EUV mutlilayer coatings for Solar-C

Solar-C is about to be the next generation of satellite observatory following the successful Hinode mission launched in September 2006 [1]. The aim of the Solar-C project is to reach unprecedented high-resolution imaging and spectroscopic observations to resolve fundamental interactions that will give a better understanding of the solar corona origins and activity. The development of the on-board extreme ultraviolet spectrometer (EUVST) is challenging as the shape, the curvature and the multilayer coating of the diffraction grid requirements are dependent on EUV cutting-edge technology. Based on the recent development of the Extreme Ultraviolet Imager onboard Solar Orbiter [2] ESA mission (scheduled for launch in February 2020), we propose a three-material aperiodic coating with a high efficiency in the 17 to 21 nm wavelength range for the Solar-C spectrometer. At first, Al/Mo/SiC multilayer coatings have been successfully developed and optimized as single-band (periodic) and dual-band (bi-periodic) mirrors in order to reflect the Fe 17.1 nm line and/or the He II line 30.4 nm [3], [4]. For the EUVST instrument, we propose a new Al/Mo/SiC design with an aperiodic structure that fulfill the requirements in terms of high efficiency and broad bandpass. We will discuss about the next challenging steps of development and characterization of this design on flat substrates, and on diffraction grating similar to the one to be used in EUVST spectrometer.

[1] J. L. Culhane et al., “The EUV Imaging Spectrometer for Hinode,” Solar Physics, vol. 243, no. 1, pp. 19–61, Sep. 2007. [2] P. Halain et al., “The extreme ultraviolet imager of solar orbiter: optical design and alignment scheme,” in Proc. SPIE, Optical Engineering + Applications, San Diego, United States, 2015, vol. 9604, p. 96040H. [3] E. Meltchakov et al., “Development of Al-based multilayer optics for EUV,” Appl. Phys. A, vol. 98, no. 1, p. 111, Jan. 2010. [4] F. Delmotte et al., “Development of multilayer coatings for solar orbiter EUV imaging telescopes,” in Proc. SPIE, Solar Physics and Space Weather Instrumentation V, San Diego, United States, 2013, vol. 8862, p. 88620A.