Abstract
The low expected absorption of Ca in the extreme ultraviolet (EUV) makes it an attractive material for multilayers and filters because most materials in nature strongly absorb the EUV. Few optical constant data had been reported for Ca. In this research, Ca films of various thicknesses were deposited on grid-supported C films and their transmittance measured in situ from the visible to the soft x-rays. The measurement range contains and absorption edges. Transmittance measurements were used to obtain the Ca extinction coefficient . A minimum of 0.017 was obtained at , which makes Ca a promising low-absorption material for EUV coatings. A second spectral range of interest for its low absorption is below the Ca edge at . Measured data and extrapolations were used to calculate the refractive index using Kramers–Krönig relations. This is the first self-consistent data set on Ca covering a wide spectral range including the EUV.
© 2015 Optical Society of America
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