X-ray and XUV optics for space telescopes (Orale)
Abstract
One of the pioneers in coatings for optics in the extreme ultraviolet (EUV) spectral range (typically 10 to 60 nm), the "XUV Optics" team of Laboratoire Charles Fabry (LCF) study and optimize interferential mirrors based on multilayers for several applications since more than 25 years. Today, the main applications are related to the observation of the solar corona in astrophysics, optics for new x-ray sources (X-ray lasers, High Harmonics Generation Sources, Free Electron Lasers), optics for ultrashort pulses (attosecond science) or diagnostics of hot plasmas. After a brief introduction on the history of EUV multilayer mirrors and solar corona imaging, we will present recent results achieved at LCF. Periodic Mo/Si multilayers have been extensively studied and used since more than 20 years. Some years ago, we have been able to increase the reflectivity in the wavelength range 20 nm to 40 nm by adding a third material in the periodic structure [1]. Such B4C/Mo/Si multilayers have been designed for imaging the HeII emission line of the Sun (at 30.4nm) and have been deposited on EUV imager of HECOR mission [2]. By using a superposition of two periodic multilayers with three materials per period, we have designed dual channel mirrors [3, 4] that will be deposited on the EUV telescopes of Solar Orbiter (ESA mission). Moreover, we have recently shown that the use of Al instead of Si in periodic multilayer structure allows increasing mirror performances [5] (see figure). We will compare the results obtain with multilayer mirrors deposited by ion beam sputtering or magnetron sputtering. Reflectivity higher than 50% at 17 nm have been measured on synchrotron radiation source with SiC/Mo/Al structures. These results have required a systematic optimisation of deposition parameters in order to obtain aluminium thin films with low interfacial roughness. [1] J. Gautier et al., Applied Optics 44, 384 (2005) [2] Frédéric Auchère et al., Proc. SPIE 6689, 66890A (2007) [3] J. Gautier et al., Optics Communications 281, 3032 (2008) [4] C. Hecquet et al., Appl Phys A 95, 401 (2009) [5] E. Meltchakov et al., Appl Phys A 98, 111 (2010)