This PDF file contains the front matter associated with SPIE Proceedings Volume 12298, including the Title Page, Copyright information, and Table of Contents.

Micro lens arrays made of glass are optical components which, due to their complexity, can fulfill the function of many larger lenses at the same time. Optical arrangements can thus be miniaturized and made lighter. The production of such elements can be a challenge, especially for medium and small quantities. Therefore, at the ifw Jena, two direct production methods of such elements are being investigated: laser ablation with ultrashort pulsed (USP) lasers and ablation with a short-pulsed CO₂-laser respectively polished with a cw-CO₂ laser. The experiments show a good homogeneity of the lenses as well as a high process speed.

Chemo-mechanical polishing processes that are used to remove grinding marks are a major cost driver in asphere production. Especially when machining glasses that are prone to fracture from grinding subsurface damage can be substantial. As a result, subsequent polishing times can be extremely high. In order to reduce polishing times and increase process stability SwissOptic established an ultra-precision grinding process. Here, we compare process times and surface figure errors for two processes. The first process represents a standard process in asphere production with grinding, polishing and fine correction. The second process adds an ultraprecision grinding step before polishing. As a result, we find that cumulative process times and resulting figure errors are much lower if we apply ultra-precision grinding.

Plasma Jet assisted smoothing of rough ground optical surfaces is presented. An accurate temperature regime during the process is inevitable to achieve a uniformly smoothed surface. The possibilities for in-process temperature control are demonstrated on the example of Fused Silica and N-BK7® polishing. For both materials, the surface roughness RMS value can be significantly reduced by a factor of 20 to 1000 depending on the material and the initial ground state. An annealing step after smoothing is necessary to minimize birefringence caused by internal stress. The achievement of the existing requirements for precision optics is demonstrated.

Modern high-performance optical systems require new technologies for alignment and joining processes. With the established OptiCentric® Bonding 5D TRIOPTICS offers a technology that provides high-precision lens mounting based on adhesive bonding. With innovative alignment bonding in 5 dimensions, the lens surfaces are aligned to the tube with accuracies below 1 μm in x, y, z direction and below 2 arcsec in Θx and Θy direction. This fine-adjustment method doesn’t dependent on mechanical tolerances because the lens can move freely in the frame. By using high-resolution autocollimators as well as tactile and optical distance sensors the accuracy of each lens is checked after each step of machining. This procedure facilitates the stacking of several lenses into one tube without further costly alignment steps of sub-cells. This reduces the process steps and makes the multilens mounting into a tube more efficient. Furthermore, glue bonded lenses without sub-cells save space and weight due to waiver of set-screws and shims. Integrated into the production line this technology allows a greater degree of accuracy of optical systems and new design opportunities for more compact and higher-quality lenses. The highly flexible OptiCentric® Bonding 5D can be quickly converted to other types of lenses. This technology is also suitable for clean room applications.

In industry, the use of high-performance, high-precision and, at the same time, lightweight optomechanical imaging systems is becoming increasingly important. The use of aspherical surfaces is playing an increasing role as the number of lenses can be reduced and dimensions and weight can be minimized significantly. In the case of an asphere, on the other hand, decentering is possible as both a displacement and a tilting and this is completely independent of one another. Therefore, the aspherical semi-finished products must be subjected to certain centering rules during the grinding and polishing process and used on the production spindles in an optimized and adjusted manner in order to avoid rejects during production. A subsequent centering process, as is usual with spheres, is then no longer possible. The internal centering error in an asphere-sphere is an immanent offset of the center of curvature of spherical surface to the aspherical axis of the second surface. The new approach of the vignetting Field Stop Technology (V-SPOT) makes it possible to precisely record the local, meridional pitch error in the zone or at the edge of the aspherical surface and, together with the centering deviation of the vertex, to determine the aspherical axis and thus the inner centering error. A short insight into the latest application of centering measurement of double-sided aspheres from only one side using the high depth of field and the large measuring range of the V-SPOT principle is given.

Highly reflective metal coatings are essential for numerous optical elements. Established mirror coatings made of silver (Ag) and gold (Au) offer high and broadband self-reflection in the infrared (IR) spectral range but are susceptible to environmental influences and mechanical stress without suitable protective layers. In the long-wavelength spectral range, in particular, the absorption bands of these protective layers partially reduce the high mirror reflectivity again. However, the noble metal iridium (Ir) is hard, extremely dense, and thermally, mechanically, and chemically stable. Iridium provides a similarly high reflectivity in the mid (MIR) and far-infrared (FIR) spectral range, as silver and gold, and high resistance to environmental influences - even without protective layers. In this paper, the different deposition processes, as well as the optical and structural properties of iridium mirror coatings fabricated by atomic layer deposition (ALD) and by magnetron sputtering (MS), are presented and compared with each other. The complex refractive indices for ALD and MS deposited iridium mirror coatings were determined for wavelengths from 200 nm to 20 μm, complementing the existing literature values. We demonstrate that iridium mirror coatings offer a high and broadband reflectivity from the mid to far-infrared spectral range. In contrast to established – protected – silver and gold mirror coatings, the iridium coatings are environmentally durable and thermally stable up to 600°C, even without protective layers. Therefore, as an interesting mirror coating material, iridium has the potential for special applications in infrared astronomy and probably also for industrial instruments.

The production of medium to large lenses (200 - 500 mm) is becoming increasingly important against the background of the semiconductor crisis. The value of a lens increases enormously through the entire value chain. A large number of processes are necessary to achieve the final contour and quality. The grinding and polishing processes must be precisely coordinated in order to achieve all requirements. The polishing process is not always a controllable variable, since various chemical and mechanical influences come together and affect the process result. For this reason, it is important to control the grinding process. The question of how it is possible to improve the surface quality as much as possible without allowing any geometric deviations is central. The effect of different machine concepts and their advantages against the background of specific quality requirements is still unknown. Therefore, a comparison of two machine concepts and their effects on the grinding process, the component quality and the possibilities of polishing the generated surfaces will be analyzed in more detail. The focus is on the MCG500 and UPG500 machine concepts from OptoTech Optikmaschinen GmbH. The results show, that the 5-axis grinding machine MCG500 enables a high-quality grinding process, which allows to reach a PV inbetween 1.5 - 3 μm. Compared to the 4-axis machine UPG500, the MCG500 is used as a pre-grinding machine to achieve a PV of 0.4 - 1.5 μm with the help of the UPG500. In addition the, the sub surface damage is only 3 - 7 μm on the UPG500 compared to 10 - 20 μm on the MCG500. With the achieved tolerances of the UPG500, the subsequent polishing process is shortened by approx. 30% compared to the upstream grinding process by the MCG500 and at the same time the process reliability to achieve the final specifications increases.

The full aperture polishing process is a very important step in manufacturing precision optics. For this the brittle glass workpiece needs to be mounted to a specific holder in order to install the lens in the polishing machine. One very common way is to use a precision holder which is machined to the exact diameter of the lens. This precision holder is mostly made from aluminium which leads to inherent difficulties in the combination with the workpiece. The brittle glass on the hard holder surface tends to chip at the corners when not handled carefully. Also, the friction between aluminium and glass is relatively small which may lead to a relative motion in the holder and therefore scratching of the surface. Another aspect is that for each lens diameter a holder must be manufactured. Therefore, more time is needed for the preparation for the process and the efficiency of the optician’s shop decreases. At the TC-Teisnach Optik, we use a commercially available, low-priced 3D Printer in order to manufacture an additional flexible part between lens and holder. This solves the problems which stem from the encounter between two hard surfaces. The friction between holder and lens is increased and the handling is simplified, since the flexible part reduces the risk of edge chipping. Additionally, this brings the possibility to use one aluminium holder for a variety of lens diameters by exchanging the 3D printed part. With this technology a 3D printer with flexible filament acts as a useful extension of an opticians’ shop and can improve the efficiency.

This contribution addresses an alternative lithographic technique for the tailored fabrication of rotationally symmetric meso- and microscale optical components. A variable ring-shaped light distribution is created by an axicon-pair based zoom-concept and can be used for the manufacturing of single optical components and array elements as well. First, design considerations of the basic axicon system and the achievable system characteristics are discussed. In particular, minimum and maximum ring diameter depending on axicon angle variations and displacement distance of employed axicons as well as potential deviations from the telecentricity condition are considered. Additionally, further aspects concerning the system implementation are presented, e.g. the achievable resolution which is dependent on the entrance pinhole. Finally, the performance of the system is presented by demonstrating the fabrication of exemplary meso- and microscale structures.

In precision optics manufacturing metrology is of particular importance. Especially for measuring freeform optics only few technologies are available, since the complex surface shape demands a high degree of freedom from the measuring device. Hence freeform surfaces are mostly measured using expensive coordinate measuring machines. At the TC Teisnach Optik we have been working on a metrology system for variable freeform surfaces using an industrial robot. This approach is challenging, since a regular industrial robot is not designed to meet the positioning accuracy needed for measuring precision optics. In this contribution we tested the possible accuracy of the robot without the use of additional accuracy improving extensions when positioning the device under test in respect to the measuring equipment. Therefore, we used a plane lens as the specimen which the robot places respecting to a dial gauge with different orientations of the robot arm. Thus, we tested the measurement accuracy in order to see the impact of the robot orientation on the positioning accuracy.

The processing of optical components surfaces is usually performed by grinding and polishing and is characterized by an increasingly fine gradation of the ablative processing. The aim of this step is to adjust shape errors, low- and mid-spatialfrequency errors caused by the previous grinding and polishing steps. These corrective polishing processes are associated with extreme accuracy requirements and thus with high equipment, process costs and long process times. A new and costeffective approach for correction polishing is the so-called Laser Beam Figuring (LBF). By controlling the pulse duration of a highly stable CO₂ laser beam source and thus the pulse energy of each individual laser pulse, the ablation depth can be locally adjusted in a targeted manner. In this way, site-selective ablation is possible to reproducibly correct the surface of a fused silica sample or to structure it with an ablation depth of ≤ 5 nm.

The investigations carried out deal with real-time evaluation and recording of vibrations during a CNC grinding process, as well as the analysis and control of process influences on the surface quality of optical components. The experiments were carried out on a 5-axis CNC machine. At the beginning, in planar grinding experiments the present vibration is detected with state-of-the-art vibrometric and optical measurement technology from Polytec. It enables in-process recording of the process vibrations and rapid subsequent topography analysis with the aid of white light interferometry. The measurements aim is to reduce the surface deviations (roughness, mid spatials, waviness) influenced by process vibrations. By carrying out a detailed modal analysis of the CNC machine used, it is possible to detect vibrations and vibration transmissions on the machine and to derive the necessary sensor concept a nd setup. Initial in-process measurements with the aid of a fiber vibrometer showed that the vibrations detected during the grinding process correlate to a high degree with the recorded topography data. It is thus possible to find the characteristic vibrations dependent on the grinding parameters as surface structures on the components, which makes it possible to predict the surface quality produced in the process.

An established measurement system in asphere production, which is a promising approach in high precision freeform manufacturing as-well, is given by a scanning point interferometer based on a multi-wavelength approach. The scanning principle enables for a great flexibility, reduces setup time and costs, and has almost no limitations in spherical departure. Due to the absolute measurement capability, the utilized multi-wavelength approach is beneficial for segmented and interrupted surfaces, which are common apertures of modern application’s optical elements. This approach has been adapted to allow for large surface measurements of up to 850 mm in diameter with highest accuracy of down to 150 nm peak-to-valley on the maximum aperture. The combination of an optimized metrology frame setup with a unique antivibration system improves long-term stability e.g., enabling a 3σ RMSi repeatability on a hemispheric surface (with 90 kg of additional load) over 10 hours without recalibration of down to 1.7 nm only. This contribution gives a general overview of challenges when measuring complex surfaces, with a special focus on large objects and their requirements. Starting from the based scanning multi-wavelength approach, the newly developed and optimized system hardware will be highlighted, as-well as first measurement results presented. These also include consistency data for different workload e.g., simulating different tooling for the sensitive objects under test.

Mechanical abrasion is usually accepted to be the predominant mechanism during material removal of glass via grinding. However, a certain chemical reaction of the used lubricant with the glass surface as occurring during polishing can be expected. Against this background, the impact of different types of water as lubricants, tap water and distilled deionised water, on surface roughness and the degree of contamination of bound abrasive ground heavy flint glass surfaces was investigated in this contribution. It is shown that in case of distilled deionised water, notably lower surface roughness is obtained. Moreover, huge differences in the presence of hydrogen and calcium were qualitatively measured via laserinduced breakdown spectroscopy. The results indicate that the type of water, and especially its content of mineral trace elements, has a mentionable impact on the grinding process and the state of the ground surface. Smoother surfaces with a lower amount of contaminations were achieved when using distilled deionised water in the course of the grinding process. This fact is of mentionable interest for the production of optical components where usually, optically inactive surfaces remain in the ground state.