Stellar in-flight calibration plays a pivotal role in improving the reliability of scientific data acquired by space optical instruments. Changes in sensitivity and performance of the image quality, caused by factors such as optical component degradation or misalignment, can be discovered and tracked by employing in-flight star images and comparing them with on-ground measurements. In this work, we introduce two simulation processes useful for this purpose and apply them to the Metis coronagraph aboard the ESA/NASA Solar Orbiter spacecraft. The first simulation process is a methodology for predicting star visibility in the Field of View (FoV) of the instrument. The second one improves the former code, integrating characteristics on the source, such as star magnitude, and the instrumental features, including reflectivity/transmission of the optical elements, and detector characteristics, e.g. bias, dark current,... The ultimate aim of the simulation is to generate an estimation of the intensity, in Digital Numbers, expected for each pixel of the detector, thus offering valuable insights into the instrument’s response to varying input flux conditions. This innovative approach will provide a comprehensive tool to anticipate and understand the coronagraph’s behavior in response to different celestial scenarios (e.g. from minimum to solar maximum conditions), contributing to more effective in-flight calibrations. Indeed, Metis operates in proximity to the Sun, in a challenging environment marked by high temperatures and significant temperature variations. Although the current results are preliminary, further work is needed to refine and fully understand the simulation outcomes.
The optical constants of titanium dioxide (TiO2) have been experimentally determined at energies in the extreme ultraviolet and soft x-ray spectral regions, from 25.5 to 612 eV. Measuring angle-dependent reflectance of amorphous TiO2 thin films with synchrotron radiation at the BEAR beamline of Synchrotron ELETTRA. The experimental reflectivity profiles were fitted to the Fresnel equations using a genetic algorithm applied to a least-square curve fitting method, obtaining values for δ and β. We compared our measurements with tabulated data. All samples were grown on Si (100) substrates by the electron-beam evaporation technique, with a substrate temperature of 150°C and deposition rates of 0.3 to 0.5 Å/s. Complete films characterization have been carried out with structural (XRD, ellipsometry, and profilometry), compositional (x-ray photoelectron spectroscopy), and morphological (atomic force microscopy) analyses.
A search for novel materials for making multilayers of high reflectivity has been driven by the vigorous demand towards miniaturizing photonics. A typical consumer of high performance multilayers (MLs) is the extreme ultraviolet lithography (EUVL) based on the 13.5 nm laser produced plasma (LPP) source. To sustain “Moore’s law” and print fine features below 10 nm on integrated circuits (IC), source of radiation for the EUVL has to shift towards even shorter wavelengths where 6.x nm wavelength seems to be immediate successor. However, the 6.x nm EUV lithography needs MLs of reflectivity performance above 70 % to support high volume manufacturing (HVM). It is clear that more work is required particularly on the development of MLs with high reflectance, stable to thermal heat and sufficient lifetime. In this work new MLs of B4C/CeO2 are deposited, analyzed and characterized for the first time. Combinations of X-ray reflectometry (XRR) and EUV reflectance measurements near resonance edge of boron are analyzed to derive structural and optical parameters of MLs. ML coatings of B4C/CeO2 MLs have shown similar reflectance performance with the leading candidate MLs around 6.x nm wavelength. Analysis shows that interlayer diffusion is a major reason for low reflectivity performance. Cross-sectional scanning electron microscopy (SEM) images of the MLs have proved formation of interlayer diffusion.
In this work, three TiO2 thin films with thicknesses of 22.7, 48.5 and 102.9 nm were grown on Si (100) substrates by the technique of electron beam evaporation. The films were deposited at a substrate temperature of 150°C with a deposition rate of 0.3 - 0.5 A/sec. The films thicknesses were characterized by spectroscopic ellipsometry and profilometry. The surface roughness was measured by AFM obtaining RMS of less than 0.7nm. Investigations performed by XPS method have shown that stoichiometric TiO2 was obtained on all the samples with no suboxide presences. Reflectance measurements of the samples were performed in EUV and SX spectral regions from 25.5 to 454.2eV using synchrotron radiation. Analyzing the refractive index N=n+ik of TiO2 thin films, optical constants (n,k) in this energy range were both determined by fitting the Fresnel equations with least-square fitting methods.
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