Optical Fabrication and Testing IX

To further improve the sensitivity of the laser interferometers detecting gravitationnal waves one strategy is to increase the optical power circulating inside the kilometers long arm Fabry-Perot cavities. Next generation of gravitational wave detectors, aims to achieve optical power in the order of the Megawatt incident on the arm cavity mirrors. However, previous increases in optical power have highlighted a major limitation : the presence of one to a few microscopic absorbing defects in the coating of the mirrors. Theses defects mainly of metalic nature causes local absorption inducing optical aberations and excess optical losses. This not only limits the maximum power achievable in the high-finesse cavities but also degrade the control of the instrument. The presentation will describe the development of a new optical measurement bench able to detect these microscopic defects on dielectric mirrors on surfaces up to 620 mm in diameter using wavefront measurements to observe the aberations induced from an absorbing point excited by a 200W laser at 1064nm. This bench will ensure that the most critical mirrors of the gravitationnal wave detectors has no locally absorbing defects, but will also allow to further improve the coating deposition process conditions to prevent the occurrence of this type of defect. The latest results obtained on 350 mm mirrors will be showcased.

Freeform optical components offer expanded design freedom, improved performance, and reduced element count, yet their wider adoption is limited by the shortage of manufacturing methods capable of producing supersmooth freeform surfaces. Current chemical-mechanical polishing methods provide good form accuracy but cannot achieve the angstrom-level smoothness required for pulsed high-power laser and EUV applications. This work aims to develop a sub-aperture CNC-based polishing process capable of producing freeforms with local radii of curvature down to 0.1 m with few-angstrom roughness. Process parameters, tooling, cloths, and slurry formulations are evaluated with emphasis on minimizing surface roughness. Form accuracy and micro-roughness are characterized using interferometry and white-light interferometry, while photothermal deflection identifies subsurface defects. Laser-induced damage threshold testing determines suitability for high-power laser applications.

Freeform optics can enable cutting edge optical systems through increased aberration correction to enable wider fields of view, higher resolution, and lower size, weight, and power (SWaP) designs. However, freeform optics come with challenges in design, manufacturing, and alignment due to their nontraditional shapes. To address challenges in the alignment process of freeform optics, we have created a system that will self-align using a motorized mount and optical feedback fed into an optimization software package. This system is an important first step towards an actively aligning a freeform optical system. Actively aligning systems will enable complex freeform elements to be aligned in a fraction of the time and effort, as well as allow for the realignment of systems remotely or in dynamic environments.

Freeform optics enable complex optical designs unattainable with traditional spherical or aspherical surfaces. They allow enhanced system performance, compactness, and improved aberration correction, which are critical for advanced imaging, sensing, and space applications. However, the manufacturing and testing of freeform optics present significant technical challenges, particularly in achieving nanometric surface accuracies and precise metrology for highly non-axisymmetric shapes. This paper presents the criteria established at Safran Reosc to define and assess complex freeforms, highlights recent achievements on missions such as Microcarb, Sentinel 2 and ELT, and discusses the manufacturing and metrology strategies developed to meet stringent specifications for future generations of freeform optics.

The 20th and early 21st centuries have seen significant growth in the physical size and complexity of astronomical land-based telescopes. These scale increases, combined with tighter image-quality requirements arising from a combination of scientific demands and improvements in technology, have led to the development of active optics for telescope control, where wavefront sensors combine with actuators to drive the shape and position of optics in closed loop, correcting for deflections caused by gravity orientation and temperature changes. Active optics for large telescopes was conceived and developed in the late 1970s, 1980s, and 1990s, and, arguably, only brought to full maturity in the early 2000s. At this point in time, we stand poised on the brink of the Extremely Large Telescope (ELT) era, where apertures in the 10 m range from the 1990s generation of optical–infrared telescopes have leaped by factors of two to four in the upcoming generation of telescopes. At this scale, optical flexures and deflections are amplified compared to the current generation of telescopes, and the combination of open-loop modelling for initial optics positions and shapes, and wavefront sensing for closed-loop control and convergence, is seriously challenged. Since the late 2000s, a new approach, based on the direct metrology of optical components and instrument interfaces, has been developed. Direct metrology offers an interesting intermediate alignment stage between open-loop modelling of positions and closed-loop wavefront sensing. This paper discusses the development and application of these approaches to a range of large telescopes, including optical and radio telescopes.

This presentation will provide a comprehensive overview of European Space Agency (ESA) ongoing efforts to prepare for the next generation of optical Earth Observation missions. First, we will present the science-driven Earth Explorers and Scout missions addressing key scientific issues, followed by an update on preparations for future Meteorology and Copernicus missions. Second, we will present the pre-development activities of innovative instrumental concepts and associated technologies engaged to prepare the future of Earth Observation optical missions. Finally, we will highlight the activities focused on the preparation of compact optical payloads for small satellites.

The Nancy Grace Roman Telescope is a NASA observatory designed to unravel the secrets of dark energy and dark matter, search for and image exoplanets, and explore many topics in infrared optics. Scheduled to launch no earlier than October 2026, this 2.4 meter aperture telescope has a field of view 100 times greater than the Hubble Space Telescope. The mission is currently in its final integration and testing phase, where the telescope and its two instruments were aligned together to ensure proper pupil matching. To verify this alignment, multiple point sources above the entrance pupil of the telescope illuminated the optical path through the telescope-instrument system, and shadows of various obstructions in the system were analyzed using machine learning algorithms to determine the pupil matching error. This presentation reviews the test results and the machine learning algorithms employed, and compares them to our uncertainty predictions based on a modeled Monte-Carlo analysis of the test.

The pre-focal stations of the Extremely Large Telescope contain the final optical components before the collected light is focused into the various scientific instruments. The two elliptical fold mirrors in each station must be of very high quality to maintain the accuracy of the wavefront of the collected light. These mirrors were polished by Glyndŵr Innovations Ltd, and a Ritchey-Common test was utilised for surface error metrology of the 1460 mm wide M6N mirrors. To meet the required flatness specification, the uncertainty of the test had to be exceptionally low, and all sources of error and uncertainty had to be carefully minimised. A test uncertainty of less than 14 nm RMS for the full aperture was achieved to allow the two M6N mirrors to be successfully polished to the specification. The method by which this uncertainty was achieved is detailed through the design and verification of the test.

Assembly of precision optical systems is generally not achievable by precision placement alone; alignment steps are required to correct for manufacturing and tolerance variations. At present this is often manual, requiring well trained staff at significant cost. Although there are numerous examples of academic, and industrially, implemented automated alignment systems there is no generally accepted framework for applying system identification, complexity classification and design rules for automation into optical systems. In this presentation we will present a framework for identifying and classifying an alignment problem according to the complexity from the perspective of system automation. In addition we will explore the process by which the complexity of the problem may be manipulated by design choices, and the implications for cost/benefit analysis and the design process.

This work presents a technique for accurately measuring the shape of deformable, non-specular convex surfaces, such as elastomeric membranes commonly used in soft robotics. The primary goal is to optically characterize these surfaces using a laser triangulation system. An experimental setup was developed in which a membrane was subjected to varying pressures and voltages, and its deformation profile was captured using a CMOS sensor. A laser line was projected onto the surface, and an algorithm reconstructed its three-dimensional geometry by analyzing multiple profiles acquired at 15-degree rotational intervals. The results demonstrate that the proposed method provides a reliable and effective approach for the optical characterization of soft, non-reflective materials.

This work presents the development and implementation of an experimental setup for the optical characterization of concave surfaces using flat, dynamic, polychromatic, off-axis null screens. The system was designed through exact inverse ray tracing to optimize deflectometric performance. Elliptical patterns composed of circular spots arranged in a semi-radial distribution were employed to maximize surface coverage. To enhance sampling density without disturbing system alignment, a complementary pattern with similar geometry was introduced, enabling dynamic measurement capabilities. The technique was applied to three concave mirrors. The results demonstrated a precision of approximately 10 μm rms, with strong consistency across reconstructions obtained at varying sampling densities. Notably, increasing the number of sampling points improved the local resolution of surface defects, confirming the method’s effectiveness for high-fidelity surface evaluation.

Designing opto-mechanics for laser systems using metal Additive Manufacturing (AM) can reduce a system’s volume & weight, consolidate sub-assemblies, integrate multi-functional elements, and can lead towards fully monolithic systems. We introduce specialized techniques to design, manufacture and test compact metal additive manufactured monolithic flexure optical mounts for mm-scale mirrors, windows and lenses. We developed optical testing of µ-radian laser beam pointing errors to quantify optical boresight drift over temperature. We also developed high-resolution imaging polarimeters for milli-radian polarization retardation measurement, to critically evaluate the effects of optics mounting, assembly and bonding, as well as differential thermal expansion of optics in metal mounts. We designed novel metal AM monolithic flexure optical mounts for tip-tilt adjustment, and flexures to retain an optic free of adhesives. These are benchmarked against top-in-class traditionally manufactured mounts, while exposed to thermal load, shock, and vibration conditions applicable to robust laser systems.

LED-based illumination has become increasingly attractive for spectroscopy, imaging, and sensing applications thanks to their spectral diversity and compactness. However, efficiently combining the emission from multiple LEDs into a single, well-defined output remains a major optical design challenge. The overlap of multiple LED sources often leads to significant étendue mismatch, non-uniform illumination, and reduced optical efficiency. We present an overview of recent advances in the optical design of multi-LED systems, from state-of-the-art methodologies to a novel compact illumination architecture employing a single freeform mirror to collect and combine the LED emission beams. Particular attention is given to the role of the freeform mirror to spatially and angularly merge different LED channels, alongside an evaluation of the system’s optical efficiency, compactness, spectral homogeneity, and robustness. This design performance is supported by experimental validation within a proof-of-concept demonstration, paving the way towards its implementation in spectroscopic sensing applications.

The design of optics has seen very significant advances over the last seven decades or so, a lot of which has been due to the tremendous increase in the power of computing & software. In 1675, Isaac Newton said that “If I have seen further, it is by standing on the shoulders of giants”. The same is true of the optical designers of my generation in that we have benefitted so much from the work of the “giants” of previous generations. The presentation will therefore include brief synopses of the contributions of a few of these giants. Some selected examples will be given of the advances over the computer age in the means of designing optics and also the developments in specific optical devices. The presentation will be dedicated to the memory of John Greivenkamp, a great educator in optics, who was to have been its joint author.

Microlenses and microlens arrays are essential in applications like imaging, fiber coupling, and laser beam control. They are defined by parameters such as diameter, radius of curvature, conical constant, and height. A common fabrication method involves creating photoresist pillars via photolithography, melting them into lens shapes (reflow), and transferring them onto a substrate through etching. Variations in photoresist volume and etching uniformity can affect lens quality. This paper introduces a lithography-based strategy using a Direct Writing Laser (DWL) to control photoresist volume through pre-reflow perforations. The method provides a pathway for improving uniformity and yield in large-scale microlens production.

This contribution presents newly developed hybrid polymer materials that show great prospect meeting the requirements for micro- and nanopatterning ability in combination with optical integrity, long-term temperature stability, and system integrability, especially necessary for co-packaged optics (CPO) application technology. Established hybrid polymers such as OrmoComp®, have commercial use mainly in the production of micro-optics for consumer electronics. However, applications as passive optical elements such as waveguides, require low optical loss materials with even higher optical integrity and reliability under sustained thermal stress. New waveguide materials named OrmoCoreLL_XP and OrmoCladLL_XP show significantly reduced, material-intrinsic optical losses as low as 0.05 dB/cm at 1310 nm and 0.09 dB/cm for 1550 nm which is an order of magnitude lower than generic hybrid polymer products, sustaining optical properties even after 1000 h at 130 °C.

Optical metasurfaces—ultrathin arrays of precisely engineered nanostructures—are reshaping biomedical imaging and sensing by enabling unparalleled control over light at the nanoscale. Their ability to manipulate phase, polarization, and near-field interactions within a compact footprint has led to substantial advances in high-resolution imaging, including achromatic focusing, phase-enhanced contrast, and extended depth-of-field techniques. At the same time, emerging high-Q resonant metasurfaces and hybrid plasmonic–dielectric platforms are enabling highly sensitive, label-free biosensing capable of detecting molecular and cellular events in real time. These innovations are accelerating the development of portable, integrated diagnostic systems tailored for point-of-care use. This short review highlights recent progress in metasurface-enabled biomedical technologies and outlines future opportunities for achieving multifunctional, high-performance optical devices that bridge fundamental photonics with clinical needs.

The Instituto de Astrofísica de Canarias has been working on acquiring, installing, and calibrating several optical manufacturing machines, to become a self-sufficient provider under the name of Advanced Optical Systems Center (CSOA). Two laboratories are available for this purpose. One is dedicated to small optics with a diameter under 500 mm, which is equipped with grinding, polishing, ultra-polishing, and coating machines. The other laboratory for large optics, with a diameter of less than to 1500 mm, and it is equipped with polishing and coating machinery. In this communication, we will focus on the small optics manufacturing laboratory, which contains all the necessary instruments for the complete manufacturing of optical elements, from start to finish. This includes all stages, from cutting the optical element block to ultra-polishing using ion beam figuring. We will introduce each machine employed in optical manufacturing and explain its capabilities. Furthermore, we will also discuss the optical materials processed, the characterisation tests performed, and the measurement methods applied. Finally, we will present our current work and our long-term manufacturing goals for optics with diameters down to 500 mm.

This paper describes the design and manufacturing of a lightweighted seven-mirror metallic telescope, which is to be used for aviation-based quantum communication. The unobscured, afocal system features an entrance pupil of 100 mm and is designed for 810 nm and 1550 nm wavelengths. In addition to the two mirror substrates, which are integrated by using a snap-together approach, the lightweighted telescope features a topology-optimised housing and a fully integrated fast steering mirror. The mirror substrate M1/M3 includes two optical surfaces, while the mirror substrate M2/M4/M6 contains tree optical surfaces. The latter substrate was realised in a servo-assisted freeform machining while using ultra-precision manufacturing technology.

The ELT M5 Mirror, measuring 2.7 m × 2.2 m, will be the world's largest tip-tilt mirror and one of the largest Silicon Carbide with Chemical Vapor Deposition (SiC-CVD) brazed mirror —while also meeting high optical quality requirements. M5 presents unique and significant challenges due to its large size, reduced edge margins, complex thickness management, reproducibility of SiC-CVD layer deposition, susceptibility to bending and quilting effects, the presence of brazed joints, and stringent wavefront error (WFE) specifications. These factors combine to make both polishing and metrology highly demanding. To address these challenges, we have implemented an integrated approach combining conventional and innovative tools and processes, aimed at ensuring efficient and safe production within a reduced timeline. A dedicated polishing station has been established, along with a specialized WFE test bench that enables rapid and automatic measurements to nanometer-level precision. Moreover, in-situ metrology tools have been deployed to monitor the mirror at several intermediate stages, further enhancing the efficiency of correction steps. This presentation will detail the methods employed and present the latest performance results achieved on the M5 mirror.

A bioplastic diffraction grating is fabricated from chitosan extracted from crab shells sourced from the seafood industry. The grating is deformable and employed in experiments as a concave diffractive element. We report variable diffraction angles and first-order efficiency as functions of grating curvature. Results are presented for gratings prepared from various chitosan mixtures.

The NASA Extreme Ultraviolet Explorer (EUVE) launched in 1992 was the first and last dedicated space telescope to operate in the EUV band. Although difficult to access due to the large interstellar extinction, the EUV range is important to understand the physical processes happening in million degree plasmas such as in hot white dwarf atmospheres, accretion processes, the interstellar medium and others. In addition, EUV radiation drives the atmospheric escape of all planets and is therefore critical to measure in order to understand the impact of host stars on the habitability potential of their exoplanets. Since the 1990s, technological advances have been made and are now enabling a renaissance for EUV missions, thanks in part to the possibilities offered by nanofabrication techniques to create high-efficiency diffraction gratings tailored to that wavelength range. We will summarize the recent advances made in the fabrication of ultra-low blaze angle diffraction gratings in the context of the NASA CubeSat MANTIS (Monitoring Activity of Nearby stars with ultraviolet Imaging and Spectroscopy), and will present preliminary test results on realized prototypes.

3D printing of optical functions enables lenses and components that merge multiple functions, simplifying and compacting optical systems. Recent advances stem from additive processes using nano‑doped polymers or glass, while femtosecond‑laser structuring modifies material refractive index to create phase gradients. Unlike traditional ablation‑based methods, these techniques are more environmentally friendly. This presentation uses laser‑writing to fabricate annular phase masks (materials: Corning 9754, EagleXG, fused silica) with ±π phase shifts, compared experimentally to photolithographic masks. A camera with the mask at its pupil records scenes at varying depths; images are deconvolved with a 9 × 9 Wiener filter and evaluated by the Learned Perceptual Image Patch Similarity (LPIPS) criterion. Femtosecond direct writing allows transparent materials from visible to IR and integrates complex functions into optics unsuitable for diamond turning or molding.

To address SWaP-C challenges, ONERA is developing Gradient Index (GRIN) optics using chalcogenide glasses transparent in the infrared range, with the goal of reducing the size and cost of optronic systems. A Na⁺/Ag⁺ ion-exchange process has been developed but required improvements to limit cracking and glass degradation. Current research focuses on the synthesis of radial GRINs and optimization of the process, notably through the addition of silica to the nitrates and the use of a PTFE support, which enhance silver diffusion and lens quality (Δn ≈ 0.1). The process now enables the fabrication of divergent GRIN lenses, while ongoing studies aim to design convergent lenses using new AgI- or CuI-doped glasses. The ultimate objective is to manufacture spherical GRINs by molding axial GRIN preforms with optimized optical performance.

The Canary Islands Institute of Astrophysics (IAC) has been improving its capabilities for the design and manufacture of optical components for several years, especially the development of protective silver coatings for telescope mirrors up to 1.6 meters in diameter. These mirrors are of great interest to the astronomical community due to their high reflectivity, but in harsh, sulfur-rich environments such as observatories, silver degrades very rapidly and Our current research focuses on improving the long-term stability and environmental resistance of silver coatings by optimizing deposition parameters and applying protective layers.

In this study, laser light scattering was used to detect small particles within an optical coating chamber. An optical setup for in-situ monitoring of the particles was realized utilizing a laser sheet obtained with 458 nm, 400 mW diode laser and camera-based imaging. Various optical setups were tested to optimize the sensitivity. A modular, adaptable system was developed and validated in industrial coating systems.

In this paper, we present, full-field, and real-time precision scanning method of planes functional surfaces of components, for detection and measurement of flatness defects by optical way. This method consists of scanning the functional surface, with laser beam, witch vehicle a microscopic structure, then generating an interference pattern that highlights the shape defects present on all inspected surface. This optical system has a variable detection sensitivity that can be adapted according to the precision of component surface being inspected. This method, is used for precision measurement deformation in shape or absolute forms in comparison with a reference component form, of optical or mechanical components, where dimensions of inspected surfaces can range from two mm² to larger areas. The optical device used allows a significant dimensional surface magnification of up to 1000 times the area inspected for micro-surfaces, which allows easy processing and reaches an exceptional nanometric imprecision of measurements.