single crystal Ge is reported. The main idea is to investigate the maximum in-feed rates for a spindle speed of 5000 RPM as function of the tool nose radius and rake angle. Typical industry practice is to machine Ge with a spindle speed of 5000 RPM to 12000 RPM, and finishing in-feed rates between 0.5 μm/rev and 1 μm/rev. It is shown that an increase in the tool nose radius leads to an increase in the maximum in-feed achievable without the appearance of brittle fracture zones on the surface. It is also shown that using larger negative rake angles can also enable higher tool in-feeds without trade-off’s to the surface quality.

In this paper, experimental results on single point diamond turning (SPDT) of fused silica glass, using the µ- LAM process is reported. It is shown that with a certain combination of tooling geometry, coolant, and laser beam power, surfaces with roughness values of 20 nm - 30 nm RMS can be achieved. Such surfaces are obtained with spindle speeds of 1000 RPM. All the experiments are done on planar samples. For tool machining track lengths greater than 3 km, a tool wear-land of 10 µm on the flank face of the tool was observed.

Flat glass finishing has traditionally been performed in batch processes that apply constant loads in double sided lapping and polishing operations. This paper simulates the constant rate grinding of glass that might be used in high volume applications where a more continuous process approach, such as double disk grinding (DDG), might be advantageous. The dynamics of grinding glass can be demonstrated uniquely and simply through the use of an analysis method first described by Lindsay and Hahn1 for bonded wheels. Measuring the normal and tangential forces during constant rate removal processes allows one to calculate the volumetric material removal parameter and the specific power, as well as threshold forces and specific energy. Performance comparisons between Trizact™ Diamond Tile (TDT) abrasive grade, glass type, lubricant type & concentration, and the TDT diamond abrasive concentration can be effectively compared to identify improved removal performance for a given type of glass. Such an analysis can potentially help improve constant rate glass grinding operations.

The publication describes the application of subaperture correction technologies for the fabrication of high-end aspheres and freeforms. In addition to the established processes grinding and polishing, technologies such as diamond turning and smoothing polishing to reduce mid-spatial frequency errors will be examined. The presentation focuses on the technology chain necessary for the production of high-precision aspherical components. The final correction of surface errors of optical components with the help of subaperture finishing tools MRF (magneto-rheological finishing) and IBF (ion beam finishing) will be described. Besides the increased demands on machining processes the accuracy of measuring procedures is becoming more and more important. “Pixel-precise” measuring is the basis for realization of higher demands. The impact of alignment errors (coma, spherical aberration, twist) on form accuracy is discussed. Results will be presented taken from the manufacturing of two strong aspheres.

An OptiPro UltraForm Finisher 300 (UFF) was used to produce removal spots on Fused Silica ground surfaces. The goal of this research was to assess the relationship between Belt Compression (μm) and Material Removal Rate (mm3/min) for compressions ranging from 2 to 100 μm. With this data the validity of the Preston Equation for these small compressions was also assessed. The data displays trends for the dependence on compression of Material Removal Rate (MRR), and spot dimensions—Spot Depth, Spot Length, and Spot Width. Compressions ranging from 2 to 25 μm require further investigation to establish clearer correlations.

Continuous phase plate (CPP) is the vital diffractive optical element in large laser devices. It is extremely difficult to manufacture owing to its random and small feature structures. Bonnet polishing (BP) has obvious advantage of high efficiency, and has great potential in high-efficient manufacturing of large optics. In the paper, BP techniques have been developed to manufacture CPP. Firstly, the relationship between the process parameters and tool influence functions (TIFs) has been analyzed, and the adjustable ranges of TIF size and efficiency have been determined. Then, a surface topography simulation model for the forecast of CPP residual errors has been established. Based on the model, the influence of TIF size on the accuracy of CPP has been simulated and analysed, meanwhile the optimized TIF has been determined. Finally, an experiment has been carried out by a 300mm×300mm CPP element. The result has shown that the residual root-mean-square (RMS) of CPP is 26 nm. Based on the optimized TIF of BP, it has been realized the high-efficient and high-precision processing of CPP in this paper, and a new technical reference for the CPP manufacturing has been provided simultaneously.

Within the modern production of high-precision optics, Ion Beam Figuring (IBF) is an established machining process. IBF uses an ion beam with a Gaussian particle distribution. Atoms are sputtered from the workpiece surface by accelerated ions. Compared to other correction methods (e.g. MRF) IBF provides a significantly smaller tool, enabling precise and deterministic results. The machining takes place contactless in vacuum. Thus the technology qualifies for many unique application possibilities in the production of high performance optics. After a brief introduction to the basics of IBFtechnology, this article features various industrial applications: The nanometer accurate correction of optical surfaces, the correction of angular errors as well as smoothing, structuring and decoating of lenses will be presented. Focus of the lecture is the improvement of wavefronts in optical systems using IBF-processed correction surfaces. The complete process is presented and illustrated with examples and results.

Dwell time calculation is one of the most important process in a highly deterministic computer-controlled Ion Beam Figuring (IBF) process. It is modeled as a deconvolution process between the desired removal map and the beam removal function, which is an ill-posed inverse problem. A good dwell time solution should fulfill four requirements: 1) it must be non-negative; 2) it should closely duplicate the shape of the desired removal map; 3) the total dwell time is expected to be as short as possible; 4) the calculation time is reasonable. Dwell time algorithms, such as Fourier transform-based algorithm, matrix-based algorithm, and Bayesian-based algorithm, have been proposed and applied to IBF. However, their performances were never clearly examined and described accordingly. In this research, we provide a quantitative study on the performances of these dwell time algorithms based on the aforementioned four requirements.

As the demand for higher precision optics grows, commercially available manufacturing options are needed to meet the stringent requirements requested by optical designers. Short radius concave optics have been a challenge for optical manufacturers as sub-aperture polishing tools that are small enough to accommodate the shape of the optic have not been available. Until recently, the smallest MRF wheel was 20 mm in diameter, which allowed polishing a minimum concave radius of approximately 14 mm. With the newly developed 10 mm diameter MRF wheel, we can push the previous MRF boundaries to accommodate even shorter concave radii. Not only does this tool extend the concave radius limits of MRF technology, but it also improves the efficiency of correcting mid-spatial frequency errors. As the removal function, or ‘spot’, becomes smaller we can make corrections to errors with higher spatial frequencies. In addition, the geometry of the wheel and the size of the removal function provide further benefits that will be explained. This module was designed to be compatible with any machine within QED Technologies’ Q-flex family of MRF equipment.

The determinism of the MRF optical polishing process relies on a well-characterized and stable removal rate during polishing runs. The workpiece immersion depth into the MR fluid is a main contributor to the removal rate. During polishing, the CNC machine platform attempts to maintain a consistent immersion depth throughout the toolpath to keep the removal rate constant. Polishing aspheric parts with either significant wedge or unaccounted for aspheric shape can result in unpredicted removal rate errors due to a change in plunge depth. By accounting for the figure error expected from the change in plunge depth in the hitmap, the removal error resulting from high amounts of wedge and aspheric departure can be mitigated. This process allows MRF to figure correct highly wedged parts and to reduce MRF iterations on challenging aspheric parts.

The production of high-precision aspheres typically involves at least one extensive chemo-mechanical polishing process to remove subsurface damage after grinding. Especially when machining glasses that are prone to fracture from grinding, subsurface damage can be substantial. As a result, subsequent polishing times are high and it is challenging to maintain a reasonably low surface form error. In order to reduce processing times and increase process stability SwissOptic established an ultra-precision grinding process. This process operates in a ductile grinding mode that not only minimizes subsurface damage but also leads to surfaces with form errors well below one micrometer. The high surface quality after grinding makes it possible to omit chemo-mechanical polishing processes. Instead, we polish and form correct the ultraprecision ground aspherical surfaces in a single process step by applying magnetorheological finishing (MRF). In this paper, we demonstrate the feasibility of this approach based on the production of a fused silica asphere and a steep S-PHM52 asphere. We utilize QEDs Q-Flex 300 for MRF polishing. Very aggressive process parameters are used to keep processing times as low as possible. We find that polishing and form correction to an irregularity below 300 nm is feasible in less than 30 minutes. Depending on the desired quality of the aspheres, MRF polishing parameters can be adjusted.

For over 20 years, QED Technologies has been expanding the size and functionality of its MRF precision polishing product line. We have recently refreshed our meter-class platforms, developed a custom MRF upgrade for a customer’s existing 3-meter platform, and have begun development on a new half-meter platform. With the demand for new land, air and space-based imaging systems increasing, there is a growing need for optics with diameters larger than 8-12" (200- 300 mm). Our latest QED.NET software, pad polishing, multi-part batch polishing and our electronic fluid measuring system are just some of the new or updated capabilities integrated in our latest large-format MRF platforms. We refreshed the Q22-750P2 platform, which is optimized for plano polishing with two fixed MRF heads for fast changeover between wheel sizes. We expanded the capability of our Q22-950F polishing center, and now offer the Q22-1200 in its place. This platform can be ordered in four different configurations to meet a wide range of capability and price points. We have begun the development of the Q22-600 – a platform to fill the gap between the Q22-1200 and our Q-flex 300. In this paper we will review and contrast the capabilities of these new large-format platforms and present results to illustrate these capabilities.

Temperature changes can detrimentally affect an optic’s performance due to changes in radius of curvature, thickness, and index of refraction. This is a particularly tricky problem when combinations of these changes produce a decrease in focus with increasing temperature such as infrared systems. Current solutions include active focusing mechanisms and nesting tubes of different materials that cancel each other’s thermal expansion, but these solutions add size and mass. ALLVAR alloys are the only metals that shrink when heated and expand when cooled, known as negative thermal expansion (NTE), making them a unique solution to this thermal focus shift problem. They can exhibit NTE down to -30 ppm/K. This unique property opens the opto-mechanical design window for athermalized optics with decreased size and weight. This presentation will discuss the optic design potential of ALLVAR alloys and exhibit the first optic demonstration of ALLVAR in a visible and infrared optic assembly.

This talk will address the ideas of intelligent material design when applied to infrared-transparent glasses. By using literature data as a jumping-off point, glass properties can be reduced to mathematical equations whose simultaneous solution results in a material with specifically targeted optical properties such as index and dispersion, as well as targeted mechanical properties such as glass transition temperature and coefficient of thermal expansion. Using this design approach eliminates the need for the scattershot trial-and-error method by which novel chalcogenide glass compositions are currently designed. Examples relevant to current infrared optical systems and their SWaP reduction will be discussed.

In this work, we are aiming to reduce the mass of large precision mirrors for space missions by using space approved composite materials. We report the development of an active/adaptive optics prototype of carbon fiber reinforced polymer mirrors using a pre-impregnated (pre-preg) composite MTM44-1/IMS65. The carbon fiber mirror has 16 layers of carbon fiber and one layer of polishable resin which compensate the well-known problem of ‘’fiber print through’’. The development of a fabrication method, suited for creating a CFRP mirror is outlined. As all materials will change properties to some degree, during cool down to cryogenic temperatures, FEA model is employed to investigate the change on overall form and figure of the mirror. Characterizing this dimensional change is critical in insuring that any mirror material can be used in this environment and, if required, corrected either by utilizing a deformable mirror control systems or by correction in the optical system. Two different piezoelectric actuators are modelled and used to create an active composite reflector. Push actuators and micro fiber composite (MFC) actuators are simulated and the performance of them are compared by surface deformation and dynamic response.

Additive manufacturing has taken many industries by storm, bringing a revolution to prototyping and manufacturing lines. For the most part, Glass and Optical Materials have been left on the wayside during this insurgence of additive manufacturing. Initially, the processes had very significant barriers to create practical uses for glass and optical materials. The emergence of UV curing or crosslinking polymers from a bath has proven useful for some optical elements and component applications for organic polymers. The majority of inorganic glasses are already fully cross-linked and cannot be used in curing/crosslinking methods. Rochester Precision Optics (RPO) is constantly developing and designing optical elements and assemblies, having a cheap and quick process to prototype optics for demonstrators and initial prototype systems would be extremely valuable. RPO has investigated a number of methods to incorporate additive manufacturing of glasses into the optics and photonics fields. Laser based approaches of additive manufacturing of chalcogenide glasses will be presented. Optical properties and performance is compared across various additive manufacturing approaches and compared against bulk traditional material and processes.

Fizeau interferometry is a flexible tool for optical surface metrology. Different transmission spheres (TSs) enable testing most spherical surfaces, and selecting a TS to measure form irregularity of a given surface is straightforward. New applications, however, have increased the variety of surfaces to test beyond spheres. Aspheres and freeforms are particularly challenging, as interferometers only resolve small deviations from a sphere without additional corrective optics. Furthermore, the surface irregularity specification may be accompanied by tolerances related to mid-spatial frequencies (MSFs), such as power-spectral density (PSD) or local slope. These MSF specifications may require spatial resolution beyond what a typical full aperture test provides. Subaperture stitching interferometry is particularly well-suited to measuring MSFs, and can also significantly increase non-null aspheric and freeform measurement capability. Selecting the most appropriate TS for a given surface, however, becomes more complicated. We explore how the surface specification interacts with the interferometer’s slope capture limit to determine an “optimal magnification” for that surface. We show how to select the most appropriate TS for the surface, given the optimal magnification and other interferometer constraints (e.g. cavity length, focusing range). We demonstrate this TS selection process for a toroid measurement (with 400 micrometers departure from best-fit sphere). We conclude with guidance for designing aspheres and freeforms that can be measured more easily with stitching interferometry.

Regarding the progress of optical design in favor of freeform surfaces, it becomes necessary to scale their feasibility with appropriate criteria in order to get a standard between an optical designer and an optical manufacturer. Two criteria are necessary, one linked to polishing process and one appropriate for measurement limitation. First criterion can be the extension to freeform surfaces (defined here by first Zernike terms) of a previous criterion which was calculated using conical equation. This criterion is representative of surface’s curvatures fluctuations which limit polishing efficiency and can generate high frequency defects. The second criterion should take into account the difficulty to measure the surface as feasibility needs also good knowledge of the correction polishing cycle to be performed. Different solutions exist for an accurate measurement in the range of nm. As demonstrated in the article, slopes versus reference surface is the limiting factor for a majority of measurement solutions. Therefore the criterion will be linked to a slope parameter. The governing principle of these criteria is to remain close to some relevant physical dimensions. In this idea, the polishing feasibility criterion defined in this paper will be comparable to tool diameter of Computer Controlled Polishing which refers to equipment resolution of optical manufacturers. In the same idea, we project to define a dimensioned criterion for measuring feasibility which can be compared to engraving resolution for a given Computer Generated Hologram.

As freeform and conformal optics are becoming more broadly used in the optics industry, the manufacturing technology and processing conventions need to be developed to meet the requirements and challenges posed in the manufacturing of these parts. These optics reduce the number of total optics required in an assembly in addition to overcoming the limitations in rotationally symmetric optics. While these optics offer many benefits for system capabilities, these traits also make manufacturing and metrology more difficult. In order to manufacture these complex optics, OptiPro has been focusing on development of the software, hardware, and processing techniques required to meet the stringent part tolerances. For software, OptiPro has been working on the continual development of PROSurf, a CAM package geared specifically toward freeform optics, and the UltraSurf software, which controls OptiPro’s non-contact metrology system. For hardware, the main area of focus has been on fixture development: how should the part be held so that it can be transferred between machines repeatably while still providing adequate support during processing and access to the alignment features. One of the focus areas of processing improvement has been on developing the conventions for the surface datums used for locating the surface and referencing analyzed data against. This paper will present the challenges in freeform manufacturing along with the solutions that we have developed to meet these manufacturing needs.

Conventional windows for airborne payloads are often discontinuous with the aircraft or pod skin. A protruding structure or hollow cavity increases aerodynamic drag, which consumes more fuel and thus reduces the amount of time available on-station. These geometries give rise to turbulent aero-optical effects, which can reduce the payload’s optical performance because it has to see through turbulence. This paper describes a multi-paned or segmented window concept that matches the local topology of the aircraft pod or skin. This approach is suitable for optical payloads having multiple fixed fields-of-view such as staring infrared search and track systems, but not scanning systems. This approach for creating a near-conformal window assembly should be particularly useful for rapid prototyping of windows for airborne optical payloads, providing a nearer-term alternative to monolithic windows that are ground and polished into complex shapes. In this paper, a 14-inch diameter pod faring with three window segments was chosen as a point design for a notional airborne optical payload. Fused silica planar windowpanes were fabricated with matching, mating mitered edges. The panes were chemically bonded directly to each other with a sodium-silicate solution. The bonding process and fixturing are described. The resulting glass bond is strong and minimizes the non-useable seam between panes. This approach increases the clear aperture of each pane compared with windowpanes bonded into individual mechanical bezels. Interferometric measurements of the prototype show no degradation in transmitted wavefront error after silicate bonding.

The manufacturing of optical components introduces varying surface errors with diverse impact to the optical performance. In this paper we propose a measurement technique to detect form and mid-spatial-frequency errors of specular freeform surfaces. Results from simulation and experimental measurements are presented. The aim of a manufacturer of optical components is to produce its products as precise as possible according to the given parameters of the designer. However, errors due to the manufacturing process are not avoidable. Regarding surface deviations, one distinguishes between form deviations, mid-spatial-frequency errors and roughness. The proposed measurement technique in this paper is able to detect form and mid-spatial-frequency errors in one measurement. Therefore, the investigated surface is scanned with a single laser beam. The direction if the reflected beam is measured using Experimental Ray Tracing. From the direction of the incident and the reflected beam, the surface gradient at the investigated position can be determined. Proper integration methods lead to the reconstruction of the surface. Knowing the model of the investigated optical components, the form deviations and the mid-spatial-frequency errors can be calculated. Considering the model as unknown, the mid-spatial frequency-errors can still be determined, by separating the mid-spatial-frequency components from the low-frequency form information of the reconstructed surface. In this paper we propose a measurement technique for the measurement of form and mid-spatial-frequency errors of specular freeform surfaces. The measurement principle as well as results from simulation and experimental measurements of freeform surfaces are shown and evaluated.

With optical technology and design advances, larger freeform optics are increasingly sought after by consumers for an expanding number of applications. Many techniques have been developed to meet the challenges of producing these nonrotationally symmetric optics, which cannot be fabricated via traditional manufacturing and metrology processes. In the past, methods were established to create smaller freeforms. With demands for more and larger freeforms, manufacturers must scale up existing processes. This paper will present some of the challenges and solutions of extending freeform polishing capabilities from approximately 150 mm diameter parts to a component of over 500 mm in diameter. In fabricating the 500 mm freeform, Optimax has addressed many of the manufacturing and metrology challenges using some proprietary techniques as well as some novel methods. Some of the approaches explored in this paper include acquisition of a substrate blank of sufficient dimensions, material handling logistics, polishing strategies, and metrology. Earlier freeform polishing projects at Optimax utilized a smaller pick-and-place style, 6-axis robotic arm. The route to design, build, and program a scaled-up polishing robotic arm is discussed. Considerations for polishing path planning and metrology are explained. In addition, deflectometry, a non-interferometric measurement method using fringe reflection and ray tracing, has been developed in parallel to help measure mid-spatial frequency error on a part surface faster and more safely than traditional methods, as it can be done in-situ.

Freeform optical components are becoming more prevalent in the precision optics industry. Metrology of freeform surfaces is traditionally limited to coordinate measuring machines, or computer-generated holograms. OptiPro has developed UltraSurf, a non-contact metrology platform that has been adapted to measuring freeform surfaces. The non-contact probing method, and multiple axes of motion allow UltraSurf to scan freeform optical surfaces and the associated datum structures. Datum structures define a coordinate system that all the freeform surfaces of a component can be referenced for metrology and manufacturing. Iterative corrective grinding and polishing is dependent on accurately locating the form error map to the surface within the machine. Measuring the datums along with the surface provides an absolute reference for the form error map. Allowing an operator to correct form error with confidence that the machine will grind or polish in the correct location. Datum and optical surface metrology together will allow referencing multiple freeform surfaces to each other, which is critical on transmissive freeform systems. Practical examples of non-contact freeform metrology with the UltraSurf will be presented along with considerations of datum features.

A new interferometer has been developed using an engineered low coherence LED illumination system, where both the spectral and spatial coherence are tailored to allow single surface interference from plane parallel transparent optical components such as optical windows, glass wafers, glass computer disk substrates, etc. without the need to paint the rear surface to suppress interference from that surface. Only the reflection from a surface at a specific optical path difference can interfere with the reference beam eliminating spurious interference. While the interference region due to spectral coherence is engineered to provide interference within a 280 micron zone, diffraction at surface defects and dust within this zone produces secondary wavefronts which can interfere with the test and reference wavefronts, producing phase artifacts which can limit measurement accuracy in standard coherent laser-based interferometers; these phase errors are eliminated by using a spatially extended LED source. For this low coherence interferometer, the “purity” of interference between the test surface and a high quality calibrated reference surface, along with high spatial resolution phase measurements, offers the ability to review waviness and surface polish variations to sub-nanometer height resolutions over a large 4 inch field-of-view. Examples of polish process variations of optical components, along with power spectral density plots (PSD) are shown where the data were acquired with OptoFlat, a downward-looking LED-based low coherence interferometer newly developed for the rapid measurement of precision polished flat surfaces including thin transparent optical components without special surface preparation.

Spectrally controlled interferometry promises to increase accuracy at a reduced cost for radius of curvature measurements for spherical optics by removing the catseye position during measurement and exploiting the inherent ability to measure absolute distances without mechanical compensation.

We present an optical metrology instrument for measuring both transmitted and reflected wavefront error (TWE and RWE) of coated or uncoated optics over a diameter of 4 inches in the SWIR range. Depending on the coating transmittance and reflectance, the measurements were done at different wavelengths from 1100 nm to 1650 nm. Fizeau interferometry is a standard technique to measure the TWE and RWE of uncoated optics. But in the case of coated optics (bandpass filters for example) measurement of TWE is not possible because the optics may not transmit the interferometer laser light. Moreover, for measurements at different wavelengths, a dedicated interferometer has to be built for each different wavelength. The chosen solution is based on a quadriwave lateral shearing interferometer (QWLSI) wavefront sensor. QWLSI is an achromatic technique, meaning that it measures optical path differences at any wavelength without any need for recalibration at specific wavelengths. Consequently, various sources at different wavelengths can be used with the same instrument and metrology bench. In addition, QWLSI measures the derivative of phase contrary to interferometer that measures phase. Therefore, QWLSI has by design a better WFE dynamic range for TWE and RWE measurement. Moreover, an achieved accuracy below 30 nm RMS is perfectly adapted to optical metrology measurement. The optical solution is a standard double pass configuration composed of a collimator and a beam expander to adapt the size of the beam to the aperture of the SWIR wavefront sensor. Different sources between 1100 nm and 1650 nm were integrated.

High efficiency surfaces for low loss or high-power laser applications require extremely sensitive instrumentation to measure. Because these sub-angstrom surfaces push the limits of current optical profilers and atomic force microscopes great care must be taken to ensure the accuracy of surface roughness measurements. This paper will explain the techniques required to optimize the performance of the optical profiler and, most importantly, will explain the absolute necessity of understanding the spatial frequency bandwidth which creates the roughness value. It will be shown that this bandwidth defines instrument capabilities and facilitates data correlation between vastly different metrology instrumentation.

Non-destructive and non-contact centering error measurement of optical surfaces in fully mounted optical systems can provide valuable insights into the optical and underlying mechanical properties of lens systems. Commercially available solutions measure this centration by detecting the angle at which incoming light is reflected from each optical surface. Advanced algorithms are then used to calculate the tilt and lateral offset of all optical elements with arcsecond and submicron accuracy. These centering error measuring systems generally use an axis of rotation as reference for each measurement. While this enables cost-efficient systems, it limits the principle to vertical designs and requires both linear and rotational movements for each surface, resulting in long overall process times. In our article, we introduce a new measuring system that uses a high-precision linear axis for the centering error measurement. The omission of the axis of rotation leads to a significant reduction of the measuring time. With our approach, the centering error measurement of a single optical surface can be performed on a single image. As the measuring head focus is shifted, the linear stage itself becomes the reference axis. Using special calibration techniques, we can ensure that the precision of the measurement results is similar to that of a conventional rotation axis system. The measuring method is ideal for optical assemblies whose position and orientation may not be changed during measurement, such as samples whose optical axis must always be aligned horizontally (e.g., those with floating lens elements), or workpieces that run through the production in large numbers in mass production on a tray together. This approach is also well-suited for samples that are tightly integrated into large and inflexible systems. In addition to the presentation of the principle of measurement, results of measurements of a complex objective are presented in direct comparison to the conventional measuring technique.

As optical designs require increasingly more aspheric elements to achieve high-resolution, high-quality imaging from smaller, more cost-effective systems, active alignment solutions to center and de-tilt aspheres in-situ during assembly are becoming paramount. Traditional active alignment systems, i.e. autocollimators, determine lens orientation from center of curvature (CC) positions of each surface and are consequently limited when measuring aspheres. Such tools measure the paraxial CC; therefore, measurement is inherently blind to orientation of the aspheric edge, leading to centered yet tilted aspheric surfaces and, thus, degraded image quality from the final optical assembly. Current market solutions to measure aspheric tilt consist of external probes directly measuring the aspheric edge; however, this approach involves addition and alignment of multiple precision stages and secondary sensors, adding to the complexity and cost of alignment systems. This paper demonstrates a novel solution for accurately measuring aspheric tilt during the assembly process utilizing the existing capabilities of the Lens Alignment Station (LAS). The LAS is an active alignment tool whose specialized design extends measurement ability beyond the requirement of confocal reflection. Aspheric measurement begins with standard vertex centration using the LAS at confocal position, but for tilt, we image away from confocal position and flood the surface with a high NA objective sampling the aspheric edge. Beyond confocal reflection, the LAS detects retroreflected concentric fringes that trace an orbit as a tilted asphere rotates. The orbit radius is proportional to tilt magnitude, such that simple software calculations accurately yield aspheric tilt measurements without requiring expensive external hardware.

Optical designs have traditionally been designed around an axis of symmetry to which the actual components must conform within specified tolerances. Until recently and with few exceptions, it has been sufficient for the drawings of the several elements to call out local surface tilt tolerances at the physical centers of each element (or between two plane faces.) DIN 3140 and ISO 10110-6 (1996) created a formal framework for specifying surface tilt. While surface tilt may have been the specification, it wasn’t always a convenient method of measurement in the shop: Edge thickness variation, beam deviation, or axis decenter are sometimes better fits to the production and QA capabilities or optomechanical requirements. In the U.S., subsets of ASME Y14.5M1 were combined with text drawing notes allowing both greater flexibility and frequent and occasionally expensive misunderstandings. With modern optical manufacturing and design techniques allowing widespread utilization of rotationally invariant aspheres, torics and biconics, and freeform optics – many with non-circular edges – the terms “centration” and “tilt” are no longer adequate to specify the geometric relationships between one or more surfaces and their mechanical boundaries and constraints. In response, ISO 10110-6 (2015) has been greatly expanded to meet the needs of an advancing industry – and to support measurement methods more directly associated with optomechanical requirements and shop capabilities. This article is a tutorial to aid in understanding and using this essential document.

The wish for smaller and lighter telescopes, better image quality, and shorter wavelength applications sets ever increasing demands towards the quality of optical surfaces. In metal mirror fabrication with diamond turning, mid spatial frequency errors become the most limiting factor in achieving a certain surface quality, and reducing them puts high requirements on the manufacturing. A first step in improving the surface quality is to utilize appropriate analysis methods that account for the highly anisotropic surfaces developing at diamond turning. In this article, a novel, two-dimensional representation of the power spectral density is demonstrated, which takes up the many benefits of the established PSD and extends it to meet the demands of anisotropic surfaces.

Full-field deflectometry, which combines high-precision and robustness to external perturbations, is well adapted for the characterization of high-precision freeform mirrors. Instead of measuring the surface height map like interferometry does, the instrument will estimate the surface slopes in two perpendicular directions. The principle of the method is to measure the angular distribution by applying spatial filtering in the Fourier plane of the mirror under test. This method has been called phase-shifting Schlieren deflectometry Inspection of mirrors in terms of slopes instead surface height offers multiple advantages. In particular, deflectometry is well adapted for the detection of waviness, which is a mid-spatial frequency topography error. Waviness detection during the diamond turning process is critical since it is hard to remove afterwards by polishing. Keeping the mirror mounted in the lathe during the measurement of its shape will simplify the process since it will avoid misalignment when re-mounting the mirror in the lathe. The presentation will discuss the principles of phase-shifting Schlieren deflectometry, the performance specification based on the tolerance study of the four-mirror spectrometer, the design of the new instrument under development and finally preliminary measurements of freeform mirrors performed at AMOS with the mirror mounted in the lathe that demonstrate the capability of the instrument for the detection of mid-spatial frequency errors.

We present an optical metrology instrument for measuring the transmitted wavefront error (TWE) of coated or uncoated optics having large aberrations. Fizeau interferometry is a standard technique to measure TWE. However, the dynamic range is limited and measuring large aberrations requires the use of computer-generated holograms or null lenses, which increases both cost and time dedicated to precise alignment. The chosen solution is based on a quadriwave lateral shearing interferometer (QWLSI) wavefront sensor. QWLSI is an achromatic technique, meaning that it measures optical path differences at any wavelength without any need for recalibration at specific wavelengths. Moreover, QWLSI directly measures phase derivatives unlike Fizeau interferometers that measure phase. Therefore, QWLSI has, by design, a better wavefront error dynamic range for TWE and also reflected wavefront error measurements. The proposed optical solution was characterized using samples previously measured using an interferometer from Zygo. Comparisons were made on samples having 5 µm defocus P-V and 3 µm astigmatism. Finally, measurements were made on optics presenting more than 20 µm peak-to-valley (P-V) of defocus aberration. Measuring this sample with a classical interferometer is not possible and our solution provided TWE measurements without using any relay optics.

Freeform optical elements are applied in various fields. In special purpose, ultraprecise aspherical mirrors are necessary for developing third-generation synchrotron radiation and X-ray free electron laser (XFEL) sources. In addition, the optical system of extreme-ultraviolet lithography (EUVL) is composed largely of high-accuracy asymmetric mirrors. The 3D profile measurement with nanometer resolution is essential to produce ultraprecise mirrors. Accordingly, the demand of a 3D profiler with nanometer resolution is increasing. We have developed a nanoprofiler which traces the normal vector of the mirror surface. This measuring method is based on the straightness of laser light and accuracy of rotational goniometer. This machine consists of four rotational stages, one translational stage and optical head which has the quadrant photodiode (QPD) and LASER head at optically equal position. In this measurement method, we conform the incident light beam to reflect the beam by controlling five stages and determine the normal vectors and the coordinates of the surface from signal of goniometers, translational stage and QPD. We calculated the three-dimensional shape from the normal vector and the coordinate of each point by a reconstruction algorithm. We have measured shapes with various radii of curvature. In this report, we measured a figure error of concave spherical mirror with 50 mm radius of curvature. 50 mm is the smallest radius of curvature so far. Generally, the systematic error increases as the radius of curvature decreases. And we discuss show the measurement result of figure error and repeatability.

With the continued growth in demand for precision polymer optics across a broad range of industries, markets, and product applications, so too has the demand increased for highly performing optical coatings for these polymer lenses. Aside from rigorous optical specifications, coatings on polymers must also exhibit desirable mechanical properties that may include significant abrasion resistance, adherence, and environmental stability. Special surface characteristics such as hydrophobicity, oleophobicity, anti-static properties, and general ease of cleaning properties for the coating stack are highly desirable attributes. Satisloh is a global leader in the PVD equipment space for successfully processing optical coatings on precision polymer optics. Details will be shared on the unique Satisloh equipment attributes, ancillary equipment and technologies, coating process design considerations, and special optical coating layer attributes. The combination of these technical considerations is the basis for success in developing and processing premium quality thin-film coatings for precision polymer optical lenses. Attend this commercial paper presentation for more details on how Satisloh can assist your company to succeed with performance coatings for plastic optics.

Cholesteric glassy liquid crystal films (Ch-GLCs) are solid-state materials with unique optical properties derived from embedded supramolecular structure. Owing to their ability to be processed into thin films combined with their remarkable durability, Ch-GLCs are increasingly attractive for variety of optical operations including single element circular polarization, notch filtering, and polarized luminescence. Ch-GLCs are most frequently processed into monodomain thin films to exhibit a helical stack of in-plane chiral mesogens with orientation that varies periodically through the thickness of the film. Two distinct optical phenomena emerge from this kinetically frozen supramolecular order: (i) selective reflection and transmission of right and left handed circular polarized light owing to the periodic structure defined by the optical pitch-length and (ii) circular dichroism arising from light-absorbing chiral constituents. In our current experiments, we are modulating the spectral range of the stopband through thin film processing, and we are doping GLC films with absorbing dyes to achieve circular dichroism over different spectral ranges. Our objective is to understand the overlap between stop-band behavior and circular dichoism to enable polarization into the SWIR range as well as optical isolation of incident light. The effort is part of a new center, Advanced Materials for Powerful Lasers (AMPL), based at the University of Rochester.

We describe a novel dynamic spectroscopic ellipsometer and its advanced imaging spectro-ellipsometric scheme based on one-piece polarizing interferometric module. The proposed dynamic spectroscopic ellipsometer requires neither moving parts nor time dependent polarization modulation for extracting spectroscopic ellipsometric parameters. By employing a snapshot single spectral data, we reconstruct spatially resolved spectral ellipsometric information of ultrathin films coated on a freeform surface with high precision and accuracy. The dynamic measurement capability of the proposed imaging spectro-ellipsometer is demonstrated for large-scale periodic nano-patterns fabricated on roll surface.

HfO2 coatings are undoubtedly one of the most successful materials for high power laser applications. The ion beam assistance during the film growth is one of the most useful methods to obtain dense film along with improved optical and structural properties. As a consequence of the ever increasing application field of modern optical technologies, new demands for the optimization of deposition processes for high quality optical coatings with increased power handling capability, lower stress and optical uniformity are required for HfO2 film. In this paper, HfO2 films have been evaporated with ion assistance, provided by three different ion or plasma sources (APS, lion, RF). The influence of working gas flow (Ar and O2), ion energy and ion beam density on the HfO2 film properties was experimentally investigated. The film properties such as index of refraction, optical absorption and residual stress have been examined by spectrophotometry, laser calorimetry, and substrate curvature measurements. Microstructure have been studied by xray diffraction. Furthermore, a set of HfO2 monolayer were tested for LIDT at 1064 nm and 355nm for 10 ns pulses. The results suggest that the residual stress of HfO2 film is correlated with momentum transfer parameter, while both the ion energy and working gas flow maybe critical for the LIDT (absorption). The correlation between the microstructure and HfO2 film properties is discussed.

A three-dimensional (3D) system is developed with a microlens array (MLA) and a digital micromirror device (DMD) type spatial light modulator (SLM) to perform light field projection. In order to get 3D projections, a pixel value map, i.e. elemental images, is required to be loaded into SLM. Algorithm to render elemental images is developed in this study using ray tracing. The reconstructed 3D projection, which is the 3D output of the system, is examined by cameras at different focal positions. The result shows that the intended projection patterns are correctly reconstructed. The light field projection method can be extended to photolithography when photoresist is exposed to reveal the 3D structures of the intended projection. Compared with current 3D lithography, the proposed MLA based projection/lithography can reconstruct micro-structure with 3D curved structures in a single projection, which can significantly improve the 3D fabrication speed and quality. With the future implementation of optical compression and femtosecond laser, the proposed technique has the capability of conduct large area microfabrication with resolutions better than diffraction limit at a very high speed.

The application fields of Infrared spectroscopy are extremely wide from matter analysis of organisms to environmental observation. In wide-band spectroscopy, a pair of two different dispersive gratings is used. One is a high-order high dispersive grating according to the bandwidth of the detector; other is a low dispersive grating that separates the overlapping order. In this work, a low dispersion grating was fabricated on the incident surface of a conventional immersion grating to manufacture the world's first multifunctional Germanium immersion grating having two gratings in one device. Positioning accuracy with respect to three-dimensional space with our homemade cutting machine has an extremely good accuracy of less than 3nm RMS locally and less than 15nm RMS globally. The grating surface roughness is less than 3nm RMS. We introduce next-generation diffractive grating processing technology with extremely high freedom.

X-ray nanoprobes with 10 nm or sub-10 nm spatial resolution are highly desirable for the next-generation synchrotron beamlines due to the nanoscale imaging capability with high sensitivity to elemental, chemical and structural variations they provide. Multilayer Laue lens (MLL), a type of volume diffractive optics, was shown in theory to be able to focus X-rays to well below 1 nm [1]. In addition to this very high spatial resolution, it can also achieve much higher efficiency than conventional Fresnel zone plate [1]. An MLL is fabricated by sectioning thousands of planar depth-graded layers with nanometer thickness cross-sectionally into several to tens micron thick slivers. The section thickness is critical to achieve the optimum efficiency at desired energy. The requirement of high-aspect-ratio structure of an MLL presents enormous challenges in the post-growth processing, especially as the aperture size (deposition thickness) keeps increasing and therefore the residual stress increases as well. Sectioning without damaging multilayers becomes more and more difficult. At National Synchrotron Light Source II (NSLS-II), we have demonstrated that high quality MLLs can be successfully fabricated by combining mechanical polishing and focused ion beam (FIB) milling. The former removes most of the unwanted material and the latter is used for the fine and final polishing process [2]. MLLs with aperture size of 53 microns made by this method demonstrate around 10 nm focusing capability [3], suggesting that no additional aberration is introduced in the post-growth processing. Wedged MLLs are the best option to achieve sub-10 nm X-ray focusing, because they can produce higher efficiency compared with flat MLLs with the same section thickness [4]. However, sectioning requirement for a wedged MLL is more stringent because best focusing of a wedged MLL (in terms of both focus size and efficiency) can only achieved at a specific section thickness for one optimized energy. In this presentation, I will introduce the process, advantages, and technical difficulties of using the combined mechanical polishing and FIB method to make MLLs. The strategies to tackle the problems and make site-specific wedged MLLs will also be presented. [1] J. Maser, G.B. Stephenson, S. Vogt, W. Yun, A. T. Macrander, H. C. Kang, C. Liu, and R. Conley, “Multilayer Laue lenses as high-resolution x-ray optics”, in Design and Microfabrication of Novel X-Ray Optics II, edited by A. Snigirev, D. Mancini, Proc. SPIE 5539, 185-194, SPIE, Bellingham, WA, (2004) [2] H. Yan, R. Conley, N. Bouet, and Y. S. Chu, “Hard x-ray nanofocusing by multilayer Laue lenses”, Journal of Physics D: Applied Physics 47, 263001 (2014) [3] H. Yan, N. Bouet, J. Zhou, X. J. Huang, E. Nazaretski, W. H. Xu, A. P. Cocco, W. K. S. Chiu, K. S. Brinkman and Y. S. Chu, “Multimodal hard x-ray imaging with resolution approaching 10nm for studies in material science”, Nano Futures, 2, 011001 (2018) [4] H. Yan, J. Maser, A. Macrander, Q. Shen, S. Vogt, G. Stephenson, and H. Kang, “Takagi-Taupin description of x-ray dynamical diffraction from diffractive optics with large numerical aperture”, Phys. Rev. B, 76, 115438 (2007).

Infrared (IR) optic holds a key element over a broad range of advanced optical systems such as thermal imaging, night visions or laser-based sensing. Most infrared optical materials like chalcogenide glasses, however, suffer great transmission losses due to their high refractive index. Therefore, antireflective (AR) surfaces are necessary to enhance the optical performance of the IR optics by suppressing undesirable reflection at the optical surfaces and thus increasing the transmission. The AR-coatings commonly used for IR lenses in the contemporary optic market are expensive and environmentally critical. Instead, Precision Glass Molding (PGM), a replicative manufacturing method for the production of highly precise glass optics, becomes a promising solution to fabricate the AR-nanostructures on the chalcogenide glasses in a cost-efficient manner. The PGM process development starts out a multiscale modeling of the molding process, by which the form accuracy of the molded glass lenses is predicted at macroscale while the replication of the AR-structure is visualized at nanoscale simulation. This simulation necessitates a newly developed thermal-mechanical constitutive model to represent thermo-viscoelastic behaviors of the chalcogenide glass. Experimental validations of the form accuracy and the replicated AR-structure of the molded lenses demonstrate essential benefits of the simulation model. This paper focuses on the process simulation as well as the subsequent steps of mold manufacturing and glass molding itself. The success of molding AR-structures by precision glass molding promisingly satisfies the increasing demands for the high volume production of inexpensive IR optical elements in today’s optics and photonics markets.

The steadily growing thin glass market is driven by a vast amount of applications among which automobile interiors and consumer electronics are, such as 3D glass covers for displays, center consoles, speakers, etc. or as part of optics within head up-displays. Today, glass manufacturers are suffering from challenges brought about by the increases of shape complexity, accuracy and product variants while simultaneously reducing costs. The direct manufacturing method via grinding and polishing is no longer suitable because of its limited machinability for thin glasses in respect to fracture and its cost insufficiency due to the length of the process chain. Instead, replication-based technologies or thin glass forming become promising manufacturing methods to overcome the aforementioned technical and economic challenges. For instance, thermal slumping is only able to satisfy the most basic requirements and is in particular limited regarding the deformation degree and shape complexity of thin glass products. Technologies such as vacuum-assisted slumping or deep drawing are currently in development at the Fraunhofer Institute for Production Technology IPT and promise additional cost benefits. This paper introduces all potential process variants for thin glass forming. The suitability of different methods for process development, specifically process modeling based on either experimental-, simulation- or machine learning approaches (white box and black box models), will be addressed and discussed. Furthermore, process efficiency is examined on both an economic and technical level, where molding time, suitable geometries and accuracy are the focus. The methodologies presented in this paper aim at developing a guideline for glass manufacturers on determining the optimal strategy for the process development of thin glass production.

We fabricated a transmission silicone grating using two-beam interference method and imprint lithography, and evaluated its optical characteristics during a compression process. The grating pattern with ~0.4 μm depth and 1 μm pitch was created on a silicone surface by imprinting process with a photoresist mold to realize a simple, low-cost fabrication process. The first order diffraction transmittance of this grating reached ~10% at 633 nm wavelength. We also measured the relationship between the grating period and compressive stress to the fabricated elements. The grating period changed from 1 μm to ~0.8 μm by ~17% compression of the fabricated element in one direction, perpendicular to the grooves.

Optical metrology is a critical and complicated technique for the fabrication of precision optics which surface figure is better than RMS 1/30λ. The intrinsic systematic error of the experimental setup including the alignment error of the metrology tool and manufacturing error of the reference optics shall be calibrated carefully. Nevertheless, the measured consequence also includes the surface deformation caused by mounting supporter and gravity effect, which may result in a misleading judgment for surface figure correction, especially for mid- to-large optics. Besides the systematic error of experimental setup and deformation by an external condition of the optics, the environmental condition such as temperature drift, air turbulence, and vibration also affect the measured result. This paper proposes a method which adopts the magnitude and phase of each non-rotationally symmetrical Zernike coefficients grabbed from the multiple measurements from rotating the optics to analyze the absolute low-spatial frequency figures.

Femtosecond laser processing has been extensively used in micromachining, especially for the precision processing of hard and brittle materials. However, the precision of the materials ablated by femtosecond laser is not easy to control. This paper reports an experimental and theoretical study on the ablation characteristics of fused silica using high repetition rate femtosecond laser. An experimental study of microchannels milling on the fused silica was carried out. The influence of pulse energy, repetition rate, scanning velocity, scanning times on the size and morphology of the microchannels was obtained. Simultaneously, the experimental data on the depth and width of microchannels under different parameter combinations were acquired through the orthogonal experiment. The prediction model of aspect ratio was obtained by BP neural network algorithm. Finally, the verification test was established and showed that the experimental results were consistent with the theoretical results. It would provide a theoretical basis for further study on the microchannels fabrication of femtosecond laser.

A thermal deformation monitoring system was developed in this study by applying the thermocouple sensors and capacitive displacement sensors, along with a Long Short Term Memory (LSTM) Network Model classifier, for the alignment turning system (ATS). An ATS can simultaneously provide the functions of measuring the centration error and dimensions of the lens cell in-line, and machining the lens barrel housing with reference to the lens optical axis. The ATS can manufacture precise lens cells, applied for optical metrology, high numerical aperture objective lenses, and lithography projection lenses. While rising temperature, the thermal error would occur on hydrostatic spindle which build in ATS. Therefore, the predetermined machining point would offset, thereby resulting in the machining error. In order to acquire the oil temperature of rotor and the relative thermal displacement between hydrostatic spindle and turret, the thermocouple sensors and capacitive displacement sensors were assembling on ATS. According to the measurement of oil temperature and relative displacement, the thermal deformation monitoring system of ATS hydrostatic spindle was established. Cause of the high resolution of capacitive displacement sensors, the more precise measurement values could be obtain so that the monitoring system would have higher accuracy. LSTM is a variant of Recurrent Neural Network (RNN) and could remember longer information changes than traditional RNN. The thermal deformation monitoring system with LSTM could be applied to compensate the thermal error to improve the workpiece quality in real-time, and also could save time and money of warming up centering machines in the future. Results shows that the mean square error (MSE) and RScore of forecasting thermal error is less than 0.0002 and higher than 0.997, which is highly accurate forecasting.

In this paper, we propose a fabrication process based on Magneto-Rheological Finishing (MRF) for a reflective Spiral Phase Plate (SPP) with a continuous surface. The front surface of a nickel-plated aluminum disk is machined by diamond turning as a plane mirror, and spiral structure with low topological charge is generated by sub-aperture polishing tools, i.e., MRF. Interferometers are used to analyze the smoothness of the spiral structure, steepness of the center step and surface roughness of the random areas for the fabricated SPP. The results indicate that the direct-polishing approach can be a promising technique to fabricate high-precision SPPs.

The degree of passivation of the grinding wheel is gradually increased during the machining process, the friction between the grinding wheel and the workpiece is increased which causing the vibration and noise of the machine are changed. Therefore, the vibration and noise values could be obtained by using the vibration sensor and microphone. We use the spectrum analyzer to analyze the trend of the variation of vibration and noise signals. As the wear of the grinding wheel increases, the sound acoustic pressure in the range of 4.3 kHz to 5.3 kHz decreases. As the friction between the grinding wheel and the workpiece increases, high-frequency noise greater than 6 kHz are excited and the acoustic pressure increases. According to the experimental results, it is known that the wear state of the grinding wheel and the noise spectrum in generating process has a significant correlation. The cutting force of the grinding wheel can be observed by the noise spectrum of the spectrum analyzer to identify whether there is an abnormality in the processing process to optimize the grinding parameter immediately for avoiding the damage of the lens.

We report an interferometric method for smooth freeform optics from the amount of sub-aperture surface profiles. The overall experimental system is composed of a 5-axis precision stage and a sub-aperture measuring interferometer, which is carefully calibrated to achieve 2 nmRMS precision. The sub-aperture interferometer adopts a broadband source in order to maximize the reliability of profile measurement, and a preliminary assumption of the overall surface is derived from the measured local 2nd derivatives which is robust to tip/tilt alignment errors during the sub-aperture acquisition. The optical surface of a 200 mm diameter 2D polynomial freeform mirror is measured based on this system and traditional contact surface profiler for the cross-validation. The experiment shows the effectiveness of the system that the mismatch against a commercial interferometer is less than 20 nmRMS.

Image slicers have become a standard equipment in the field of astronomical spectroscopy. They are now widely used in most integral field spectrographs (IFSes) in order to detect and characterize distant galaxies or extra- solar planets. However, they are notoriously difficult to manufacture due to their multiple small tilted surfaces, but equipment such as that of AOFI (Advanced Optical Fabrication Infrastructure) of Universite Laval eases the process. In this regard, the team at AOFI has been tasked with the fabrication of the image slicer for the GIRMOS instrument. This paper presents the characterization of diamond turned RSA-6061 and AA-6061 T6 aluminum, and the definition of the different machining parameters, such as step size and tool radius, that could improve the surface quality of an aluminum image slicer. It also discusses the fabrication of the first prototypes at AOFI, that will eventually prove useful in the fabrication of the image slicer for GIRMOS, effectively lowering its risks.

In this paper, we propose a compensation method for the nanometer level of thermal drift by adopting long-short term memory (LSTM) algorithm. The precision of a machining process is highly affected by environmental factors. Especially in case of a single-point diamond turning (SPDT), the temperature fluctuation directly causes the unexpected displacement at nanometer scale between a diamond tool and a workpiece, even in the well-controlled environment. LSTM is one of the artificial recurrent neural network algorithms, and we figure out that it is quite suitable to predict the temperature variation based on the history of thermal fluctuation trends. We monitor the temperatures at 8 spots nearby a SPDT machine, and the neural network based on LSTM algorithm is trained to construct the thermal drift model from the time series data. Results of thermal drift prediction showed that the proposed method gives an effective model upon the well-controlled laboratory environment, and by which the thermal drift can be compensated to improve the precision of SPDT process.