Multilayer resonant subwavelength gratings: effects of waveguide modes and real groove profiles.
The boundary integral equation code PCGrate-S(X) is used to analyze diffraction on Hubble Space Telescope Cosmic Origins Spectrograph gratings at different boundary shapes and layer thicknesses. An effect of resonance anomalies excited in nonconformal dielectric layers overcoated on the surface of metallic grating on the efficiency is studied for the first time to our knowledge. Refractive indices (RIs) for bulk MgF2 taken from well-known references are found to be not suitable for thin optical layers at wavelengths between 115 and 170 nm. A method based on scale fitting of calculated and measured grating efficiencies is outlined for derivation of thin-film optical constants at hard to measure wavelengths. The calculated efficiency based on real boundary profiles and derived RIs of the G185M subwavelength grating is shown to fit within 9.6% or better to the measured data.
International Intellectual Group, Incorporated, PO. Box 335, Penfield, New York 14526, USA. lig@pcgrate.com
Leonid I
LI
Goray
Ivan G
IG
Kuznetsov
Sergey Yu
SY
Sadov
David A
DA
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