Proceedings Article | 1 February 1991
KEYWORDS: Optical filters, Carbon, Visible radiation, Aluminum, Extreme ultraviolet, Telescopes, Multilayers, Ultraviolet radiation, Absorption, Tellurium
The multilayer mirrors used in the nonnal incidence optical systems of the Multi-Spectral Solar Telescope Array
(MSSTA) are efficient reflectors for soft x-ray/extreme ultraviolet (EUV) radiation at wavelengths that satisfy the Bragg
condition, thus allowing a narrow band of the soft x-rayfEUV spectrum to be isolated. However, these same mirrors are also
excellent reflectors in the visible, ultraviolet, and far ultraviolet (FUV) part of the spectrum, where normal incidence
reflectivities can exceed 50%. Furthermore, the sun emits far more radiation in the ultraviolet and visible part of the spectrum
than it does in the soft x-rayIEUV. For this reason, thin foil filters are employed to eliminated the unwanted longer
wavelength solar emission. With the proper choice of filter materials, the filters can also be used to eliminate EUV radiation
at longer wavelengths, where the increasing specular reflectivity of multilayer mirrors and the high intensity of solar
emissions can cause "contamination" of the image in the narrow band defined by the Bragg condition. In addition, filters can
eliminate higher order multilayer reflections. Finally, filter absorption edges can sometimes be utilized to reduce the width of
the primary bandpass. The MSSTA instrument uses various combinations of thin foil filters composed of aluminum, carbon,
tellurium, potassium bromide, beryllium, molybdenum, rhodium, lexan, and phthalocyanine to achieve the desired radiation
rejection characteristics. The filters are currently being manufactured by Luxel Corporation of Friday Harbor, Washington, and
Penn-Spectra Incorporated of Wallingford, Pennsylvania. This paper discusses issues concerning the design, manufacture, and
performance of the MSSTA filters.
