Innovative Optical Filters for EUV Coronal Spectroscopy

Understanding the mechanisms driving coronal heating remains a long-standing challenge in solar and stellar physics. To shed light on this complex topic, upcoming EUV spectroscopy solar observatories, such as the future NASA MIDEX mission MUSE (Multi-slit Solar Explorer), are being developed to drive the modeling of the solar corona dynamics. Within the framework of MUSE, we are actively engaged in the development of novel carbon nanotube (CNT)-based optical blocking filters. These utilize CNT pellicles coated with aluminum or zirconium as complementary band-passing elements in the EUV range of interest to MUSE, targeting wavelengths between 10 nm and 31 nm. The use of highly EUV-transparent CNT pellicles to support the thin metal coatings offers the advantage of eliminating tightly spaced meshes prone to diffraction artifacts (such as those observed in the Solar Dynamics Observatory SDO and the Atmospheric Imaging Assembly AIA). By adopting an integrated CNT structural mesh with a larger pitch of approximately 5 mm to support the thin CNT pellicle, our filters aim to minimize diffraction artifacts while maximizing EUV transmittance. To evaluate the performance of these novel filters, we conducted a series of optical and mechanical characterization tests. Here we report results from UV, Vis, and NIR spectroscopy performed at UNIPA/INAF and vacuum-Ultraviolet and X-ray Absorption Spectroscopy (UAS-XAS) measurements performed at synchrotron facilities. We will present the data acquisition and analysis that allowed us to successfully characterize the experimental EUV transmittance properties of such filters. Furthermore, we make a comparative analysis between the performance of our new technology filters and existing filters from SDO and AIA. The outcomes of this study will aid in filter testing, modeling, and design optimization specifically tailored for the aforementioned NASA MUSE mission and other future EUV solar physics experiments....