An anti-reflection coating for silicon optics at terahertzfrequencies
Gatesman, A.J.; Waldman, J.; Ji, M.; Musante, C.; Yagvesson, S.
Microwave and Guided Wave Letters, IEEE
Volume 10, Issue 7, Jul 2000 Page(s):264 - 266
Digital Object Identifier 10.1109/75.856983
Summary:A method for reducing the reflections from silicon optics at
terahertz frequencies has been investigated. In this study, we used thin
films of parylene as an anti-reflection (AR) layer for silicon optics
and show low-loss behavior well above 1 THz. Transmittance spectra are
acquired on double-sided-parylene-coated, high-resistivity,
single-crystal silicon etalons between 0.45 THz and 2.8 THz. Modeling
the optical behavior of the three-layer system allowed for the
determination of the refractive index and absorption coefficient of
parylene at these frequencies. Our data indicate a refractive index, n,
of 1.62 for parylene C and parylene D, and a reasonably modest
absorption coefficient make these materials a suitable AR coating for
silicon at terahertz frequencies. Coatings sufficiently thick for AR
performance reduced the average transmittance of the three-layer system
by <10% compared to a lossless AR coating with an ideal refractive
index
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