Multilayer Optics for Ultra-high Resolution Solar Imaging in the EUV Region

Details Multilayer Optics for Ultra-high Resolution Solar Imaging in the EUV Region Multilayer Optics for Ultra-high Resolution Solar Imaging in the EUV Region

May 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003spd....34.2406s&link_type=abstract

American Astronomical Society, SPD meeting #34, #24.06; Bulletin of the American Astronomical Society, Vol. 35, p.853

Physics

Optics

Scientific paper

Highly reflective multilayer-coated optics operating at near-normal incidence angles have been the enabling technology for solar imaging instruments in the extreme ultraviolet (EUV) energy range. Despite the advances made in recent years towards understanding of solar processes through missions such as TRACE, major unresolved questions in solar physics still remain, for instance on the subjects of coronal heating, eruptive flare and coronal wind initiation. Future generations of missions will need to study the physics of hot magnetized plasmas that occur in the corona on extremely small spatial and temporal scales, requiring imaging instruments with extremely high resolution and large fields of view. Proposals for future solar missions require optics with diameters up to 700 mm and system wavefront errors as low as 0.4 nm.
Experimental results will be presented for normal-incidence, four-mirror and two-mirror EUV cameras operating around 13.4 nm. Mirror substrates were manufactured by commercial vendors and achieved figure errors around 0.25 nm rms, verified by phase-shifting, point-diffraction visible light interferometers developed at Lawrence Livermore Lab. The optics were multilayer-coated aligned and tested at facilities at Lawrence Livermore and Lawrence Berkeley National Labs. A large-scale DC-magnetron sputtering tool is used to coat the optics and can accommodate multiple optics up to 600 mm in diameter in a single deposition run. During multilayer deposition, a velocity modulation algorithm is applied in order to achieve extremely precise film thickness control. The deposited Mo/Si coatings demonstrate added figure errors below 0.05 nm rms. While these systems were constructed for EUV lithographic applications, the experimental results are immediately applicable to astronomical x-ray optics. Currently these are the only multilayer-coated EUV cameras worldwide meeting such stringent specifications, and have been implemented in the construction of the first large-field, diffraction-limited EUV imaging systems. In addition to Mo/Si coatings that are applicable for wavelengths longer than the Si L2,3 edge (12.5 nm), other multilayer material combinations have been developed for shorter wavelength bands such as the less studied 8-12 nm region where emission lines of ionized elements (such as Fe XVIII, Fe XIX and Fe XX) occur.
This work was performed under the auspices of the U.S. Department of Energy. Funding was provided by EUV LLC under a Cooperative Research and Development Agreement. Partial support has also been provided by the Naval Research Laboratory.

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