Conference Agenda

The development of optical systems has a very long tradition, and innovation in this field is accelerating. From an optical design perspective, for example, the use of free-form surfaces and adaptive optics is opening up new possibilities in the architecture and design of optical systems. One key for innovation is to understand the special features of new technologies including their limitations. We present an optical architecture using adaptive freeform optics to enable a new type of fluorescence microscopy.

Multiple researchers have explored the use of 3D printed micro-optical components as interfaces to quantum point emitters by considering different designs and configurations. Typically, these designs involve parametric structures optimized in combination with idealized point source models, which is the standard approach used in the realization of imaging systems. By restricting the light emission into a limited angular extent, small NA optical beams can be obtained. This results in an increased photon collection efficiency by centimeter-scale optical objectives in comparison to the case of bare point emitters. However, although low NA beams can be obtained in this form, this does not guarantee that the obtained field profiles will match the required spatial distribution needed for maximizing the coupling of photons into single mode fibers. In our work, we propose a different approach for maximizing such a spatial field overlap condition. In order to realize this, we rely on well-known numerical routines used in the context of illumination design tasks. Finally, we compare the obtained designs to standard parametric 3D printed based interfaces, which have been used in the context of 3D printed micro-optical interfaces to single photon sources.

In this paper, we present a highly miniaturized static projection system for integrated optical applications. Our system, which is only the size of a grain of salt, is 3D-printed using a single two-photon lithography step, enabling easy integration with photonic chips or optical fibers with high alignment accuracy and low process complexity.

Unlike conventional projection slides that use a transmission function to locally absorb or block light, our approach requires an all-transparent approach to be printable using a single transparent resist material. To achieve this, we established a partially coherent projection principle that partly directs light out of the acceptance etendue, allowing us to generate gray values across the field of view and achieve all-transparent projection slides.

Our miniaturized projection system has significant potential for various applications, including metrology, sensing, and endoscopy. We believe that our work provides a significant advancement in the field of integrated optical systems and opens up new possibilities for a wide range of applications.

In recent years, 3D machining in glass for micro-components has seen a notable boost, notably with the development of a novel optical fabrication chain. This approach uses lasers for shaping and polishing, enabling the creation of complex mini-optics efficiently.

The process begins with selective laser-induced etching (SLE) to define the optics' outer shape and surface figure. Subsequent polishing, using a "one-shot laser polishing" technique, removes imperfections and reduces roughness in a single step, achieving optical-grade smoothness.

This fabrication chain is applicable to mini-aspheres as well, enhancing their production efficiency. Additionally, it allows for wafer-level production, where multiple mini-optics are interconnected on a single glass substrate. The innovative SLE wafer-level approach optimizes heat flow during polishing, ensuring uniformity and superior optical quality.

Freeform metal optics are critical components in advanced optical systems for applications ranging from laser technology to space exploration. Accurately measuring mid-spatial-frequency roughness (MSFR) on these surfaces is essential for ensuring optimal performance and quality control. We present a cost-efficient, high-precision deflectometry system designed to meet this crucial metrology need.

Our system utilizes a novel calibration method and surface reconstruction workflow to achieve nanometer-level precision in measuring mid-spatial-frequency roughness of freeform mirrors. The key components include a low-cost, lightweight, and compact-sized camera and display. We discuss the challenges in accurately calibrating the intrinsic and extrinsic parameters. We then describe our measurement approach, which employs a combination of Gray-code and sinusoidal patterns that are observed by the camera through the reflective surface. Finally, we present our algorithm for surface reconstruction based on phase difference minimization and compare our deflectometric results with those of interferometric measurements.

Our sensor demonstrates high accuracy in characterizing MSFR while offering advantages in cost and flexibility compared to conventional techniques. The system has potential applications in autonomous production architectures for efficiently manufacturing and inspecting multiple mirror components, addressing the demand for high-quality optical elements in various industries.

Specific surface artifacts and manufacturing errors on aspheric lenses can be interpreted in different ways based on the used metrology system. We will study one example that shows ambiguity between form error and inner centration. The investigation includes common tolerancing methods in optical design and how they can cover the observed artifacts, as well as the effects the artifacts have on optical performance.

A noval concept for ccp polishing calles pp (pea puffer) of small diameter aspheres, typically << 5 mm, enables the generation of aspheres featuring shallow radii of curvatures while requiring clear apertures that are too small for most ccp polishing method's footprint diameters. The pea puffer concept enables a high quality and low cost manufacture of small aspheres in industry.

We introduce an optimization framework for ray and wave optical tomographic volumetric additive manufacturing (TVAM).

In TVAM, tomographic patterns are projected with a light modulator onto a photocurable resin from different angular directions.

Once an energy dose threshold is crossed, the resin starts polymerizing.

Current approaches assume a ray optical model for light propagation, using the Radon transform as backbone, which breaks down for small features in the region of \SI{20}{\micro\meter}.

In this work we describe how a wave optical framework allows to optically print smaller feature sizes.

The optimization framework is written in the programming language Julia and allows for high-performance optimization of ray or wave optical based patterns for volumetric additive manufacturing.

This study provides a comprehensive overview of the investigation into reducing wafer deformation during laser polishing of fused silica. The study focuses on the Twyman effect, which causes unwanted curvature in thin plates subjected to surface treatment. Through careful analysis and experimentation, a strategy for minimising stress-induced deformation is proposed.

Photopolymerization is a light-based additive manufacturing (AM) technique that facilitates the fabrication of complex three-dimensional (3D) structures quickly and cost-effectively. One-photon polymerization allows printing with high speed despite its limited resolution. In contrast, two-photon polymerization (2PP) offers high precision and resolution but requires longer printing times. We propose a method combining 2PP and one-photon absorption (1PA) to get advantages of the dual capabilities, allowing for faster printing while preserving high resolution and enhancing depth sectioning. In this study, we employ a blue light to pre-excite a photocurable resin for rapidly reaching the polymerization threshold by 1PA and a precisely focused femtosecond beam to provide the missing energy for surpassing the threshold and solidifying the resin through two-photon absorption. First, we investigate the impact of the pre-sensitization by a blue light illumination on 2PP, demonstrating two orders of magnitude reduction in light dose. After that, we introduce a custom 3D printer utilizing blue light sensitization in a light-sheet mode on 2PP, which accelerates polymerization onset and improves surface quality.

Zoom lens design can be particularly challenging because the aberrations of the lens groups change as the lens zooms. The changes of the third order aberrations of each lens group between the zoom configurations are related through stop and conjugate shift theory and can be quantified once the residual aberrations of the lens groups are known at just one zoom configuration. By applying stop and conjugate shift theory to examples from patent literature, we establish some basic principles of third order aberration balancing in zoom lenses design. These principles are then applied to existing designs and are used to guide a computational method for planning the aberration balance of a zoom lens.

Since the development of the first achromatic lenses back in the 18th century, dispersion models have been constant companions of optical designers. Usually glass properties are described by Abbe numbers and partial dispersions, and color correction is explained and visualized e.g. with Pg,F- and Herzberger diagrams. We have recently developed an alternative approach to color analysis and color correction based on principal component analysis (PCA) of normalized refractive index data. Unlike their traditional counterparts, the resulting diagrams can be used not only for glass selection, but also for a quantitative prediction of partial refractive powers and residual color aberrations, which arise naturally from the PCA. The method can easily be transferred to any spectral range and set of glasses, as it is intrinsically model-free and does not involve any choice of reference wavelengths or tuning of parameters. We present application examples of the method and discuss the impact of using different glass catalogs and wavelength samplings.

Mechanical and thermal disturbances in optical systems are attracting increasing attention as accuracy requirements rise. For this reason, it is necessary to consider these disturbances at an early stage in the design process. This can be done by a holistic multiphysical opto-thermo-mechanical simulation. Such an approach is presented with a focus on efficient thermomechanical computation through a quasi-static approximation.

A new approach for glass substitution in the lens system optimization process has been developed. Exploring existing longitudinal aberration contributions, the new method uses sensitivity analysis to find optimal optical glass constants (refractive index, Abbe number, and relative partial dispersion) for certain optical system elements. A case study introducing the glass substitution method to the optical system design is described. It is shown that the new approach provides step-by-step improvements in the optical system’s longitudinal aberration correction.

The high cost of optical raw materials in the long wavelength infrared (LWIR) region necessitates the development of cost-effective solutions without compromising resolution. Chalcogenide glasses offer a faster and easier production process compared to growing single crystals of Germanium (Ge). Additionally, they can be molded into complex optical surfaces, reducing processing costs further for serial production. In this study, we explore the potential of chalcogenide lenses. Our comprehensive design study demonstrates that chalcogenide lens designs can achieve comparable or even superior optical performance with reasonable system complexity when compared to a wide-angle benchmark Ge design.

Computer scientists discovered that a school of Italian landscape painters in the 18th century around Giovanni Paolo Panini (1691 - 1765) did not paint their paintings in rectilinear perspective, but in an alternative, non-rotationally symmetrical perspective projection. For three-dimensional landscapes with large fields of view, Panini’s projection provides much better images. Recently, it has been widely used in 3D computer graphics software and game engines. However, this alternative perspective projection is still unknown in the optics community.

We present first optical designs of imaging systems with Panini projection. The use of toric or free-form surfaces is very advantageous for this type of system. We discuss the pros and cons of hardware and digital post-processing solutions as well as a design example that benefits from a digital co-optimization strategy.

Analytical expressions for the ray-transfer matrix have been proven useful for the understanding of ray propagation in gradient-index (GRIN) lenses. The determination of an exact analytical expression for the ray-transfer matrix of arbitrary GRIN lenses remains unsolved. We propose an approximation based on the perturbation method with highly accurate results for models of the crystalline lens, which outperforms existing methods.

The fast computation of the Jacobian is an essential part in the optimization of optical systems using the damped least-squares algorithm. While finite differences provide an intuitive way to approximate derivatives, algorithmic differentiation is a technique to calculate them exactly. However, applying algorithmic differentiation to a raytracing routine for optical systems with many parameters is comparatively expensive, where the main costs are caused by the determination of a ray-surface intersection. To overcome this disadvantage, we present a mathematical analysis of the ray-surface intersection and its efficient differentiation in both forward and reverse mode algorithmic differentiation. Futhermore, the structure of the optimization variables and operands is exploited to derive a method that allows to compute the Jacobian in the same order of computational complexity as the primal raytrace. The method is successfully tested for a freeform design task and a classical spherical lens system.

OptiMat, by Sagittal Optics, is a tool developed to generate initial designs for color-corrected lens-based systems. OptiMat focuses on material selection, which is the most critical aspect for correcting chromatic aberration. However, this tool extends beyond material selection; it is also used to establish initial systems in the design process, which optical designers can further refine. By selecting from a catalog of materials and specifying the number of lenses in the system, optical designers receive the ideal combination of materials to correct chromatic aberration, together with a set of parameters to further improve the received system, such as lens ordering and radii. Additionally, engineers can filter combinations based on different metrics, such as chromatic and monochromatic aberrations.

In optical system design, material selection is not usually decided at the start of the project. Instead, it is determined gradually through a merit function that explores numerous combinations, which is an inefficient method. OptiMat identifies the best material combination upfront, drastically reducing design times from months to hours.

In this contribution, the results achieved through OptiMat will be presented alongside case study outcomes and detailed comparisons with other tools. This will highlight the significant advantages offered by OptiMat in optimizing lens-based systems.

Accurate and uniform fabrication of microstructures on highly curved substrates requires exposure with the waist of a focused laser beam at every point. In order to realize this, the exposure beam must be held perpendicular and focused onto the local substrate. Here we present an optical tool for our developed 5-axis nano-positioning and nano-measurement machine based on the chromatic differential confocal microscope.

In the realm of astronomical scientific exploration, deployable and scalable approaches in space telescope systems are reshaping our understanding of the universe. Two revolutionary membrane-based space telescope designs, on-axis OASIS (Orbiting Astronomical Satellite for Investigating Stellar Systems) and off-axis SALTUS (Single Aperture Large Telescope for Universe Studies), have been developed as mid/far-infrared telescope concepts featuring an inflatable primary mirror. Through the scalable primary aperture design, these deployable space telescopes leverage an all-encompassing optical architecture that taps into the uncharted potential of extremely large telescope apertures. These visionary mission and optical designs pave the way for the next generation scalable telescopes of unprecedented dimensions and diffraction-limited imaging resolutions.

We present a mesh-based method for optimizing double-sided freeform lenses to control their caustic effects. Unlike traditional single-sided approaches, we optimize both sides of the lens simultaneously, using a bijective correspondence between the two sides to control light refraction paths. Our approach balances image fidelity, geometric compatibility, and physical constraints. Results demonstrate the method's capability to accurately produce intricate light patterns, opening new possibilities in optical applications.

We discuss an inverse method to compute a freeform two-reflector two-target system. The optical path length constitutes an integral component and can be expressed in terms of position coordinates at the first target. The system is expressed in terms of a generating function, closed with energy balance and requires a sophisticated least-squares solver to compute the shapes of the reflectors. In a numerical example, we illustrate the algorithm's capabilities to tackle even the most intricate light distributions.

The use of beam-based technologies to process optical elements with nanoscale precision enables the fabrication of freeform surfaces. In particular, atmospheric pressure plasma jets (APPJs) have desirable properties, e.g., depth precision < 5 nm, low surface roughness and processing at atmospheric conditions. However, the composition of optical glasses and glass ceramics, containing metal oxides, leads to the formation of non-volatile reaction products that remain on the substrate surface. These residues reduce the etching rate and cause severe roughening of the surface. Laser irradiation has already been demonstrated as a promising option for removing the residual layer and the aim of the current work is to integrate it into the APPJ system for simultaneous processing. Therefore, an excimer laser (λ = 248 nm; tPulse = 20 ns) with a maximum pulse frequency of 100 Hz was added to a plasma jet setup and experiments with varying laser fluences as well as laser frequencies were performed on N-BK7 substrates. White light interferometry was used to analyse the samples. The experiments showed an improved etching result with higher removal rates for the combined process at high laser pulse frequency (100 Hz) and fluences in the range of 0.1-0.45 J·cm-2.

The manufacturing of optical components is subject to constant efforts to optimise production processes in order to achieve high surface qualities under the most economical conditions possible. This includes the refinement of existing technologies or development of completely new production technologies. One possible approach is the combination of conventional machining processes for optical components like diamond turning, grinding or polishing with laser-based processes to thermally influence the surface for improved machining or surface properties. For this, knowledge of the thermal interactions of the laser on the component surface is needed, which in turn requires its metrological acquisition. In this work, measurements were carried out using various methods for the controlled heating of glass surfaces by an infrared laser (λ=1070 nm). Among other things, a clear correlation between the samples surface roughness and the laser absorption is found.

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Mechanical cracks induced during grinding of brittle materials known as subsurface damage (SSD) reduce mechanical and optical properties of optical components. A characterisation of SSD is needed to guarantee a good quality and to optimize individual processes and processing chains. Current research focuses on non-destructive methods such as optical coherence tomography (OCT) to evaluate SSD depth and distribution and to replace currently established, but time-consuming and labour-intensive destructive methods. Yet the imaging of SSD remains challenging, even with high-resolution OCT providing a high sensitivity. The presented work proposes a combined measurement approach of enhanced SSD imaging by using a potassium hydroxide (KOH) wet etching process prior to OCT measurement. An etching process using 30% KOH at 80°C is applied and resulting etching rates are analysed. It is shown by an iterative etching experiment on optical glass SF6 that the KOH etching process enhances OCT signals of SSD under the surface, revealing up to 2.4-times deeper maximum SSD depths using an identical measurement setup.

Nowadays, more and more complex optical elements are used in optical applications, but this can lead to high costs, a time-consuming manufacturing process and limited availability of unconventional elements. Therefore, in this work, we propose LCD 3D printing as alternative cost-effective technique, which is not only user-friendly but also free from design constrains and enables the fabrication of free-form optics. The tested polymeric materials showed promising results for printed optics and optical applications. In addition, 3D printed optical elements were evaluated in terms of their suitability in selected applications with opto-chemical sensors and imaging techniques, with results comparable to those obtained with the corresponding glass optical elements.

Light scattering in optical systems is caused by various imperfections such as surface roughness, bulk inhomogeneity, contamination, and ghost light beam paths. Control of these scattering sources is crucial, particularly for high-precision optical components, and involves both measurement and modelling from the design phase through fabrication to system integration. Recent developments at Fraunhofer IOF have led to advanced instruments for characterization of both optical components and system. Moreover Light scattering measurements provide not only analysis capabilities but also critical data for optimizing fabrication processes by identifying scattering contributors. Results and applications of these techniques and tools will be presented, highlighting their impact on optimizing optical system fabrication.

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. 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.

On December 5, 2022, Lawrence Livermore National Laboratory’s (LLNL) National Ignition Facility (NIF) made history, demonstrating fusion ignition for the first time in a laboratory setting. NIF produced 3.15 megajoules (MJ) of fusion energy output using 2.05 MJ of laser energy delivered to the target, demonstrating the fundamental science basis for inertial fusion energy. In this presentation, the major large optic technology advancements that have enabled NIF today to routinely operate at now 2.2MJ, further aiding ignition experiments, are discussed. In addition, latest developments on fabrication processing science to aid in fabricating complex freeform optics with high precision for use in various laser systems are discussed.

U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-XXXXX

The laser-induced damage resistance of large optical components remains an important limitation for the maintenance costs, reliability, and further development of high energy/high-power (HE/HP) laser systems. With numerous manufacturers providing different laser-induced damage threshold (LIDT) values in the nanosecond regime, a simple ranking based on numbers alone may not provide a clear picture of the best choice. Variations in testing procedures, albeit following the ISO 21254 standard, further complicate the selection process. By employing a comprehensive 1-on-1 test procedure, it becomes possible to observe various parameters that influence LIDT values. An overview on how the laser beam size, the spectral characteristics of the tested optic and possible contamination of the surface are influencing the LIDT values will be presented.

The performance of an optical component or surface might quicky be limited by light scattering induced by the surface and coating roughness, as well as imperfections and contaminations. On the other hand, the scattered light contains valuable information about its source, which makes scattering based techniques powerful characterization tools for these important features. A major advantage is the fast, robust, and contact free measurement approach enabling even close-to process applications. Based on several examples we demonstrate the potential of light scattering characterization during the fabrication process up to even in-situ coating inspection.

NSOS-alpha is a 1.5-m aperture, F/1.55, wide field prime focus telescope for the Korea Astronomy & Space Science Institute (KASI) to discover and catalogue near-Earth asteroids, especially Potentially Hazardous Asteroids. Among the different optical designs, the current baseline is based onto a design with reduced sensitivities to both manufacturing and alignment tolerances, to optimize as-built performances instead of reducing nominal aberrations only. Different optimization techniques have been used and compared. As result, a fast and effective optimization procedure has been identified and implemented, and it will be used also during the manufacturing process to improve overall performance.

The flexible and efficient production of precise optical free-form surfaces requires advanced kinematic operating principles. Due to the complex surface geometries, polishing processes with point or linear contact are used. These generally result in longer polishing times due to the smaller footprint compared to large-area polishing tools. The creation of a high precision, polishable surface in the shaping steps of the process chain is therefore of great importance. This applies in particular to minimising the roughness, but also the depth of SSD (sub-surface damage) and the mid-spatial frequency errors before the polishing process. The article describes selected process chains for the production of free-form optics and presents options for optimising the required polishing steps.

A new concept for polishing pads for flat and spherical surfaces is introduced which comprises additive manufactured polishing pads made of cerium oxide. By using additive manufacturing technologies in polishing processes with polishing slurry, those processes can be substituted with tools containing bonded grain. The bonded polishing pads can be fabricated using rolling processes. The pad geometries can be adjusted by using laser cutting. Furthermore, surface modifications of the pad can be applied with laser processes as well to favour quality and economic factors of polishing processes. First results from the experimental setup are showing, that lapped surface with a roughness Rq of ~500 nm can be polished to approx. 30 nm roughness Rq by polishing with pads using bonded grain cerium oxide foils.

Different Light-based techniques for 3D printing have been developed such as SLA and DLP that use single photon absorption and direct writing by scanning a focused spot using two photon absorption. These techniques employ a layered approach using incoherent imaging. Herein, we propose a layerless approach using coherent holographic projection which is based on Tomographic Volumetric Additive Manufacturing (TVAM). We demonstrated this concept by implementing a volumetric printer using a Digital Micromirror Device (DMD) in a Fourier configuration and showing its capabilities by printing a micrometric scale object. The use of the Lee holograms method allows us to use the DMD as a fast phase modulator, and the combination of tiling holograms with Point Spread Function (PSF) modifications allows us to reduce speckle noise and provide three-dimensional control of the projections. We use these holographic projections to fabricate millimetric 3D objects in less than a minute.

We here present our research into application-adapted laser beam shaping which enables the generation of tailored light volumes, explicit optimization of the temperature distribution within a work piece and high-fidelity beam shaping in combination with optical amplifiers.