This PDF file contains the front matter associated with SPIE Proceedings Volume 12778, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Freeform optics are becoming more prevalent in the optics industry. Designers recognize their ability to reduce optical system footprints, enable more complex systems, and match mold lines of their application. These benefits come with new challenges and requirements. As freeforms become more readily used, their geometries are becoming increasingly complex, surface finish tolerances are tightening, and desired manufacturing times are shortening. Just as advancing from spherical to aspherical advancement required adapting existing best-practices and developing new techniques, meeting the freeform manufacturing requirements will require a new manufacturing process. To successfully develop a manufacturing process for freeform optics, several requirements need to be met: the process should be repeatable and efficient, opportunities for human error should be minimized, and the process should be simplified such that high skill level technicians are not a requirement for success Fixturing and datum designs are key to making the process more repeatable and easier to set up as it simplifies moving the part between machines and metrology. On-machine probing makes part setup easier, minimizes the impact of operator skill level, and decreases part damage risks. Processes are developed to optimize the result of each step in the operation and minimize the time required by each following operation, which typically have lower removal rates and longer run times. The choice of metrology platform and error map types can directly affect overall processing time and ease of error map alignment for deterministic figure corrections. This paper presents OptiPro’s advancements in these areas to successfully manufacture freeform optics.

Hard ceramic and optical materials can present substantial challenges in manufacturing due to their tough mechanical properties. The properties that make these materials ideal for a variety of applications also makes them incredibly difficult to machine. Some of the biggest challenges in machining parts are minimizing the amount of sub surface damage (SSD) imparted into the material, slow processing speeds, and increased tool wear. The amount of SSD directly impacts processing time of these parts as additional finer tooling is required for the process or additional polishing time is necessary. Using finer tooling will produce more tool wear and slow down the overall process. To overcome these challenges, OptiPro Systems has developed an ultrasonic assisted grinding technology, OpitSonic, which has been designed for the precision optics and ceramics industry. OptiSonic utilizes a custom tool holder designed to produce oscillations, in the micron amplitude range, in line with the rotating spindle. A software package, IntelliSonic, is integral to the function of the platform. IntelliSonic can automatically characterize tooling during setup to identify and select the ideal resonant peak to operate at. While grinding, IntelliSonic continuously adjusts the output frequency for optimal grinding efficiency while in contact with the part. Using a variety of instruments, tests have proven to show a reduction in SSD while using OptiSonic, leading to decreased processing times and minimized tool wear. This paper will present the challenges associated with these materials and the solutions created to overcome them.

Traditional optical manufacturing techniques such as abrasive polishing and diamond turning create precise surfaces by removing material from the optical surface of a mirror. Such techniques often require many cycles of removal and metrology and can leave surface roughness or tool marks that negatively affect the straylight properties of an optical system. These residual artifacts often necessitate expensive postprocessing such as ion beam finishing. Limiting straylight is particularly crucial in the design of reflecting coronagraphs or optical systems that are sensitive to scattered light, for example for exoplanet detection, where even low-level scattering can degrade contrast ratios below the sensitivity needed to detect exoplanets. We introduce a non-contact method for shaping thin front-surface mirrors to avoid tool artifacts. Using laser techniques to alter local surface stresses, we deterministically introduce ≥ 8 waves (632.8 nm) of shape to 2 mm thick substrates. A deterministic method for creating arbitrary surface figures is under development and calibration.

Rotative printing technologies are an approach to manufacturing polymer optical waveguides with high throughput for applications such as electro-optical circuit boards (EOCB) or smart packaging. Processes presumably originating in graphical applications apply defined amounts of polymer onto a polymer substrate. Unlike graphical printing, the use of these processes to manufacture functional waveguides underlies different requirements regarding material transfer, structure of the printed polymer, and multi-layer stacking of functional layers. This work applies the manufacturing processes gravure printing and flexographic printing to realize waveguide cores onto PMMA substrates. Therefore, a modular printing machine with high positional accuracy between multiple printed layers is used. The waveguides are further cladded with another PMMA substrate using thermal lamination. The processes are evaluated according to waveguide geometry and optical parameters. Material transfer per layer, resulting geometrical quality, and aspect ratio of the waveguides are compared regarding their manufacturing process. Functional tests are conducted as optical attenuation measurements to evaluate the waveguide's macro range performance. Using these results, the potentials of each process for an upcoming production of fully-printed cladded waveguides are determined and showcased.

New solutions are required for short-range optical transmission without lithography due to the complex and inflexible manufacturing processes. Glass is an excellent material for optical applications. Still, few microprocessing technologies are available, which are limited in precision and design freedom. A new glass micromachining process called Laser Induced Deep Etching (LIDE) can accurately machine many types of glass without generating micro-cracks, introducing stress, or causing other damage. This study uses LIDE to produce carrier substrates out of glass for integrated optical systems. Due to its transmission characteristics and refractive index, it also functions as optical cladding for integrated polymer optical waveguides. U-shaped cavities are etched into the glass and filled using the doctor-blade technologie with conventional liquid optical polymers, which are then globally cured. This novel manufacturing method is called LDB (LIDE-Doctor-blade). Optical waveguiding in the visible to near-infrared wavelength range is possible by the higher refractive index of the cured polymer. The waveguide is embedded in a near-surface cavity, with no additional upper cladding other than air to the environment, created by a combination of subtractive and additive manufacturing processes. The exposed area can affect transmission quality, and this study purposely exploits this by applying fluids with different properties, such as refractive index and viscosity. Changes in intensity are analyzed and evaluated to demonstrate a sensory function.

Thermal changes during diamond turning always present to some degree. For small parts with relatively short cut times, the effects can be minimal with modest thermal management. As parts become large and turning times increase, thermal effects can manifest themselves in a variety of ways. In this paper, we describe three different unique applications where temperature cycling and drift modified the original plan for part fabrication: a roll-to-roll embossed microprism array, a large diameter acrylic lens, and diamond turning a large mandrel.

Tungsten carbide (WC) offers high-strength, high-melting points, and exceptional toughness, with critical applications in industries such as optical molding. Precision machining of WC typically uses grinding operations where tool wear is a significant issue, especially for small geometries required for the consumer electronics industry. Single-point diamond turning (SPDT) is another option for precision machining small features but excessive tool wear prevents this from being a viable option. Innovative approaches, such as in-situ laser-assisted diamond turning, have demonstrated remarkable potential in alleviating tool wear issues and generating optical-quality surface finishes. Laser-assisted techniques, leveraging laser energy for ductile mode machining, mitigate material cracks or fractures. This study delves into the intricate relationship between diamond tool geometry, particularly the rake angle, and ductile regime machining dynamics. Precise selection of diamond tool geometry and rake angle is crucial for desired surface quality. The experimental setup involves specialized equipment like a UMT Bruker tribometer with a modified OPTIMUS system to investigate the impact of tool geometry, specifically the rake angle, in micro laser-assisted material removal on tungsten carbide. The goal is precise and controlled material micro laser-assisted ductile mode removal while minimizing damage or subsurface defects. Results highlight that the rake angle significantly influences the critical depth of cut, with a -25° rake angle proving advantageous, especially when combined with higher laser power. Laser power and tool geometry are pivotal parameters for optimizing hard and brittle material machining, offering valuable insights for precision engineering applications.

Cylindrical lenses are becoming increasingly important in the optical industry. They are used, for example, in illumination systems in microlithography, in lenses for recording and projection of cinema productions or also in LIDAR systems, such as those increasingly used in the automotive sector. There are many variants of cylindrical lenses and thus also different parameters that need to be measured. In addition to the characterization of the centering errors of single lenses, it is also required to characterize the centering errors of already fully assembled anamorphic lenses. For a spherical surface it is sufficient to describe the centering error with a single parameter, the surface tilt error of the sphere. Geometrically, a cylindrical surface is described by a line. This is typically the cylinder axis or the apex line. The latter results from the projection of the cylinder axis onto the cylinder surface. For the complete description of the centering error of this line, in principle 3 quantities are needed: - The decentering (offset) of the cylinder axis to a given reference line. - The angle between the cylinder axis and the reference line. (“Clocking”) - The angle between the cylinder axis and a base plane (“Wedge error”) The reference line can be either a mechanical edge or another cylinder axis. The measurement procedures for all centering errors including measurement results of typical samples will be presented. Finally, we will present the so called MultiLens© measurements of an assembly of cylindrical lenses.

In 2017, the European Southern Observatory (ESO) awarded a contract for the Polishing, integration and final figuring of the Segment Assemblies of the primary mirror (M1) for the Extremely Large Telescope (ELT) to Safran Reosc. Since then, the design and commissioning of a production unit dedicated for ELT M1 has been accomplished and the plant have been producing many mirrors since spring 2022. We present the status of the project, some lessons learned and highlight the successes that have been achieved so far.

The next generation of ultra-precision optics requires rapid and cost effective surface figuring technology. Different manufacturing technologies exist: magnetorheological finishing, chemical mechanical polishing, and ion beam figuring; however, these technologies are slow and lead to expensive optics. Plasma figuring, operating at atmospheric pressure, is a cost effective method for figure correction of ultra-precision optical surfaces. In this presentation, fast figure correction of optical surfaces is reported using the Satisloh Plasma Polisher (SPP). The technology uses a reactive plasma jet to surface figure flats of fused silica. The plasma jet is powered by a solid state microwave generator, which operates in pulse mode to reduce the plasma temperature hence increasing the repeatability of the etched trenches. The trenches are characterised using an interferometer. Each trench follows a Gaussian function. Material removal rates can range from nm³ to a mm³ per minute, which can result in surface form error reductions of 90% in a single iteration. The surface roughness is measured using a white light interferometer and shows no degradation in the surface finish.

Aspheric optical lens surface is getting incorporated more into optical systems for improving different aspects of the system such as resolution, aberration corrections, weight, size etc. However, in comparison to a spherical lens, an aspheric lens poses new challenges in the alignment of the optic as the aspheric geometry consist of a single axis of rotational symmetry in comparison with a sphere which is radially symmetric at any point on the surface. This paper is intended to describe different methods which can be used to specify the centration of an aspheric lens component and how these methods should be chosen according to the intended assembly process.

Magnetorheological Finishing (MRF®) is a polishing process with a wide parameter space. Through the selection of various fluid compositions, wheel sizes, and other process settings, a large suite of possible tools is available. Most of the process space has been engineered to satisfy final figuring in which typically hundreds or possibly thousands of nanometers of removal are required. For larger aperture optics and/or higher amplitude corrections, there is interest in efficiently removing larger volumes of material. Continued optimization of the fluid delivery system, specifically the nozzle design, has resulted in dramatically improved removal rates. Initial process optimization has been performed to integrate these improvements into production. A new nozzle design produced improved removal rates of up to 200% relative to the standard nozzle designs. With the new design, several factors needed to be investigated to verify its suitability for production. Foremost among these was the performance around the edges of the polished aperture. Transitioning an MRF tool onto an optical surface typically produces a zone where the tool shape and/or rate differs from the characterized tool. The size of the zone scales with the size of the tool, and within this zone the removal is not well predicted. Varying the removal function (also referred to as the spot) size around the edges to mitigate this effect was assessed with promising results. Finally, the stability of the tool was characterized. The stability of the tool affects global unpredicted removal errors, particularly in higher spatial frequency bands. Preliminary results have shown performance at least comparable to the standard designs.

As the demand for lower surface roughness precision optics increases for high tech applications, polishing solutions that can achieve low surface roughness are needed. Pureon is committed to developing advanced polishing solutions for the precision optics market. Cerium oxide is one of the most common materials used to polish precision optics, and the surface quality that can be achieved depends on the mean particle size of the material, the purity of the material, polishing pad, and slurry chemistry. To achieve low surface roughness, Pureon has developed an advanced final polish cerium oxide slurry with a mean particle size of ~ 0.1 μm (nanoceria formulation) and narrow particle size distribution. To determine if this nanoceria formulation can achieve low surface roughness, the formulation was compared to Ultra-Sol® Optiq which is an industry leading slurry for precision optics and has a mean particle size of ~ 0.45 μm. The initial experiments were performed on OPTIVISION™ 4540 pads for both Ultra-Sol Optiq and nanoceria formulation with fused silica glass. The surface roughness was improved by 30% when using the nanoceria formulation compared to Ultra-Sol Optiq. The surface roughness was measured with a 3D optical profiler. An in-depth study of how the nanoceria formulation can improve surface quality for diverse types of glass will be presented, using fused silica as an example material.

Laser-assisted diamond turning has been shown to reduce tool wear, improve productivity, and achieve better surface specifications (including roughness and form) for traditionally diamond turnable materials for infrared optics. Amorphous glass being typically harder than IR materials, thus, diamond turning is less effective compared to traditional grinding and polishing methods. However, traditional grinding and polishing come with drawbacks, such as introducing significant subsurface damage ranging from 20-60 μm, necessitating removal during the polishing process, known as grey out. During grey out polishing, the optical axis can wander, leading to errors between the mechanical axis and optical axis when polishing aspheres. Moreover, sub-aperture polishing steps add mid-spatial frequency errors with each subsequent iteration before form convergence to a low irregularity. Laser-assisted diamond turning for amorphous glass shows promise as a method for rapidly producing near-net optics with minimal sub-surface damage.. This enables two critical gains for optics manufacturing: 1) glass optics can be polished to finished specifications much more quickly than with traditional grinding and polishing; and 2) mechanical tolerances such as wedge and sag can be maintained with precision, reducing manufacturing errors in aspheric optics. In this work, we present data showing that subsurface damage can be reduced to <3 μm for glass optics. Additionally, we demonstrate that form accuracy remains better than 500 nm for even after 10 or more diamond turning passes, indicating extended tool life and high level of conformity to near-net shape.

Ion beam machining has a long tradition in the production of classical high-end optical components. Sophisticated telescopic or lithographic optics have long been made possible by deterministic and highly reproducible focused ion beam machining on various materials of optical technologies. The entire process of producing such delicate components as spheres, aspheres, plano optics or freeforms still depends heavily on the optician's experience and ultimate patience in mastering the alternation between interferometric inspection and the highly-precise, locally determined material removal. With focussed ion beam machining lowest figure errors in PV of less than lambda/200 and micro-roughness values of less than rms = 0.1 nm can be achieved through precisely planned iterative machining. In contrast to long-lasting production, today's industrial and research applications in the fields of precision optics and semiconductors demand the same or higher qualities, but also higher quantities and productivities. New process approaches have to be found and descriptions for higher material removal without compromising quality have to be created. The authors discuss how productivity can be implemented in ion beam machining.

This paper investigates the feasibility of measuring surface form of cylindrical optics using non-contact multiwavelength interferometry. Two plano-convex lenses, one with an acylindrical prescription and the other with a cylindrical prescription were measured on a non-contact multiwavelength interferometer and their surface form error was evaluated. To corroborate the results obtained from this, the two lenses were measured on a contact type PGI (phase grating interferometer) gauge, and the peak-to-valley (PV), root mean square (RMS), and radius of curvature (RoC) parameters were quantified to compare the 3D height maps obtained from these two different measurement methods. It is shown that there is a good agreement between the multiwavelength interferometer and PGI gauge and the key differences including measurement setup and cycle time between the two methods are discussed.

For aspherical and freeform surfaces not only the surface form error but also the position of the surface relative to external references is important (e.g. fiducials like markers, the outside edge, plane orthogonal surfaces, dowel pin holes). The NMF non-contact measurement machine range for freeform optics by Dutch United Instruments (DUI) can be employed for measurements during the entire production process, measuring ground, polished and coated optical surfaces. This machine has now been extended with a second sensor, either a marker camera or a tactile probe, to measure the position of the optical surface relative to the references features.

Off axis parabolas (OAPs) allow for more confined and intricate optical system designs, but meeting tight irregularity and slope specifications can be difficult due to distortion in null test setups. This distortion is exacerbated with steeper off axis angles (OAA). This paper will show different methods to correct distortion in an autocollimation measurement of an OAP, and how to determine when to use each method.

We have designed and simulated the interferometric null test of a rectangular aperture freeform mirror using a spatial light modulator or SLM as the reconfigurable computer-generated hologram. We use a high dynamic range Shack- Hartmann wavefront sensor (SHWS) to monitor the SLM output. Here, we focus on benchmarking the measurement of the SLM output using the SHWS for rectangular apertures with a 50-wave peak-to-valley astigmatic wavefront designed in the Chebyshev polynomial basis. The error between the SLM output and the nominal wavefront input is compensated through an iterative optimization strategy to sub-diffraction limited RMS wavefront error.

Protective glasses are used to protect camera modules and optical sensors from mechanical stress or environmental influences. To ensure consistent quality and avoid image distortion caused by these optics, the transmitted wavefront needs to be controlled and defects like inclusions need to be detected. This way, identification of defective parts and monitoring of the manufacturing process becomes possible. In this paper we discuss transmitted light test setups for wavefront testing of optical windows and the accuracy and stability that can be achieved. Additionally, we show procedures for wavefront-guided alignment of optical systems. The second part of the paper deals with the testing of fast steering mirrors, which are often used in free-space communication or fast scanning applications. The reflected wavefront carries information about the quality of the 3D surface shape. We demonstrate how to assess the mirror quality using a reflected light test setup.

We report on an optical, non-contact, thickness measurement system for materials that are opaque in the Near infrared (NIR) through ultraviolet (UV) wavelength range. While measurement options do exist, they must either physically touch the sample or rely on an assumed bulk distribution of material. In addition, optical and semiconductor materials are often highly sensitive to contamination and greatly benefit from noncontact metrology. The authors have adapted techniques used for the Lumetrics Optigauge 2000 low coherence interferometry (LCI) system to build a 2.8 μm LCI system using non-silica optical fibers to direct the probe signal. A (100) Silicon (Si) test sample was selected as a control because it can be measured by both an Optigauge II and the MIR-LCI system. In this work, the authors successfully measured materials that are transparent in the midinfrared (MIR) range, such as Germanium. The authors speculate that MIR-LCI will enable wedge, thickness, flatness, and other measurements performed using an Optigauge II system for MIR transparent materials.

The precision measurement of the radius of curvature of optical surfaces is mainly done using interferometric methods. Most general is the two-position method with a measurement at the cat’s eye and confocal positions, where the radius of curvature is given by the axial displacement of the test piece between the two positions as obtained e.g. from a distance measuring interferometer. This becomes more difficult for surfaces with long radii and large R-numbers, especially so for convex surfaces. Typical examples are laser cavity mirrors, or lenses with very long focal length. For this group of very shallow test surfaces the possibility exists to measure the radius of curvature with a flatness interferometer. It requires just a single measurement without axial part displacement, and represent a very quick and simple way of measuring long radii. However, this method does not operate at or near a fringe-null since a curved surface is compared to a flat reference wavefront, as opposed to the two-position method where the curvatures of the reference and test wavefronts are matched. Hence a more detailed consideration of measurement errors is required to establish the accuracy of the measured radii. This analysis shows that a carefully calibrated low-coherence flatness interferometer can provide radius measurements accurate to better than 1 part in 2000, or 0.05%, with the additional advantages of suppressing unwanted backside fringes. This presentation details the error analysis, and presents measurement results from the OptoFlat low-coherence flatness interferometer.

Phase-shifting interferometry is the premier measurement technique for high-precision surface form metrology. Generally, the measurement cavity is illuminated with a stationary, on-axis, point-like source of coherent light situated at the interferometer source plane. We describe how to enable a variety of useful functions to aid interferometric metrology applications by dynamically moving the source point during a phase-shifting measurement using steering mirror technology. Called Dynamic Illumination, these motions describe trajectories that often take the form of geometric primitives like points, lines, arcs, circles, and spirals. A fixed point on the optical axis represents conventional operation, but measurements using different trajectories enable different functions. We highlight three exemplary functions in this paper; phase shifting, autofocus, and coherent noise reduction techniques.

There are two basic methods of calibrating a transmission sphere without use of an external artifact, statistical or shear. In the low NA range where shearing is the preferred method, the calibration is difficult to perform precisely because it is hard to measure the shear distance or rotation of the reference surface precisely. If the reference is a Fresnel zone CGH, then there are two centers of curvature that provide an axis that can be located precisely. We show theoretically and experimentally an absolute method of calibrating a TS using one rotational and one translational shear.

Deflectometry (shape measurement of a mirror from the distortion of the image of a monitor screen displaying fringes) has been known for a long time, but suffers from intrinsic features that make accurate absolute measurements very difficult. In particular, all the metrological quality depends on the ultra precise identification of the system geometry: ray trajectories in the object space, shape of the monitor screen, position of this screen and position of one point of the measured object, all these in the camera frame of reference. We present an instrument that permits all these identifications in a simple push-button way. The fundamental ambiguity of deflectometry (a single measurement may correspond to an infinite number of object shapes, due to the unknown constant after slopes integration) is raised with our patented coaxial deflectometry approach: two measurements are made with an axial movement of the camera, and only one shape is compatible with these two measurements. We present the identification methodology of the system, and results for absolute measurements of spheres, aspheres and freeforms, within a λ/40 accuracy, with some comparisons with results obtained with a Taylor-Hobson LUPHOScan®.

With labor shortages and difficulty in getting experienced technicians, automation provides an opportunity to increase production and efficiency with a dwindling labor pool. Repetitive tasks such as machine tending and cleaning parts are easily automated with a robot to free up technicians to perform other more demanding tasks. These repetitive tasks can be boring, fatiguing, and menial, leading to worker burnout. Automating these tasks can improve working conditions and morale. Automation increases production rate and productivity. By communicating directly with the machines, a robot can reduce reaction time between processes, reducing down time. Automation provides consistency and the opportunity to run lights out, 3 shifts or over weekends, without breaks, increasing machine up time and throughput. It also reduces labor cost by reducing the number of employees required to hit production numbers. This labor savings results in a quicker return on investment. To help customers automate, OptiPro offers a robotic beveling solution, as well as other off the shelf and customized solutions to meet any required demands. The Revel is an automation cell that takes optical blanks and bevels both sides. OptiPro has created an easy-to-use interface so any operator can run it without knowing how to program a robot. It is set up to give flexibility in running many part geometries, tooling types, and different “recipes” based on the parts provided. OptiPro has also developed part loading for machines including cells which combine multiple machines such as a generator, polisher, cleaning stations, and even metrology to produce completed part surfaces.

Machine learning has become a core part of smart factories and Industry 4.0. In our work, we extend the use of machine learning for quality prediction of a thin glass product formed using a Non-isothermal Glass Moulding (NGM) process. As the form shape of a glass lens requires multiple variables to describe, Multi-Target Regression (MTR) is suitable for the same. Many MTR models are able to provide intuitive insights into the prediction target(s). We present a data pipeline that employs bootstrapping-inspired sampling for robust feature selection, modelling and validation for small dataset. The results demonstrate how MTR models can be used for prediction with dataset with high dimensional time series input and multiple targets.

The alignment turning of mounted optics and active elements grows in demand for industrial applications. Latest developments cover the measuring of aspheres and free forms, TO canned active laser elements and entire sub assemblies. Due to a growing demand in lithography applications, stainless steel mounts are more commonly used. The machine introduced is performing alignment turning based on a chuckless, fully digital approach. Speeds of up to 3000 rpm are possible to achieve higher cutting speeds, lower cutting forces, and greater productivity. Integration of inline metrology provides an automated solution for finding tilt and shift in various lens designs and materials, including aspheres and infrared materials. The result is faster and more reliable alignment of mounted optics and active elements, opening the possibility to higher production capacity and more affordable processing.

Tightening specifications and increasing demands for high performance optical coatings continue to drive advancements in many areas of the optical manufacturing industry. To ensure customer confidence, test and verification methods must be created to measure tighter tolerances than ever before for all aspects of thin-film quality control, including reflectance, transmittance, absorption, scatter, laser-damage threshold, lifetime stability, environmental durability, filter-edge steepness, deposition uniformity, and induced stress, to name a few. This talk will outline emerging performance requirements for optical thin films and the metrology solutions being developed to satisfy them.

The need for high and low refractive index materials for antireflective applications and waveguides continues to grow. Growing demand in data processing for data centers and new computational technologies take advantage of light as the new medium. High and low refractive index materials are needed in silicon photonics, augmented reality, and virtual reality (VR) applications, CMOS image sensors and micro-OLED applications. Designing these materials for spin and dip coatable depositions facilitates process flexibility to optical device manufacturing FABs and similar manufacturing facilities. Materials that are processable as spin-coated films with low refractive index of less than 1.25 are presented. These materials are based on a combination of pore size and material size control approaches. Materials presented in this work are adapted from University of Oslo (UiO-66)–based Metal Organic Frameworks (MOFs). A key advantage to this approach is that these films are processable at low temperatures, unlike several porogen-based approaches. This allows for these materials to be processed on plastics.

Among the high challenges of coating technology for optical interference filters and dielectric mirrors are deposition precision and stable reproducibility. These requirements are already very demanding for micro-optical substrate surfaces or optical components below 200 mm aperture area, especially when volume production with high quantities is also involved. Magnetron sputtering technology offers a suitable process that also allows the high precision and stable reproducibility required for alternating layer systems to be transferred to large-area optical substrates. Markets such as AR/VR/XR or automotive are driving demand for interference optical filter and reflective coatings on large-area components. They find application for example for VR glasses, in projecting systems (HUD) or functional interior displays. In the talk, coating solutions required for this purpose for aperture areas up to 300 mm and beyond will be presented and technical challenges for optical manufacturing will be discussed. Some coating results will be presented and the coating of large optics for laser technology will also be briefly covered.

Prism coupling refractometry is an often-overlooked refractive index measurement technique. It is significantly different from other common refractometry techniques, as it does not require the complex geometry and costly sample fabrication associated with the minimum deviation method or interferometry, nor any assumptions about the material properties as in spectroscopic ellipsometry. Lastly, with proper calibration, it can be used to measure the index to the third or even fourth decimal place, out-performing most Kramers-Krönig-based methods. Here, we report on the design, construction, operating procedure, and data analysis for an infrared prism coupling refractometer and its implications on both work in the lab and as a common device for optical shop testing.

Achieving precise tolerances in the assembly of optical components is crucial for the performance of off-axis optical systems. This study focuses on the design and evaluation of assembly methods and mechanisms of an Offner spectrometer with the goal of demonstrating their capability to achieve tolerances within 40 microns. The methodology involves the development of assembly methods and mechanisms specifically tailored for off-axis optical systems. Representative models of optical components and custom adaptors were designed and manufactured to facilitate the assembly process. Procedures were devised for setting up, repositioning, and locking the representative models. The proposed methods and mechanisms were evaluated using measurements from a Coordinate Measuring Machine (CMM). The accumulated tolerance in each step of the assembly process was analyzed, ensuring that the overall performance met the desired specifications. The findings validate the effectiveness and reliability of the developed approach, offering valuable insights for the design and implementation of similar systems.

Communicating fabrication tolerances is a vital part of the optical manufacturing process. The most common surface form tolerance is peak-to-valley (PV) irregularity, and its specification and evaluation has largely remained unchanged for decades. Fabrication, testing, and computation capabilities, however, have evolved considerably over that time, exposing PV’s extreme sensitivity to outlier data points. When everyone was using the same measurement and analysis technique (visual inspection of test plate interferograms), this sensitivity was of secondary concern to ease of computation. Today, however, numerous measurement techniques are viable for evaluating surface form, computation power is cheap, and different measurements of the same surface can easily result in wildly different PV results. This creates confusion as to whether a surface conforms to tolerance or not. To address this issue, we propose standardized methods for evaluating a PV tolerance value that are resistant to outliers. We first provide an example of the problem on an actual surface measurement and demonstrate how trimmed PV estimators can mitigate it. We review two such estimators, robust peak valley (PVr) and clipped peak-to-valley (PV%). We then review the conceptual trade-offs involved with choosing an appropriate estimator and demonstrate estimator behavior on a variety of simulated surface profiles. Finally, we explore the challenges in adopting a more reliable PV metric and outline the plans for updating the ISO 10110-5 surface form standard to achieve this.

A study was performed to investigate edge performance as a function of the mechanical edge profile. There are many edge profiles to consider. A baseline set of curved, straight and corner edge profiles was chosen for MRF finishing and analysis. Each sample edge profile was subjected to a series of uniform removal MRF finishing runs, only considered the leading edge. The results of this study provide a starting point for further investigation and mitigation of edge effects for different profiles during MRF finishing.

An in-depth study of the total process solution from grind to final polish was performed for borosilicate-crown glass and fused silica. SQUADRO-G2 grinding pad and the industrial standard fixed abrasive grinding pad were compared on a double-side tool. The surface roughness and the material removal rate were compared for the grinding step. SQUADROG2 had a comparable material removal rate for fused silica and a higher removal rate for borosilicate-crown glass. After the fine-grinding step, samples were polished with Ultra-Sol^® Optiq on various polishing pads. The processes were studied by comparing removal rates, surface quality, and the amount of material removed to achieve a low surface roughness, defect free substrate post-grinding. There was no difference observed for the finishing of glass that was ground with SQUADRO-G2 grinding pad and the standard fixed abrasive grinding pad. Furthermore, we offer some compelling case studies for achieving superior surface quality in the final polish operations.

We present a new experimental method for assessing subsurface damage (SSD) on optical glasses processed using fs-laser. The method employed nanoindentation and Raman spectroscopy to characterize material damage. Statistically, our method shows over 95% confidence for SSD depths of over 55 nm. According to our results, the fs-laser processed surfaces with optimized processing parameters revealed no detectable SSD, thus establishing the feasibility of fs-laser polishing for precision optical manufacturing.

We report an initiative on promoting sustainability in optical manufacturing by repurposing waste materials as bioplastic diffractive elements. Bioplastic diffraction gratings are fabricated from three chitosan solutions via soft lithography. Chitosan is prepared from seafood waste in the form of powdered crab shells through demineralization, deproteination, depigmentation, and deacetylation. For soft lithography of chitosan gratings, a mold is constructed from a polydimethylsiloxane (PDMS) grating replica of a commercial master grating with groove density of 600 lines/mm. The three chitosan solutions are each poured into the PDMS mold and allowed to harden. Once fully cured, the chitosan replicas are carefully extracted from the mold. We perform diffraction experiments at normal incidence with an Ar+ laser operating at 514.5 nm and 25 mW. Measured first-order power efficiency of the unmodified chitosan grating is 0.7%. The bioplastic gratings made from chitosan-starch and chitosan-glycerol both exhibit a first-order diffraction efficiency of 0.5%. These values are comparable with the 0.9% first-order efficiency of the PDMS replica used in the molding process.

In this study, our aim is to improve the efficiency of the optical manufacturing process employing magnetorheological finishing (MRF) by quantitatively analyzing the MRF response characteristics that vary according to the type and size of low-spatial frequency. Dimension-variable patterns were devised based on the dimension of the tool influence function (TIF), consisting of two types: a width-variable pattern and a height-variable pattern. These dimension-variable patterns were utilized as input data for the MRF corrective polishing system. The resulting residual figure error of the patterns generated through the MRF corrective polishing system was calculated and expressed as output data. Furthermore, to quantify the MRF response characteristics for low-spatial frequency, the relative error is presented by comparing the input data and output data. The results indicate that the MRF polishing performance for low-spatial frequency is influenced by both the type and size of the frequency, and these trends can assist in devising sophisticated and efficient MRF strategies for manufacturing ultra-precision optical surfaces.

Optics for accelerators require extremely low surface roughness (SR) to achieve high reflectivity due to the very short wavelengths of light used. Diamond turning (DT) is one of the leading machining processes for manufacturing optical components, and is widely used because of its high material removal rate and the ability to obtain optical surfaces with a SR of a few nm or less. There have been many studies on the prediction of SR in the DT process, and many SR prediction models have been proposed for the expression of it. However, when the SR is nm or less, the proposed SR prediction models show different results from the actual results. Aluminum has been used as a material for optical components used in the DT process due to its excellent machinability and high reflectivity, and it is a material that has been used as an actual processing material when proposing the SR prediction model. In order to use aluminum mirrors as optical components for accelerators, their SR must be generated to nm or less. In this study, we have compared and analyzed the nanometer SR of two aluminum materials to fabricate Al mirrors used in infrared optical systems for accelerators.

Polycrystalline zinc sulfide (ZnS) is a widely used optical material especially for infrared applications. After ultra-precision diamond turning (DT) machining of the material in ductile regime, surface roughness of a few nanometers is achievable. However, the traces of crystal structure were not only visible on the DT machined surface but it also showed the steep ups and downs on the surface profile, although the same depth-of-cut was applied to the whole surface. In this study, it was hypothesized that the ups and downs on the surface profile might be affected by the crystallographic orientation and elastic recovery of each grain on the surface of ultra-precision DT machined ZnS. The relationship between the crystallographic orientation and elastic recovery of the material was investigated using electron microscopy with electron back-scattered diffraction (EBSD) and nanoscale scratch tester. The results showed certain grain orientations exhibit higher levels of elastic recovery, leading to increased surface roughness. These results highlight the importance of considering crystallographic effects in the machining process of ZnS to achieve desired surface quality.

Zinc sulfide (ZnS) exhibits unique properties that make it highly suitable for applications as a multi-wavelength optical element. Its transmittance shows significant improvements in the visible light and near-infrared regions when subjected to high-temperature and high-pressure processes. However, the mechanical cutting of ZnS is limited due to its brittleness and polycrystalline properties. In this study, we propose the feasibility of employing ultrasonic vibration cutting to enable the mechanical cutting of polycrystalline zinc sulfide. The objectives are to analyze both the ductile mode machining and brittle fracture behavior while addressing the issue of spring back encountered during the diamond turning process. Analysis is conducted on cutting parameters, including vibration amplitude, spindle speed, cutting depth, and feed rate, to evaluate their impact on the cutting process. The results showed that we establish ultrasonic vibration cutting can indeed lead to improved cutting quality under specific conditions. We demonstrated the potential of ultrasonic vibration cutting as a promising alternative technique for the precision machining of polycrystalline zinc sulfide. The resolution of the spring back problem represents a significant advancement, potentially enabling the manufacturing of high-quality optical elements using polycrystalline material.