In 2017, the European Southern Observatory (ESO) awarded a contract for the Polishing, integration and final figuring of the Segment Assemblies of the primary mirror (M1) for the Extremely Large Telescope (ELT) to Safran Reosc. Since then, the design and commissioning of a production unit dedicated to ELT M1 has been accomplished and the plant has been producing many mirrors since spring 2022. We will introduce the smart factory, its processes and their automation that enabled reaching the current throughput of one mirror per day. We will then present the status of the project, some lessons learned and highlight the successes that have been achieved so far.

The next generation of reflection gratings for future high-energy space observatories needs a high degree of customization. Making such gratings will require the use of increasingly complex nanofabrication techniques. One of the current challenges we are investigating is the precise patterning of grooves onto curved substrates, which is needed for effective aberration-correction. We report on our use of electron-beam lithography to pattern large-format gratings on cylindrical substrates. We will discuss the fabrication steps involved, from the alignment of the substrate to the actual writing strategy, and we will summarize our characterization efforts based on interferometric measurements. Future steps will be discussed, including the patterning of a segmented X-ray mirror.

Over the past decade, Optimax has been developing a robotic platform for polishing and smoothing of optics. The robotic platform allows for flexibility and rapid adaptation to different geometries, and significant effort has been applied to improving process and determinism. The robotic platform will enable scaling production of large (up to 500 mm) freeform and aspheric optics much more easily than with commercial manufacturing machines, with improved flexibility to adapt to changing work requirements. This paper with review the robotic platform developments and step through the process of deterministic form correction and predictive smoothing on a simplified geometry.

The IBS2000-project aims to develop a coating machine to coat optics with up to 2m in diameter. IBS is chosen as coating process due to the high optical quality and precision, low losses, and high mechanical and environmental stability. Common limitations regarding the size of the coated optics are overcome due to a novel approach, where both, the substrate and the target material source are movable. The sputter assembly located below the substrate will move linearly, while the substrate rotates on a stationary axis around its center. Simulations are done to validate the mechanical concept with a virtual coater concept. First, the material distribution in the substrate plane is calculated and afterwards combined with the movement of the target carrier and the substrate rotation, which gives a first indication of the 2D distribution. The results will be applied to homogenize the projected coating distribution on the final 2m optics.

Optical patterns, especially surface relief gratings (SRG), are becoming ever-important, with applications ranging from laser mirrors to mixed and augmented reality (MR/AR) devices. In particular, slanted surface relief gratings are essential as in- and out-couplers of light into the waveguide to produce lightweight near-eye AR displays. They allow to suppress higher diffraction orders, maximize light yield, and achieve a wide field of view. The pattern can either be etched directly into the waveguide by reactive ion beam etching (RIBE) or be produced through nano-imprint lithography (NIL). NIL requires the production of a master stamp with defined grating properties. Reactive ion beam trimming (RIBT) is a suitable technology for producing master stamps as it allows manufacturing gratings with varying trench depths and slant angles over a substrate. In addition, it is shown how the shape of the slanted grating can be improved by applying different process parameters.

Optics integrators and users are increasingly demanding that parts be tested after coating. For dichroic and filter manufacturers, this can be difficult for two main reasons. Firstly, the spectral properties of these parts once treated may not be compatible with the 632.8 nm HeNe wavelength, on which common metrology tools such as Fizeau interferometers are based. Secondly, the shape of these samples, with their flat, parallel surfaces, makes them prone to generating back reflections that are difficult to eliminate and affect the accuracy of surface shape reconstruction. Imagine Optic has developed and patented a new approach called POP that brings easy access to the optical testing of such samples, based on the combination of incoherent light at any wavelength and Shack Hartmann wavefront sensing. We will present the technique principle and how it works as implemented in a metrology system we called MESO. We will report the validation process of the approach and showcase results on real samples highlighting the advantages of the technique.

We introduce a Convolutional Neural Network (CNN) designed for precise wavefront retrieval from point-spread function (PSF) intensity images. Our ResNet18-based CNN infers the first 15 Zernike standard coefficients using three PSF measurements symmetrically positioned around the focal point. The CNN is trained on a dataset of 300,000 simulated PSF image sets containing 4th and 6th order aberrations, with wavefront amplitudes of up to 10 λ. We achieve an accuracy exceeding 99% for each individual Zernike coefficient, with uncertainties ≤ λ/30, as validated on a dataset of simulated PSF images. We evaluate the CNN's performance on experimental PSF measurements, and the predictions are compared to direct wavefront measurements from a Shack-Hartmann sensor. The results indicate prediction accuracy better than λ/15 for each of the 15 coefficients. This confirms the CNN's potential for characterizing optical systems with complex aberration distributions of low to moderate amplitudes.

Accurate laser damage testing for Laser MégaJoule (LMJ) fused silica optics is crucial for predicting their lifetimes. However, beam propagation in optics is usually neglected and yet, damage sites are mostly initiated on the exit face of optics. The MELBA testbed in CEA CESTA (France) delivers nanosecond UV laser pulses representative of LMJ optics conditions on a centimeter scale. Our particular imaging system measures the beam spatial profile before and after propagation in samples, enabling quantification of self-focusing induced by the Kerr effect. This metrology is necessary for laser damage parametric studies, particularly when these laser parameters influence the Kerr effect. We present here a study of the impact of a linear-to-circular polarization conversion on laser damage, which highlights the importance of accurately assessing non-linear beam propagation for laser damage tests.

We investigate the feasibility of a full-silica transmission grating acting as a quarter-wave plate at the wavelength of 351 nm as an alternative to an anisotropic crystal. We report on the design, manufacturing process and optical characterization carried out. We evidence the possibility to obtain a full-silica component exhibiting at 351 nm a high damage threshold and a phase retardance of /4 associated with a diffraction efficiency above 98%.

Energy transfer examination of Er3+/Nd3+ to produce a high-performance light conversion layer for enhancing the solar cells' efficiency Abstract Aiming to enhancing the solar cells efficiency, a spectral upconversion layer of a developed oxy-fluorophosphate glass containing Er3+/Nd3+ ions will be produced. The structural changes resulting from the penetration of Nd3+ ions into the glass network will be examined using X-ray diffraction, density and density-based parameters, Fourier transforms infrared, spectra, and Raman spectra. Being a major nerve in the spectral conversion layers, the thermal stability of the produced glasses will be investigated by studying the temperature of glass transition and crystallization using differential scanning calorimetry. Under the influence of appropriate wavelengths, the studied glasses will be pumped, and the resulting light emission will be examined to explore its efficiency as conversion layers for solar cells. Keywords: Solar cell, light upconversion, Er3+/Nd3+, oxy-fluorophosphate glass.

The poster introduces the MELBA setup located at CEA CESTA (France). The MELBA laser delivers a nanosecond UV centimeter-sized laser beam and is dedicated to the study of laser-induced damage and damage growth within the Laser MégaJoule framework. Laser pulses are spatially, temporally and spectrally both shaped and characterized. A dedicated imaging system can measure the non-linear propagation in samples and its consequence on surface damage and filamentation. Recently, it was made possible to adjust the beam polarization from linear to circular.