We report observations of stripe-like features in Enceladus’ plumes captured simultaneously by Cassini's VIMS-IR and ISS NAC instruments during flyby E17, with similar patterns seen in VIMS-IR data from flyby E13 and E19. These parallel stripes, inclined at approximately 16°to the ecliptic and 43°to Saturn's ring plane, appear continuous across images when projected in the J2000 frame. A bright stripe, most visible at wavelengths around 5μm, acts as the zeroth-order diffraction peak of a reflection grating with an estimated groove spacing of 0.12–2.60 mm, while adjacent stripes are attributed to higher-order diffraction peaks. We suggest that this light-dispersing phenomenon originates from an inclined periodic structure within Saturn's E ring. This structure, constrained between Saturn's G ring and Rhea's orbit, likely consists of fresh ice particles supplied by Enceladus’ plumes.

One of the most ambitious goals of modern astronomy is to uncover signs of extraterrestrial biological activity, primarily achieved through spectroscopic analysis of light emitted by exoplanets to identify specific atmospheric molecules. Most exoplanets are indirectly identified through techniques like transit or Doppler shift of the host star’s flux. Long-term surveys have yielded statistical insights into the occurrence rates of different planet types based on factors such as radius/mass, orbital period, and the spectral type of the host star. Initial estimates of terrestrial planets within the habitable zone have also emerged. However, the difficulty of detecting light from these exoplanets leaves much unknown about their nature, formation, and evolution. As the number of rocky exoplanets around nearby stars rises, questions about their atmospheric composition, evolutionary trajectory, and habitability increase. Direct measurement of an exoplanet’s atmospheric composition through its spectral signature in the infrared can provide answers. Measuring the infrared spectrum of these planets poses significant challenges due to the star/planet contrast and very small angular separation from their host stars. Previous research showed that space-based telescopes are mandatory, and unless large primary mirrors (>30m in diameter) can be sent into space, interferometric techniques become essential. Combining light from distant telescopes with interferometric techniques allows access to information at minimal angular separation, operating within the diffraction limit of individual telescopes. Successful demonstrations of on-ground nulling interferometry open a new era for such space-based missions. They are vital to sidestep and tackle these scientific questions. We recently initiated a new study with the European Space Agency to explore the design parameters and the performances related to an interferometric concept based on a single spacecraft and sparse multiple sub-apertures. Launch constraints are linked to the use of an Ariane 6 launch vehicle. Our parametric study covers a range of 1-4 m for the diameter of the telescope and a 10-60 m baseline. The most promising concept working in the infrared range (3-20µm) will be highlighted. This study is conducted by TUDelft in cooperation with KULeuven, CSL/ULi`ege, and Amos with the support of the European Space Agency.

In recent years, advancements in semiconductor technologies have significantly transformed Radio Frequency Power Amplifiers (RFPAs), enhancing their efficiency, size, and performance. Despite these advancements, the design of RFPAs remains intrinsically linked to the specific applications for which they are intended. What proves effective in one context, such as communication technologies, may not be equally suitable in others, such as scientific instruments. This discrepancy highlights the lack of a systematic approach to RFPA design that can be applied across different applications. This paper delves into the fundamental concepts of RFPA design, adopting a comprehensive perspective. It further introduces an alternative categorization of RFPAs, thereby providing a generalized design approach.

Context. The extreme ultraviolet High-Resolution Imager (HRI_EUV) of the Extreme Ultraviolet Imager (EUI) telescope on board Solar Orbiter observes the solar corona in an ∼5 Å wide passband near 174 Å with unprecedented high spatial resolution. Aims. We aim to perform radiometric cross-calibration of the HRI_EUV and the Atmospheric Imaging Assembly (AIA) telescope in order to allow further mutual analyses of the observational data. Methods. We applied a differential emission measure analysis using quasi-simultaneous images taken in seven spectral channels -HRI_EUV and six channels of AIA -and compared the real and the simulated images. Results. The comparison suggests that the real HRI_EUV images have ~40% larger signal than the simulated images predicted by the differential emission measure analysis. Conclusions. With our method we cannot conclude which instrument has errors in the absolute calibration, as it can be the case for either of them or both of them simultaneously, but to a lesser degree. However, in order to improve the accuracy of simultaneous data analysis, one needs to take this discrepancy into account. We see that introduction of the HRI_EUV signal into the DEM analysis modifies the warm plasma with 1 MK. The ability of the method to reproduce HRI_EUV images using only the AIA data further validates the underlying assumptions and our approach. Lastly, we believe the approach can be used as a strategy to establish a golden reference of contemporary EUV imagers.

Purpose: To assesses the link between the in vitro optical properties of the PODFGF multifocal intraocular lens (IOL) and its visual acuity (VA) clinical performance. Setting: The study was conducted at TUDelft (NL), ULiege (BE), the Rothschild Institute (FR), and Beaver-Visitec International (BE). Design: The study analyzed 3 powers of the PODFGF IOL. The in vitro imaging quality was assessed using modulation transfer function (MTF) frequency sweep and through-focus MTF. Multiple figures of merit (FOMs), including MTF at 25-50-100 LP/mm, MTFa, and Strehl ratio, were extracted. Data acquisitions followed 2 ISO norms in green and white light conditions. The correlation with patients’ clinical VA was evaluated. Methods: The methodology had 2 parts: first, characterizing the in vitro properties of the IOL using FOMs, such as MTF, MTFa, and Strehl ratio, with multiple power samples (6 to 35 diopters). The second part analyzed the VA of 413 eyes implanted with FINEVISION-HP (PODFGF). Over 2 years, subjective refraction, uncorrected distance VA, corrected distance VA, uncorrected intermediate VA, distance-corrected intermediate VA, uncorrected near VA, distance-corrected near VA, defocus curve, photopic and mesopic contrast sensitivity, and rotational stability were analyzed. Results: The correlation between in vitro MTFa evaluated from the experimental data on IOLs and the clinical VA performed on implanted patients leads to an accurate prediction of vision capabilities after surgery. Conclusions: This study clinically demonstrates on a large patient cohort that MTFa complements single-frequency MTFs and establishes a mathematical link between MTF at 50 LP/mm, MTFa, and VA. In addition, it connects the 2 ISO model-eye standards and highlights the link between green and white light measurements in accurately predicting VA.

Third-generation gravitational wave detectors will use large mirrors isolated from seismic motion at low frequency, and also cooled down to cryogenic temperatures. To fulfil these two specifications, the E-TEST project explores the possibility of using a purely non-contact radiative cooling strategy. Based on cooling predictions, the paper includes a detailed design of the cryostat and the assembly procedure. A test campaign demonstrated that the proposed strategy succeeded in bringing the temperature of a [Figure presented] dummy mirror down to [Figure presented] in 19 days. These encouraging results are paving the way toward a fully radiative approach for cooling the mirrors of the future Einstein Telescope.

Metamaterials and metasurfaces hold significant promise for space applications due to their compactness and lightweight characteristics. These devices use nanostructures embedded in their flat surfaces to manipulate the electromagnetic field for various purposes. Among their potential applications, metalenses stand out for their prospective role in the next generation of optical instruments deployed in space. Specifically, they offer considerable advantages for free space optical and quantum communications terminals. In intersatellite free space optical communication links, transmitter pointing errors degrade the performance of the link. Nevertheless, optimizing the shape of the transmitted beam through a metalens can improve the communication link performance. In this study, we delve into the application of metalenses for shaping laser beams in intersatellite optical communication scenarios. We present the preliminary design of the metalens and analyze its performance through numerical simulations, analyzing its feasibility and potential in space-based optical communications.

Intersatellite free-space optical communications are the backbone of the future highspeed global communication networks. In orbit, thermo-mechanical loads create perturbations that detriment the performance of these links. Among these perturbations, the transmitter pointing jitter and optical aberrations are of special relevance. We present an analysis of the coupled effects of transmitter pointing jitter and optical aberrations on intersatellite free space optical communications. A mathematical model is presented to evaluate the performance of average bit error probability, probability of outage, and reliability on intersatellite free space optical communication links subjected to these perturbations. Furthermore, the optimum non-aberrated truncated Gaussian beams are obtained for each of these performance parameters for different telescope architectures. The results demonstrate that the performance parameters are highly sensitive to the optimal far-field irradiances. These optimum operation points are then perturbed by Seidel aberrations to study the effect of these aberrations in the system. The results show that optical communication terminals are most sensitive to coma aberrations, mainly due to the induced apparent angle of arrival on the beacon beam. Finally, Monte Carlo simulations of combinations of Seidel aberrations show a strong dependency on the telescope architecture of the sensitivity of the communication performance parameter to the magnitude of the optical aberrations.

The Large Interferometer For Exoplanets (LIFE) is a proposed space mission that enables the spectral characterization of the thermal emission of exoplanets in the solar neighborhood. The mission is designed to search for global atmospheric biosignatures on dozens of temperate terrestrial exoplanets and it will naturally investigate the diversity of other worlds. Here, we review the status of the mission concept, discuss the key mission parameters, and outline the trade-offs related to the mission’s architecture. In preparation for an upcoming concept study, we define a mission baseline based on a free-formation flying constellation of a double Bracewell nulling interferometer that consists of 4 collectors and a central beam-combiner spacecraft. The interferometric baselines are between 10–600 m, and the estimated diameters of the collectors are at least 2 m (but will depend on the total achievable instrument throughput). The spectral required wavelength range is 6–16 μm (with a goal of 4–18.5 μm), hence cryogenic temperatures are needed both for the collectors and the beam combiners. One of the key challenges is the required deep, stable, and broad-band nulling performance while maintaining a high system throughput for the planet signal. Among many ongoing or needed technology development activities, the demonstration of the measurement principle under cryogenic conditions is fundamentally important for LIFE.

Reflectance spectroscopy is a technique widely used to investigate the composition and physical properties of a surface. The spectro-polarimetry adds the investigation of the polarimetric state of the light, while keeping the spectroscopy dependency. This technique is currently limited for the characterization of the surface, but can bring another clue on the composition and physical properties of the studied surface. We present here the design of a novel ellipsometer, optimized for the investigation of the polarization state of the light reflected by a granular surface. This instrument is able to measure the linear and circular components of the polarization over a wide spectral range from the ultraviolet to near-infrared and at a wide choice of geometrical configuration. The wide spectral range is achieved with the use of a photoelastic modulator acting like a retardance waveplate over the whole working range. Spectro-polarimetric investigations of terrestrial and extra-terrestrial samples will have application to mineralogical investigations, planetary surface explorations, and improve our understanding of the Solar System.

This paper presents a comprehensive analysis of Class-E series-tuned radio-frequency power amplifiers (RFPAs), focusing on their design and optimization for high efficiency and performance. However, achieving optimal performance involves navigating trade-offs among efficiency, bandwidth, harmonic suppression, output power capability, and device stress. This work examines the trade-offs involved in the series-tuned ((Formula presented.)) network and establishes the bounds for its quality factor using computer-aided harmonic balance (HB) simulations. Additionally, it explores optimal harmonic termination strategies to enhance the performance and efficiency of the design. Finally, a novel methodology using harmonic termination is proposed, simplifying the design process by eliminating the need for traditional load-pull extraction methods.

NOTT (formerly Hi-5) is the L’-band (3.5-4.0μm) nulling interferometer of Asgard, an instrument suite in preparation for the VLTI visitor focus. The primary scientific objectives of NOTT include characterizing (i) young planetary systems near the snow line, a critical region for giant planet formation, and (ii) nearby mainsequence stars close to the habitable zone, with a focus on detecting exozodiacal dust that could obscure Earthlike planets. In 2023-2024, the final warm optics have been procured and assembled in a new laboratory at KU Leuven. First fringes and null measurements were obtained using a Gallium Lanthanum Sulfide (GLS) photonic chip that was also tested at cryogenic temperatures. In this paper, we present an overall update of the NOTT project with a particular focus on the cold mechanical design, the first results in the laboratory with the final NOTT warm optics, and the ongoing Asgard integration activities. We also report on other ongoing activities such as the characterization of the photonic chip (GLS, LiNbO3, SiO), the development of the exoplanet science case, the design of the dispersion control module, and the progress with the self-calibration data reduction software.

Asgard/NOTT (previously Hi-5) is a European Research Council (ERC)-funded project hosted at KU Leuven and a new visitor instrument for the Very Large Telescope Interferometer (VLTI). Its primary goal is to image the snow line region around young stars using nulling interferometry in the L′-band (3.5 to 4.0) μm, where the contrast between exoplanets and their host stars is advantageous. The breakthrough is the use of a photonic beam combiner, which only recently allowed the required theoretical raw contrast of 10-3 in this spectral range. Nulling interferometry observations of exoplanets also require a high degree of balancing between the four pupils of the VLTI in terms of intensity, phase, and polarization. The injection into the beam combiner and the requirements of nulling interferometry are driving the design of the warm optics and the injection system. The optical design up to the beam combiner is presented. It offers a technical solution to efficiently couple the light from the VLTI into the beam combiner. During the coupling, the objective is to limit throughput losses to 5% of the best expected efficiency for the injection. To achieve this, a list of different loss sources is considered with their respective impact on the injection efficiency. Solutions are also proposed to meet the requirements of beam balancing for intensity, phase, and polarization. The different properties of the design are listed, including the optics used, their alignment and tolerances, and their impact on the instrumental performances in terms of throughput and null depth. The performance evaluation gives an expected throughput loss <6.4% of the best efficiency for the injection and a null depth of 1/42.10-3, mainly from optical path delay errors outside the scope of this work.

The Ultraviolet Imager (UVI) is a challenging instrument developed in the frame of the SMILE mission, a collaboration between ESA and CAS. The UVI instrument is a CMOS-based ultraviolet camera developed to image Earth's northern auroral regions. It is centered on the 160-180 nm UV waveband, with a 10° × 10° field of view. At the core of the instrument, four thin film-coated mirrors guide light into its detector and ensure most of the signal filtering, crucial to achieve an out-of-band rejection ratio as low as possible to reject light from solar diffusion, dayglow and unwanted atomic lines. We developed an interferometric coating based on an MgF2/LaF3 multilayer stack deposited by ion-assisted electron-beam deposition. We gradually improved our evaporation setup to reach a high degree of homogeneity, precision and repeatability on the material thicknesses, over the entire mirrors surface. The reflectivity maximum is above 85% and the wavelength at which it occurs is adjustable within 1 nm, while the out-of-band reflectivity between 120 and 155 nm and between 200 nm and 1100 nm is kept below 6% on average never exceeding 8 %. The coating has been space qualified and shows stable performances in conditions representative of the instrument operation environment (thermal cycling under vacuum, radiations, UV exposure…).

Intersatellite optical communication links will be crucial for the development of future global optical and quantum communication networks. Under the harsh space environment satellite optical terminals will suffer pointing jitter and wavefront errors. In this paper, the impact of the combination of these errors on the transmitter side is modeled. Combining the far-field diffraction patterns obtained through computational Fourier optics and the statistics of the pointing jitter, the received power statistics are derived numerically for different scenarios. The computational model is first used to evaluate the optimum nominal parameters of the transmitted beam. Then, several optical aberrations are added to the transmitted beam and their impact on the communication performance is evaluated through the average bit error rate.

During the last few years, one of our main research topics has been developing a new type of spectropolarimeter intended for space applications. Initially analyzed numerically, the instrument has a compact, stable design without rotating components. The entire Stokes vector can be determined in a single shot in a vast spectral range. The simulations proved that the modulation schemes that can be obtained for this instrument are close to the optimal form. The objective of the current research is the experimental validation of this instrument. Here, we present the first results for determining the instrumental matrix and the demodulation results for a s eries of polarization states. In conclusion, we present the possible further developments of that project.

Acousto-Optical Tunable Filters (AOTFs) are a promising technology, exceptionally suited for advanced applications in spectroscopy and imaging across various scientific fields, including space exploration. This is due to their flexibility and high-speed functionality for precise wavelength selection via periodic modulation of the crystal’s refractive index using sound waves. These AOTFs are in turn driven by Radio Frequency (RF) signals through a transducer creating sound waves inside the crystal. This work presents a detailed comparison of three distinct topologies of Radio Frequency Power Amplifiers (RFPAs) for driving these AOTFs within the 30 to 300 MHz frequency range. The analysis focuses on three critical parameters: efficiency, bandwidth, and linearity, which are essential for optimizing the performance of AOTFs. By evaluating the trade-offs among these parameters, this research aims to identify the most effective design approach for RFPAs in this application context.

One of the most ambitious goals of modern astronomy is to uncover signs of extraterrestrial biological activity, primarily achieved through spectroscopic analysis of light emitted by exoplanets to identify specific atmospheric molecules. Most exoplanets are indirectly identified through techniques like transit or Doppler shift of the host star's flux. Long-term surveys have yielded statistical insights into the occurrence rates of different planet types based on factors such as radius/mass, orbital period, and the spectral type of the host star. Initial estimates of terrestrial planets within the habitable zone have also emerged. However, the difficulty of detecting light from these exoplanets leaves much unknown about their nature, formation, and evolution. As the number of rocky exoplanets around nearby stars rises, questions about their atmospheric composition, evolutionary trajectory, and habitability increase. Direct measurement of an exoplanet's atmospheric composition through its spectral signature in the infrared can provide answers. Measuring the infrared spectrum of these planets poses significant challenges due to the star/planet contrast and very small angular separation from their host stars. Previous research showed that space-based telescopes are mandatory, and unless large primary mirrors (>30m in diameter) can be sent into space, interferometric techniques become essential. Combining light from distant telescopes with interferometric techniques allows access to information at minimal angular separation, operating within the diffraction limit of individual telescopes. Successful demonstrations of on-ground nulling interferometry open a new era for such space-based missions. They are vital to sidestep and tackle these scientific questions. We recently initiated a new study with the European Space Agency to explore the design parameters and the performances related to an interferometric concept based on a single spacecraft and sparse multiple sub-apertures. Launch constraints are linked to the use of an Ariane 6 launch vehicle. Our parametric study covers a range of 1-4 m for the diameter of the telescope and a 10-60 m baseline. The most promising concept working in the infrared range (3-20μm) will be highlighted. This study is conducted by TUDelft in cooperation with KULeuven, CSL/ULiège, and Amos with the support of the European Space Agency.

This paper proposes a novel approach to improve the performance of free-space optical communication intersatellite links by combining fundamental Gaussian and higher-order Laguerre-Gaussian beams. We present a comprehensive mathematical model to analyze the system’s performance, including received power statistics, average bit error probability, and outage probability. To generate the desired beam profiles, we propose an optical system capable of creating a superposition of orthogonally polarized Laguerre-Gaussian beams that yield the far-field irradiance distributions that optimize the communication performance. Our theoretical analysis demonstrates that the combination of fundamental Gaussian and higher-order modes can significantly enhance system performance compared to conventional fundamental Gaussian beams. In some scenarios, the proposed approach offers savings on the order of 20% to 40% of the required transmitted power.

We describe the state of the development of a coherence scanning interferometer to measure local changes in topology and local induced vibrations of a mirror at cryogenic temperatures. The metrology instrument incorporates an optical phase mask and a microlenses array, enabling the acquisition of complete white light interferograms within a single-camera frame. This stands in contrast to traditional temporal phase-shifting interferometers. We design the optical phase mask as a combination of steps of different thicknesses, so each step introduces a different optical path difference to the rays. The local interferograms for each camera frame provide us with information on the local topology of the mirror. The interferogram displacement between camera frames allows us to monitor the mirror’s local induced vibrations. In this work, we report the metrology instrument’s working principle through numerical simulations and present the latest results of a proof of concept developed at the laboratory. The metrology instrument shown is of extensive usability in diverse applications related to real-time measurements of various fast physical processes and real-time characterization of the optical components topology.