The Wide-field Spectroscopic Telescope (WST) is a proposed 12-meter segmented facility optimized for seeing limited observations in the visible and designed to operate both a high-multiplex multi-object spectrograph and a panoramic integral field spectrograph (IFS). The WST IFS concept builds on instruments such as MUSE at the VLT (Very Large Telescope), using field splitters and image slicers to reformat a large field into pseudo-slits feeding spectrographs with two optimized spectral channels. This paper presents the spectrograph architecture developed for the WST IFS, aiming to achieve high through put and image quality over a wide wavelength range in a cost-effective manner. We investigate the use of curved detectors as a means to simplify the spectrograph layout, reduce aberrations, and potentially improve efficiency. This study establishes a promising baseline for the IFS spectrographs and assesses the benefits of incorporating curved sensors that can guide the development of future large-scale integral field spectrographs.

Significance:Extended depth-of-focus (EDOF) intraocular lenses (IOLs) aim to provide improved visual performance over a range of distances, but their clinical outcomes are still sensitive to individual biometric variability. Improving the robustness of EDOF IOL optical performance to these patient-specific variations is critical to enhance visual predictability and patient satisfaction following cataract surgery. Aim:We aim to determine if freeform surfaces can improve the robustness of EDOF IOLs by maintaining consistent optical performance (refractive error, depth of field) despite individual biometric variations. Approach:A database of synthetic eyes was adapted to simulate pseudophakic eyes. The post-operative performances (refractive error and depth of field) for three types of EDOF IOLs (L1, L2, L3) were estimated using polychromatic Visual Strehl ratio based on the Optical Transfer Function, with photopic wavelength spectrum for a 3 mm and a 5 mm entrance pupil diameter. L1 is a standard refractive EDOF; L2 is identical to L1 but with a freeform back surface optimized in-eye; L3 is similar to L2 but calculated by a model trained to predict freeform surfaces, using preoperative biometric data (higher-order aberrations of the cornea; effective lens position, calculated from preoperative data; ELP-retina distance; and transverse position of the lens). Results:The addition of a freeform surface allowed us to significantly reduce the difference between the target refraction and subjective refraction, in polychromatic condition, for small and large pupil sizes while maintaining the depth of field. Performances with L3 were equal to L2. Conclusions:The use of a freeform surface can significantly reduce the impact of individual biometric variations such as corneal aberrations and transverse IOL positioning on EDOF behavior lenses, for small and large pupil sizes.

Many different scientific applications require sub-micro arcsecond precision astrometry, including researching rocky exoplanets in the vicinity of the Sun and studying dark matter. The Habitable Worlds Observatory (HWO) is a promising candidate to carry an astrometric instrument because it provides a stable, space-based telescope with a large aperture, which allows faint sources and small displacements to be observed. This paper presents the characterization of an appropriate detector for an astrometric instrument: the 46Mpx Gigapyx from Pyxalis. Moreover it explains the implementation of a testbed enabling interferometric characterization of pixel positions. Finally, the paper introduces a method for calibrating the telescope's optical distortion. This method was implemented in simulation and tested thanks to an optical bench developed at IPAG in France.

High precision differential astrometry assesses the positions, distances, and motions of celestial objects in relation to the stars. The focal plane of such space telescope must be calibrated with a precision down to the level of 1e-5 pixel in order to be able to detect Earth-like planets in the close vicinity of the Sun. The presented characterization bench is designed to improve the technology readiness level for the following key points: calibration of new detectors with a high number of pixels and correcting the field distortion using stars in the field of view. The first aim of the project concentrates on the characterization of a 46 megapixels sensor from PYXALIS, to assess its typical parameters using an integrating sphere. The next objective intends to map the intra and extra pixel quantum yield of the detector with a precision of 1e-5 pixels and investigate the evolution of the pixel geometry in response to environment fluctuations. To conduct these tests, an optical bench is designed with an LCD screen and a doublet, used as a source that allows directing light to specific groups of pixels. Interferometric calibration of the detector pixel centroid position will be achieved using fibers that illuminate the detector with Young's fringes. To characterize the distortion of the detector, a diaphragm will produce adjustable optical aberrations to be corrected and therefore change the source sensor positional relationship. The final step involves the simulation of a star's field, which will be imaged on the detector to assess optical quality.

Purpose: Fuchs endothelial corneal dystrophy (FEDC) is by far the most common corneal endothelial diseases in Western countries, and 50% of keratoplasties are carried out to treat endothelial diseases. New treatments are also emerging (Descemetorhexis only, rock‐inhibitors, mTor‐inhibitors, FGF‐1). It will therefore soon be vital to be able to determine the stage of each patient in a simple and reliable way, in order to personalize treatment. Visual acuity, retroillumination, specular microscopy and thickness mapping are the 4 pillars of the examination. However, current retro‐illumination images are of insufficient quality. Aim: to present the first series of FECD observed using new‐generation retroillumination. Methods: We developed a prototype retroilluminator by modifying a slit lamp with the aim of obtaining high‐resolution images, without parasitic reflection and without dazzling the patient. We then prospectively photographed 200 FECD patients. The images were then classified by 3 independent observers according to the modified Krachmer classification, which is the most widely used in the literature: it distinguishes patients according to the number of Guttae, the size of the area of confluent Guttae and the presence of oedema. Results: The prototype produced clear, glare‐free images in over 95% of cases. Persistent reflections were observed exclusively in pseudophakic patients. The high resolution made it possible to observe all the Guttae and to challenge Krachmer's grade 2 classification (more than 12 non‐confluent drops), which included a major diversity of patients, some of whom had thousands of non‐confluent Guttae. We also highlighted for the first time to our knowledge 2 new elements: the high frequency of radial alignment of Guttae, often over 360°, and the presence of Guttae in the periphery of the endothelium, suggesting that a cell migration anomaly is involved. Conclusions: Innovative retroillumination images challenge Krachmer's classification by providing exceptional precision. They will make it easier to distinguish between sub‐groups of patients with different visual repercussions and evolutionary profiles. Easy to use, this new device should help to improve both our understanding of FECD and its routine management.

This study presents a comprehensive system analysis for an instrument onboard the Habitable Worlds Observatory (HWO), designed for high-precision, high-accuracy differential astrometry, with the primary scientific goal to determine the mass of Earth-like planets around the nearest Sun-like stars. The analysis integrates the definition of the mission profile, the instrumental concept architecture, and an error budget that breaks down the key contributors to the sub-micro arcses precision required for a single measurement. A portion of this budget addresses photo-center estimation for both the target and calibration stars used in differential astrometry. Other major contributors are related to instrumental control of systematics in the reconstruction of differential angle measurements from pixel data (focal plane calibration) to on sky line of sight (telescope distortion calibration). End-of-mission astrometry requires multiple observations (typically 100) of the same target distributed over the mission lifetime. We assess the mission profile to estimate the fraction of survey time required for astrometric survey to achieve the science objective. The proposed architecture of the instrument concept is derived from error budget and mission constraints based on a large visible detector array composed of an assembly of multiple CMOS sensor chips resulting in an overall gigapixel focal plane. We evaluate the Technology Readiness Level (TRL) and propose a way forward reaching TRL 5 level for key technologies by the Mission Consolidation Review in 2029.

While retro-illumination of the anterior segment is part of the routine examination in ophthalmology, capturing a quality image is very difficult. We have therefore developed a new imaging device by modifying a slit lamp. By using a far-red light source, a monochrome sensor and modifications to the optical path, we were able to obtain high-resolution images, without reflection and without dazzling the patient. Here, for the first time, we present a number of potential applications for this revisited imaging technique.

Astrometry is one of the oldest branches of astronomy which measures the position, the proper motion and parallax of celestial objects. Following the Hipparcos and Gaia missions that have measured several billions of them using global astrometry, we propose to increase astrometry precision on pointed objects using differential astrometry in a large field in order to unravel rocky planets in habitable zones of stars in the Sun vicinity and investigate the nature of dark matter in galactic environments as recommended by the ESA Senior Committee in the Voyager 2050 prospective. Substantial technology developments in a number of critical areas is needed in order to reach the highest required precision of sub-micro-arcsecond. One of them is CMOS image sensors using the stitching technique to merge the multiple design structures on the wafer and produce array with very large number of pixels. Another one is to calibrate the pixel positions using projecting modulating interferometric laser fringes on the array. Finally, the distortion of the optical system can be monitored and compensated using reference stars as metrology sources. The final precision depends on the diameter and the field of view of the telescope that is used as well as the time spent on each target. We present here the science goals that can be achieved with such missions either within the framework of an ESA Medium-class mission or even in the NASA most challenging Habitable Worlds Observatory, a large space telescope recommended by the American Astronomy and Astrophysics prospective for the 2020s and designed specifically to search for signs of life on planets orbiting other stars.

High precision differential Astrometry is the branch of astronomy that evaluates the relative position, distance and motion of celestial objects with respect to the stars present in the field of view. A mission called Theia has been submitted in 2022 for ESA's M7 call for missions, using a diffraction-limited telescope about 1m in diameter and with a field of view of 0.5 degrees, capable of achieving sub-micro-arcsecond angular accuracy, corresponding to 1e-5 pixel on the detector. Such precision makes it possible to study the nature of dark matter in our galaxy and to reveal the architecture of exoplanetary systems close to the Sun, down to the mass of the Earth. The aim of the experimental tests presented in this poster is to improve the TRL of 2 specific aspects: the calibration of new CMOS detectors with very large number of pixels and the calibration of the telescope aberrations.First, a key element of such a space telescope is the focal plane, which must be calibrated spatially with an extreme precision down to the 1e-5 pixel level. Previous work has shown that this is possible with small detector matrices (80x80 px) [1]. The goal is now to check the performances and validate this method with the new very large detectors. Pyxalis, a company based near Grenoble, is developing very large detectors (8000x5000 px) that have a low noise level and high sensitivity. The aim is to characterize and validate this type of detectors in a laboratory demonstration (see poster Pancher et al.), to ensure that the performance achieved meets the required specifications. We present the results of these characterization in this contribution.The telescope stability is also a sensitive issue. Recent work [2] has shown that the reference stars in the field of the telescope can be used as actual metrology sources in order to compute the field distortion function. Our simulations allow to model the optical aberrations with bivariate polynoms. The effects on the calibration accuracy of the degrees of the polynoms, the number of reference stars and the tilt perturbation of the M2 mirror are investigated. This poster will present the latest results obtained on a test bed developed to experimentally study the performances of this new field calibration method.

The Evanescent Wave Coronagraph (EvWaCo) is a type of Lyot coronagraph that uses an achromatic focal plane mask comprising a lens and a prism in contact. The National Astronomical Research Institute of Thailand (NARIT) plans to install an EvWaCo prototype equipped with an adaptive optics system (AO) to correct the aberrated wavefront in real-time at the unused left Nasmyth port of the Thai National telescope. To prepare for this installation, a large adapter with a diameter of 1.3 m and twelve carbon fiber poles serve as the supporting beams to hold the prototype. This work focuses on the mechanical design and testing of the large adapter, considering the prototype requirements and installation limitations. In particular, mechanical deformations and stress distributions are analyzed under survival conditions. The maximum weight of the prototype is 200 kg, and a folding mirror installed in a translation stage is placed inside the large adapter. The structural optimization uses the finite element method to deal with the constraints and ensures a high performance. The carbon fiber poles comprise carbon fiber-reinforced polymer (CFRP) that reduce the weight by approximately 30% compared to an all-aluminum structure. Each carbon fiber pole weighs about 1.75 kg, and our testing results show that it can support up to eight times the prototype's weight. The epoxy adhesive, used to join different materials, can withstand a pull-out strength of up to three times the prototype's weight. The installation of this adapter is expected to start by the end of 2024.

With sub-microarcsecond angular accuracy, the Theia telescope will be capable of revealing the architectures of nearby exoplanetary systems down to the mass of Earth. This research addresses the challenges inherent in space astrometry missions, focusing on focal plane calibration and telescope optical distortion. We propose to assess the future feasibility of large-format detectors (50 to 200 megapixels) in a controlled laboratory environment. The aim is to improve the architecture of the focal plane while ensuring that specifications are met. The use of field stars as metrological sources for calibrating the optical distortion of the field may help to constrain telescope stability. The paper concludes with an attempt to confirm in the laboratory the performance predicted by simulations. We will also address the possibility of using such techniques with a dedicated instrument for the Habitable World Observatory.

Optimizing freeform systems can encounter convergence difficulties due to the many degrees of freedom that these surfaces bring to optical systems. Moreover, the description of these freeform surfaces in a polynomial basis may impose prior knowledge on the shape of the surface. In this presentation, we will showcase a differential ray tracer with NURBS capabilities called FORMIDABLE. In contrast to available commercial optical design software, such as Zemax OpticStudio and Synopsys Code V, this library ican simulate and especially optimize Non-Uniform Rational B-Spline (NURBS) surfaces. The key advantage of NURBS lies in their ability to locally describe an optical surface, thereby minimizing preconceived notions about the surface shape, aside from the surface sampling determined by the density of the NURBS representation. The main drawback, however, is the significant increase in the degrees of freedom within the optical system, making the optimization of these surfaces a complex task with a conventional commercial optical design software. FORMIDABLE's implementation of differential ray-tracing capabilities allows faster convergence of systems described by many degrees of freedom and makes optimization with NURBS surfaces viable. The features of FORMIDABLE will first be described. Then its capabilities will be illustrated with the optimization of a classical non-reimaging Three-Mirror Anastigmat (TMA) by considering either a description of surfaces by NURBS or a description by the polynomial basis XY. Then, this optimized TMA will be compared with its equivalent optimized with Zemax OpticStudio. To enable this software comparison, we will use the same starting point and practically the same merit function. Standard metrics, such as Root Mean Square (RMS) spot size across the field of view (FOV) will be used to assess the imaging quality.

Situational awareness requires systems with a wide field of view and a high angular resolution. Tackling both requirements is easier using freeform optics and a curved sensor and allows for compact systems. In this paper, we present an imaging system that fulfills these requirements in the visible spectrum, and the steps in the optimization process that lead to a viable system in terms of stray light.

The National Astronomical Research Institute of Thailand, together with the Institut d'Optique Graduate School and Centre de Researche Astrophysique de Lyon, has been developing the Evanescent Wave Coronagraph (EvWaCo) a new kind of Lyot coronagraph that uses a lens and prism placed in contact as its focal plane mask. By the principle of frustrated total internal reflection, EvWaCo enables an achromatic rejection and ability to collect the light from the star and the companion. An EvWaCo prototype equipped with adaptive optics will be installed at the Thai National Telescope as an on-sky demonstrator. This demonstrator will work on a 1.2 x 0.8 m(2) elliptical sub-aperture of the Thai National Telescope to reach a raw contrast of 10(-4) at 3 lambda/D over the wavelength range [600 nm, 900 nm]. The completed optical design contains all the essential light path channels in high contrast imaging fitted inside a 960 mmx960 mm optical breadboard, namely the guiding camera channel, companion channel, star channel, and wavefront sensing channel. We also show the results of the tolerancing and straylight analysis.

Novel freeform optical design methods can be classified in two categories, depending on whether they focus on the generation of a starting point or the development of new optimization tools. In this paper, we design a freeform three-mirror anastigmat (TMA) and compare different surface representations using either a differential ray tracer as a new optimization tool or a commercial ray tracer (ANSYS-ZEMAX OpticStudio). For differential ray tracing, we used FORMIDABLE (Freeform Optics Raytracer with Manufacturable Imaging Design cApaBiLitiEs), an optical design library with differential ray tracing and Non-Uniform Rational B-Splines (NURBS) optimization capabilities, available under the European Software Community License (ESCL). NURBS allow a freeform surface to be represented without needing any prior knowledge of the surface, such as the polynomial degree in polynomial descriptions. OpticStudio and other commercial optical design software are designed to optimize polynomial surfaces but are not well-suited to optimize NURBS surfaces, requiring a custom optical design library. In order to demonstrate the interest in using NURBS representation, we designed and independently optimized two freeform telescopes over different iteration cycles; with NURBS using FORMIDABLE or with XY polynomials using OpticStudio. We then compared the resulting systems using their root mean square field maps to assess the optimization quality of each surface representation. We also provided a full-system comparison, including mirror freeform departures. This study shows that NURBS can be a relevant alternative to XY polynomials for the freeform optimization of reflective three-mirror telescopes as it achieves more a uniform imaging quality in the field of view.

Novel freeform optical design methods can be classified in two categories, relevant to the generation of a starting point or to the development of new optimization tools. In this paper, we design a freeform TMA optimized with different surface representations using either a differential ray-tracer as a new optimization tool, or commercial ray tracer (ANSYS-ZEMAX OpticStudio) for comparison. For differential ray tracing, we use FORMIDABLE (Freeform Optics Raytracer with Manufacturable Imaging Design cApaBiLitiEs): an optical design library with differential ray tracing and NURBS optimization capabilities under European Software Community License (ESCL). NURBS allow to represent a freeform surface without needing any prior knowledge on the surface, such as the polynomial degree in polynomial descriptions. However, commercial optical design software are designed to optimize polynomial surfaces, but are not well-suited to optimize NURBS surfaces. This requires to use a custom optical design library. To demonstrate the interest of using NURBS representation, freeform telescopes are independently optimized with NURBS using FORMIDABLE, or XY polynomials with OpticStudio over different iteration cycles. We then compare the resulting systems using their RMS Field Maps to assess the optimization quality of each surface representation. We also provide a full-system comparison, including mirror freeform departures. This study shows that NURBS can be a relevant alternative to XY polynomials for freeform optimization of reflective 3-mirror telescopes.