MezzoCielo (or “half of the sky”), novel concept of extremely large field-of-view monocentric optical devices designed to continuously patrol the whole sky, is an optical sphere which requires the filling of its inner volume with special fluid in order to be actually convergent with reasonable focal ratio (for spherical aberration reduction). This fluid has to be characterized by two main properties, namely low refractive index and extremely high transparency in the visible range, but, of course, many other characteristics, such as thermal and chemical stability over time, no toxicity or flammability, compatibility with glass and metals, are also desirable. By virtue of these considerations, two fluorine liquids have been selected: the fluids commercially known as FC-72, perfluorohexane with nd = 1.251 at T = 25°C, and Novec7200, ethoxy-nonafluorobutane with nd = 1.282 at T = 25°C. In this work, the experimental evaluation of their optical properties (refractive index and transparency) in the visible range and in the thermal interval [-10,+25]°C has been carried out in order to verify the data supplied by the manufacturer and to fully characterize their optical behaviour both spectrally and thermally.
The planetary extreme ultraviolet spectrometer (PLUS) is a project funded by the Italian Space Agency focused on the development of an extreme (EUV) and far-ultraviolet (FUV) high-performance spectrograph, which adopts a dual channel optical scheme. Thanks to an optimized layout based on the use of variable line space (VLS) gratings in an off-Rowland configuration, high spectral and spatial resolution are achieved. The efficiency improvement is obtained by the optimization of the coatings on the optical components. Improved detection limit, shorter observations integration time and unprecedented performance in terms of dynamic range will be achieved by the use of high resolution/dynamic range solar blind photon counting detectors. The photon counting detectors will be based on a micro-channel plate (MCP) coupled with an application specific integrated circuit (ASIC) read out system.
A systematic characterization of optical coatings for space application has been carried out to evaluate the performance drop upon low energy protons, ions exposure. This systematic investigation was supported by a project funded by the European Space Agency. Single layers and bi-layers for visible and near-infrared applications have been irradiated with different ions energies and fluences. Moreover, since the irradiation experiments have been performed in large-scale facilities also the flux has been used as a parameter, selecting some values that were a good compromise between the facility occupation time and the real irradiation conditions faced during a space mission. In this work, a summary of the obtained results is reported. Results show that the performance drop is highly dependent on the fluence and the implantation energy, while only for some materials the flux seems to have an effect.
Spectroscopic observations in the vacuum (VUV, 115-200 nm) and extreme ultraviolet (EUV, 40-115 nm) is of fundamental importance in solar physics, in the physics of interstellar medium, in the study of planetary exospheres. The PLUS project is focused on the development of a high performance spectrograph for the observations of planetary exospheres in the 55-200 nm range. The instrument layout is based on a two channels (VUV/EUV) design. It will be characterized by improved detection limit, shorter observations integration time and unprecedented performance in terms of dynamic range. Such characteristics will be obtained thanks to the development and combination of two key technologies: high efficiency optical components optimized for each channel and high resolution/dynamic range solar blind photon counting detector. The photon counting detector will be based on a Micro-Channel Plate coupled with ROIC ASIC read out system.
A systematic characterization of dielectric coatings for space application is carried out to evaluate the performance drop upon protons exposure. Different energy levels and fluence values are tested. Also, since the irradiation experiments are performed in large scale facilities, different flux rates are tested to establish the operational parameters that better mimic the real irradiation conditions. The induced damage associated with each irradiation session is characterized for a selection of single and bi-layer coatings. Results show that the performance drop is highly dependent on the fluence and the implantation energy.
Multilayer (ML) coatings are a crucial technology for the development of EUV and SXR solar instrumentation, as they represent the only viable option for the development of high-efficiency normal incidence mirrors in such spectral range. However, the current standard MLs are characterized by a very narrow spectral band which is incompatible with the science requirements expected in the next generation of solar instruments. Nevertheless, recent advancement in ML technology has made the development of non-periodic stacks repeatable and reliable, enabling the manufacturing of mirrors with either multi-band or broad-band high efficiency. In this work, after briefly reviewing the state-of-the-art ML coatings for the EUV/SXR range, we investigate the possibility of using non-periodic stacks for the development of multiband and broad-band normal-incidence mirrors to be used in the next-generation missions.
KEYWORDS: Mirrors, Space telescopes, Space mirrors, Space operations, X-ray telescopes, X-rays, X-ray optics, Ultraviolet radiation, Space observatories, Rockets
Mirrors are a subset of optical components essential for the success of current and future space missions. Most of the telescopes for space programs ranging from Earth Observation to Astrophysics and covering all the electromagnetic spectrum from X-rays to Far-Infrared are based on reflective optics. Mirrors operate in diverse and harsh environments that range from Low-Earth Orbit, to interplanetary orbits and the deep space. The operational life of space observatories spans from minutes (sounding rockets) to decades (large observatories), and the performance of the mirrors within the optical system is susceptible to degrade, which results in a transient optical efficiency of the instrument. The degradation that occurs in space environments depends on the operational life on the orbital properties of the space mission, and it reduces the total system throughput and hence compromises the science return. Therefore, the knowledge of potential degradation physical mechanisms, how they affect mirror performance, and how to prevent it, is of paramount importance to ensure the long-term success of space telescopes. In this brief review paper we report an overview on current mirror technology for space missions with a particular focus on the importance of degradation and radiation resistance of the coating materials.
Optical coatings and materials need to be qualified against space environmental agents, such as protons, helium ions and electrons. The induced damage effects are studied in dependence on ion species, energy, flux and fluence. Results show that damages can be dramatically dependent not only by fluence, but also by ions energy, so that qualification should take this factor into account. The significance of results obtained by using gamma-rays in place of ions irradiation to qualify components is briefly discussed. A systematic experimental plan for an extensively study of the irradiation effects induced in a large number of different sample coatings and materials is presented.
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