This PDF file contains the front matter associated with SPIE Proceedings Volume 12755, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The manufacturing of optical freeform surfaces offers a high potential for optical approaches in the future, since they can make new optical systems lighter and more compact or even enable completely new functions, compared to conventional optics. However, the expanded possibilities go hand in hand with higher complexity in production of freeforms for precision optical applications. This leads to high prices and long delivery times. This paper shows an approach to improve manufacturing of freeforms in small batch sizes with a high degree of customization, by a process chain consisting of (ultrasonic-assisted) pre- and fine grinding combined with ultra-fine grinding using resin bond tools. The process chain is suited for efficient fabrication of optical surfaces. A main focus of the experiments is on reduction of low- and mid-spatial frequency surface deviations, as well as surface roughness. Several different influencing factors in a 5-axis CNC grinding process of fused silica freeforms are investigated and their effects on the resulting surface topography (from the low to the high frequency range of surface deviations) are observed using white light interferometry measurement principles. Various optimization approaches can be concluded.

Cryogenic machining is a cooling strategy that has recently been frequently found in research in machining processes for materials such as inconel or titanium. In particular it is reported that these processes are more efficient in terms of tool life and material removal rate compared to those with water-based cooling lubrication. An increase in efficiency and productivity has significant potential from a cost perspective, especially when grinding Ceramic Matrix Composite materials and similar. These processes are used, for example, in the lightweighting of telescope mirrors made of e.g. fiber-reinforced silicon carbide, or Zerodur. An increase in productivity would be clearly noticeable in the manufacturing costs due to normally long machining times. In the "KryoSonic" project, we investigated whether and to what extent the use of cryogenic machining affects the rough machining of Zerodur with and without ultrasonic support.

Plasma jet polishing of ground freeform optics is presented. Accurate measurement of local maximum surface temperature and a closed-loop for temperature-based power control is necessary to achieve form-preserving uniform surface polishing. Microroughness can be significantly reduced in one step. The roughness after plasma jet polishing in higher spatial frequencies strongly depends on the extend of sub-surface damage and grinding marks.

The demand for precision glass optics with complex shapes has increased in recent years, primarily in sectors such as lighting technology, automotive, laser technology, and consumer electronics. This rising trend, combined with production costs, represents a major challenge for the industry as demand needs to be met in a cost-effective manner. To address this challenge, the industry had developed innovative solutions to remain competitive. Precision glass molding (PGM) has emerged as a promising solution for this purpose. PGM is a replicative manufacturing process that enables a cost-effective production of precise glass optics. In this process, a glass preform is heated up into a viscoelastic state and pressed between a pair of molding tools. However, the manufacturing process of the molding tools can be both time-consuming and expensive. Additionally, they are specifically manufactured to produce a certain lens design under a given set of molding parameters. During this investigation, we considered a molding tool pair used to produce a specific lens design. We varied the process parameters, such as pressing force and temperature, into several different combinations, and produced the lenses subsequently. The aim is to analyze the flexibility in the PGM process, and to determine whether different lens geometries can be produced with a pair of molding tools. The final shape of the molded lenses was measured using a profilometer, while the center thickness of the lenses was measured with an absolute digital measuring probe. Finally, the shapes obtained from the molded lenses were compared and analyzed. The pressing temperature and force have a considerable impact in the final shape, which can be tuned along with other process parameters to achieve a certain degree of flexibility in the molding process.

Fibre optics for demanding applications in communications, metrology, laser technology and medicine play an important role in today’s world. Thus, efficient manufacturing technologies to machine silica preforms, being the predominant material, are required. Ultrasonic-assisted drilling using diamond grinding tools is a very efficient and highly economical machining technology. In addition to significantly lower process forces and a longer tool life, there is less surface damage to the glass fibre preform. Besides the pure drilling process, also the alignment of the channels to a core fibre using automated camera systems is important to improve the overall productivity. Present developments of ultrasonic-assisted machining processes for preforms will be presented. An overall overview on ultrasonic drilling processes also for other applications will be given.

Miniaturized lenses are increasingly utilized in a range of applications, including medical devices, optical communication, and imaging systems. The characterization of these lenses is crucial as their performance is highly dependent on their geometrical and functional properties. However, the small size of these lenses coupled with the required short measurement times, presents a significant challenge for conventional measurement techniques. Recent advances in optical coherence tomography (OCT) and Shack Hartmann wavefront sensors (SHWS) have enabled rapid, semi-automated geometric and functional characterization of miniaturized lenses when appropriate hardware, software, and algorithms are integrated. OCT is a non-invasive imaging technique that can provide high-resolution cross-sectional images of the lens, allowing the accurate measurement of its central thickness, curvature, and other geometric parameters of both surfaces. Moreover, SHWS can be used to measure the transmitted wavefront error of the lens, which is directly related to its optical performance. In this paper, we demonstrate the use of OCT and SHWS to characterize polymer and glass lenses with diameters and thicknesses of a few millimeters with spherical and aspherical shapes. Our results show that OCT is capable of accurately measuring the central thickness and surface profile of the lenses, while SHWS provides information on their wavefront aberrations. By combining these two techniques, we were able to obtain a com-prehensive characterization of the lenses' geometrical and functional properties.

Acoustic emissions (AEs) are elastic stress waves in solids. They occur when irreversible changes take place in the internal structure (e. g. the formation of cracks) of a solid (material). The benefits of the measurement of AEs are well known, and their application has already been described for various use cases. They are, for example, used for monitoring bridges to detect rope cracks. We want to investigate the possibilities of using AEs in the polishing process of glass, a complicated manufacturing process with several overlapping, chemical and mechanical influences. We will present the results of preliminary studies which shall answer the following questions: • Is it possible to measure acoustic emission signals, even if an unhindered access to the place of origin under manufacturing situations can not be guaranteed? • How is the development of the signal during the polishing process? • How can acoustic emissions be used in the future to improve optics manufacturing? • Is the opportunity of an endpoint detection existing? Answering these questions will demonstrate the abilities AEs can offer for evaluating and monitoring manufacturing processes. In the future it should be possible to create a cyber-physical system (CPS). In such a system, AE signals can be merged with other sensor signals (e. g. power of the machine, pH value, · · ·).

For the design of a new asphere measuring system, it is necessary to know transmission values for a system consisting of a source, an optional auxiliary filter and an optical filter, on which angle-tuning is performed. To generate these transmission values for different angles of incidence and polarizations a simulation program was created. Input data of the simulation were based on data provided by the manufacturers. Simulation results are presented for a sample of four systems. Simulation was deemed successful and accelerates the design process of the metrology system, since a large range of source and filter combinations can be evaluated swiftly. Limitations of the simulation are discussed as well.

In addition to reducing paper consumption, paperless production offers the possibility of automating further work steps and additionally gaining further process information in the production of ophthalmic lenes.