This PDF file contains the front matter associated with SPIE Proceedings Volume POM20, including the Title Page, Copyright information, and Table of Contents.

The continuing trend towards lightweight construction and the associated machining rates of up to 95 % lead to an increased use of high-performance materials. The ever growing demands on the strength and quality of components and the associated use of materials which are hard to machine require the further development of new, economical machining techniques. In ultrasonic-assisted machining, an additional high-frequency vibration is superimposed on the conventional machining process. The vibration of the tool is usually excited axially or longitudinally to the workpiece, i.e. vertical to the cutting direction. An additional vibration overlay around the rotation axis (torsional) of the tool is also possible. This generates a vibration overlay in the cutting direction. The vibration initiation causes vibration amplitudes in the range of a few micrometers at the tool cutting edge. This leads in turn to a high-frequency change in the cutting speed or feed rate. Overall, an additional torsional vibration overlap can further reduce cutting forces, increase tool life and improve workpiece quality. In order for a grinding tool to generate a torsional vibration, a special tool was required that had to be designed by simulation. The formation of a torsional vibration was achieved by helical slots in the sonotrode. Depending on the angle of rotation and the length of the slots, a part of the axial vibration is converted into a torsional vibration by an axial excitation of the sonotrode. The aim in designing the slots was to achieve the highest possible vibration amplitude. Following the simulation, the slots were inserted into the tool in the corresponding optimum geometric position. Afterwards, the specially designed grinding tool was validated by machining the brittle-hard glass-ceramic material Zerodur. The first test results with the torsionally vibrating tool are presented in the following.

We report on a photonic process chain to manufacture optical elements by non-contact all laser based micro-processing. Firstly, pre-defined optics geometries are generated by high-precision 1030 nm femtosecond layer-by-layer ablation. In order to meet high surface quality requirements, inevitable stipulated for optical use, the surface of thus generated elements has to be smoothened by subsequent 10.6 μm CO₂ laser polishing. To demonstrate this surface finishing process, a complex optic geometry i.e. an axicon array consisting of 37 individual axicons is fabricated within 23 minutes while the polishing shows a reduction of the surface roughness from 0.36 μm to 48 nm. The functionality of the fabricated optic is tested using the 1030 nm wavelength ultrashort pulsed laser. Several sub-Bessel beams exhibiting the typical zeroth-order Bessel beam intensity distribution are observed, in turn confirming the applied manufacturing process to be well applicable for the fabrication of complex optic geometries. Cross sections of the quasi-Bessel beam at the axicon in the middle of the array in both, x- and y-direction, show an almost identical intensity profile, indicating the high contour accuracy of the axicon. Detailed investigations of the axicon in the middle of the array show a tip rounding of 1.37 mm while the sub-beam behind this axicon is measured to have a diameter of 9.5 μm (FWHM) and a Bessel range in propagation direction of 8.0 mm (FWHM).

The form generation of optical surfaces by grinding and mechanical polishing results in small sub surface damages in the form of micro cracks that conventionally have to be removed by further removal of the damaged surface layers. In order to reduce process time and material cost non-ablative methods for removal of micro cracks are desired. Utilising the low optical penetration depths of less than 10 μm for CO₂-laser radiation in glass, the laser energy can be used to heat up and melt thin surface layers. Using a 1.5 kW CO₂-laser, a quasi-line focus formed by a scanner unit and a constant feed speed, it is possible to close all micro cracks present in the rough grinded test surfaces (max. SSD-depth ~ 63 μm), while achieving a process time of less than 2 seconds for a Ø 30 mm N-BK7 lens, respectively 7.5 seconds for fused silica. With a Sa as low as 50 nm and low distortion from the original shape the surfaces can directly be conventionally polished, further reducing the process chain complexity.

The production of complex shaped optical elements like non-standard aspheres, acylinders, or freeform elements are highly demanded. Thus, optical manufacturing technologies need to be developed for optical systems to design freeform surfaces. Reactive Plasma Jet (RPJ) is one of the most promising tools for freeform generation of fused silica, SiC, ULE® and silicon. However, there are severe limitations when this technique is used for the surface machining of optical glasses like N-BK7®. The chemical interaction between plasma generated active species and metal components of N-BK7 induces the formation of a residual layer in the plasma-surface contact zone and surrounding which can degrade the capability of acquiring the required surface profile. It is shown that elevated surface temperature can modify the residual layer leading to higher predictability of freeform machining results.

In this article a new way of fabricating micro-optics, especially micro lens arrays (MLA’s) with lens heights up to several hundreds of micrometers is shown. Existing methods of MLA fabrication are compared to the new approach. Also applications are presented. A novel short pulse CO₂-laser system is used for the production, which allows pulse lengths down to 200 ns. In combination with a common galvo-scanner system, the micro lenses are preformed by an ablation process in tens of seconds. Here, different lens diameters, lens radii and array sizes can be produced. In a second step, the MLA is fire-polished with the same laser source. For this process step the laser is switched to cw-mode. The preformed lenses melt and get a defined radius as a result of the surface tension of the molten glass. Measurements of the resulting geometry are be presented. As the results show, the laser based micro lens array fabrication process has a high reproducibility, very high flexibility, short process times and can process different glasses like borosilicate, soda lime or fused silica.

Nanometer resolution metrology is a significant topic in the development and production of complex shaped high precision optics. The Nanopositioning and Nanomeasuring Machine NPMM-200 at ITO is built for nanometer scale positioning in a large scale measurement volume of 200 mm x 200 mm x 25 mm. The concept of the machine is based on a high precision interferometrically controlled stage in a stable metrological frame made of glass-ceramic. In this frame, different types of sensors can be attached for measurement of surface topographies. In this contribution, we present the use of optical sensors, such as a fixed focus probe, for measuring of high precision aspheric and freeform optics with this new machine.

Large optics with diameters of up to 1.5 m are being used more and more in industry and science. Flatness measurements of these optics are needed with uncertainties down to a few ten nanometres. For slightly curved specimens with radii of curvature down to 10 m uncertainties in the sub-micrometre range are required. We are currently building a new form measurement system which aims to fulfil these requirements. It will be set up in 2020 and the first measurements will be carried out in 2021. The setup can be operated with different sensor heads which use deflectometric- or interferometricbased methods. We plan, amongst other things, to use Fizeau interferometers with aperture sizes of 10 mm, 100 mm and 150 mm. The mechanical and optical setup of this new system is presented and simulation results of conventional subaperture stitching methods for this system with an aperture of 100 mm are shown. We also discuss the different measurement methods for the absolute form measurement of these optics.

The aim of our research was to study middle spatial frequency errors (MSFE) on optical surfaces. We investigate the surfaces after manufacturing processes to find out the main affecting factors and to choose the proper processing parameters to minimize the size of the errors. To find an appropriate parameter window we have to be able not only to define the factors, which lead to MSFE, but also to analyze the change of the error after next following production steps.

When developing optical systems, every element within the light path is considered in technical optics. In ophthalmic optics, however, spectacle lenses are usually designed to provide a given optical power at a position called vertex sphere, ignoring the actual imaging processing inside the eye. We have developed a novel technology (trade name DNEye® PRO) overcoming this practice. The computation of the wavefronts does not stop at the back surface of the spectacle lens but is continued right into the eye through its refracting surfaces. The assessment no longer takes place at the vertex sphere, but at the retina. This calculation is based on individual measurements of biometrical parameters of the eye and comprises the complex shapes of the wavefronts and of the refracting surfaces including their higher-order components. As a result, effects which arise from the individual structure of the eye and its components are considered giving rise to sharper imaging and better design retention.

At Deggendorf Institute of Technology a student project is currently under way to build a Stevick-Paul telescope for astrophotography. An important step in the overall development procedure of each telescope is the design of a beam-path and ensuring its suitability under optical and engineering aspects. The students performed this process in a sequential manner by using several different computer programs (e.g. MATLAB, Zemax, Creo Parametric). To accelerate the beam path design process, a Python program to automate the major part of the design process with minimum human supervision was created. The input data of the python program consists of ranges of the desired characteristics of the Stevick-Paul telescope, such as focal lengths, primary mirror diameters and tilts etc., mirror thickness and mount geometries, as well as the specific type of camera. After setting the input, the program creates 2D cross-sections of beam paths according to the formulas of D. Stevick and may introduce a flat fold mirror to reduce the overall system size as well as improve the accessibility of the focus plane. The subsequent assessment routine checks against the susceptibility for stray light and performs a complex analysis of the available installation space to ensure sufficient mechanical tolerances. In this way, collisions between mirrors, mounts and cameras are avoided and obstructions of the beam path are prevented. At any stage, the program can produce graphical representations of the beam paths. In this paper the computer-aided design of a telescope beam path with a focal length of 2400 mm is demonstrated. During development of the software, a subset of folded Stevick-Paul telescopes, in which certain components are parallel, was found. This subset may be useful to simplify the alignment procedure. In conclusion, further refinement of the software is necessary, although the program is already a useful aid for certain aspects when creating a beam path design.

During the development of an optical system, one comes to the point where you have to build the optically active element into a mechanical device that becomes part of the system. At this point you come across the well-known question that it is not only necessary to consider and ensure the quality of the individual element. It is also important to look at the entire component in order to identify potential influencing factors on the performance of the optical system. At the beginning of a two-year project at Technologiecampus Teisnach the polishing process of a nonlinear crystal as the crucial component of the optical system was being explored. This system is designed to create continuous wave laser beams in the deep UV range. The crystal has to be embedded between two prisms. Roughness and shape of the crystal is ensured via the polishing process which alone has many influencing factors and was examined at the beginning of the project. The quality of the crystal can be as good as it can be, but if the contacting prisms do not fit, the whole prism-coupled device will become unusable in the overall optical laser system. The performance of the laser can only be achieved by harmonizing all elements of the PCD and the PCD itself into the laser set-up. In the current phase of the project this question will be dealt with. The prism-coupled device is split up into its individual parts, which are the nonlinear crystal, the prisms as optical auxiliary components, micro screws and mechanical support. Going through the requirements to the properties of the crystal and their limitations, the influence of the PCD on the optical performance of the crystal is presented. Here, the main focus is placed on the mode of fixing the crystal between the prisms and on putting the stack of crystal and prisms in the laser beam. The influencing factors between the crystal, the prisms and the method of fixing the PCD are described.

Finishing of optical components is one of the main challenging tasks in optics manufacturing. This includes precision polishing, smoothing, and surface modification, e.g. for subsequent contact bonding. Recent developments have shown that the use of dielectric barrier discharge plasmas at atmospheric pressure allows for the conception and realization of novel approaches for such surface finishing. Since this type of plasma stands out due a low gas temperature, it is also referred to as “cold” plasma. It is thus suitable for the treatment of temperature-sensitive optical media. In this contribution, selected applications of such plasmas in optics manufacturing are presented. First, it is shown that precision polishing of different optical media can be achieved by the use of direct plasma discharges with an inert process gas. By the plasma-induced selective removal of roughness peaks, a notable decrease in surface roughness of the initial value was obtained. Second, plasma-induced cleaning of optics surfaces including the underlying plasma-physical and plasmachemical mechanisms is presented. Here, not only surface-adherent carbonaceous contaminations, but also residues from polishing agents and other operating materials can be removed. Such cleaning results in several advantageous effects as for example an increase in laser-induced damage threshold or a modification in free surface energy, leading to an improved adhesion of coatings and cements. Finally, plasma treatment is suitable for refractive index matching of glass surfaces by a plasma-induced modification of the chemical composition of the near-surface glass layer.

This research is focused on the link between manufacturing parameters and the resulting mid-spatial frequency error in the manufacturing process of precision optics. The goal is to understand the generation mechanisms of mid-spatial frequency errors and avoid their appearance in the manufacturing process. Also, a simulation which is able to predict the resulting mid spatial frequency error from a manufacturing process is desired.

Due to the advantages over conventional polishing strategies, polishing with non-Newtonian fluids are state of the art in precision shape correction of precision optical glass surfaces. The viscosity of such fluids is not constant since it changes as a function of shear rate and time. An example is during the shape correction by polishing with pitch or ice, where pitch flows slowly under its own weight and acts like a solid body during short periods of stress as its viscosity increases. One approach is to use thixotropic fluids like ketchup to reduce the roughness by polishing, without changing the shape of the sample. Tomato ketchup shows a time-dependent change in viscosity: the longer the ketchup undergoes shear stress, the lower is its viscosity. Therefore, in this article, a new processing is put forward to polishing glass surfaces with ketchup containing micro-sized Ce₂O. Besides conventional ketchup, curry ketchup and an organic product were tested as well. An industrial robot onto the work piece surface guides the polishing head. The different types of ketchup are compared by means of roughness and shape accuracy and the potential regarding to manufacture high-precise optical glass surfaces.

The developed concept represents a universally applicable clamping system designed to fit in any measuring machine with any measuring principle. The design ensures that, as long as the lens remains clamped, the measurement results are reproducible. Form errors due to tension remain constant across all measuring and processing steps. The version presented in this paper was developed especially for small lenses in the diameter range up to 40 mm. On the one hand, the design allows for fast measurement of loose lenses. On the other hand, the device can also be used for measurement comparisons, since lenses can also be mounted permanently. In the following, the concept and first results of measurement tests are presented.

The Preston-equation implies, that, besides the relative speed υ_rel and a specific constant K_P, the pressure p plays a significant role for the removal rate when polishing an optical component. This paper demonstrates a possibility for a qualitative evaluation of the pressure distribution before the polishing process. A pressure-sensitive foil is used as a gauge for pressure measurement. The effectiveness of this measuring method is explained. Specific weaknesses and limitations in the use of these foils are discussed. A method for an integrated evaluation of the pressure on different spots of the polishing pad is proposed at the end of the paper.

Manufacturing precision optics is a complex process chain, which requires many operations on different machines. This is combined with operator-dependent steps such as manual cleaning, loading and measuring. In order to realize this process chain on a smaller shop area and to achieve a higher level of automation we build an operator-independent polishing cell. In this cell, an ABB robot serves as the actuator handling the workpiece. We positioned the robot in the center of the polishing cell to operate several workstations, so the whole process chain works with one single actuator. This arrangement allows a smaller and cheaper system, since no additional handling is required.

The quality of optical components such as lenses or mirrors can be described by shape errors and surface roughness. With increasing optic sizes, the stability of the polishing process becomes more and more important. If not empirically known, the optical surface must be measured after each polishing step. One approach is to mount sensors on the polishing head in order to measure process relevant quantities. On the basis of these data, Machine Learning algorithms can be applied for surface value prediction. The aim of this work is the stepwise development of an artificial neural network (ANN) in order to improve the accuracy of the models' prediction. The ANN is developed in the Python programming language using the Keras deep learning library. Beginning with simple network architecture and common training parameters. The model will then be optimized step-by-step through the implementation of different methods and Hyperparameter optimization (HPO). Data, which is generated by the sensor-integrated glass polishing head, is used to train the ANN-model. A representative part of these data is held back before, in order to validate the models' prediction. The so-called dataset contains measured values from multiple polishing runs, preceded by a design of experiment. After the model is trained on the dataset, it is able to predict the result of not yet performed polishing runs, with given polishing parameters. Concrete, the ANN is used to predict the resulting glass-surface quality, which includes the surface roughness and the shape accuracy, calculated by the material removal over time. The prediction by artificial neural networks reduces the polishing iterations and thus the production time.