Optimization of thin-film design for multi-layer dielectric grating

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Optimization of thin-film design for multi-layer dielectric grating
% s6 m. P$ K' x6 b' A8 G4 A/ IAbstract
, v! c$ Y* |& r( g$ UThin-film design used to fabricate multi-layer dielectric (MLD) gratings should provide high transmittance during holography exposure, high
' l- j/ \8 ]3 Rreflectance at use wavelength and sufficient manufacturing latitude of the grating design making the MLD grating achieve both high diffraction
efficiency and low electric field enhancement. Based on a (HLL)9H design comprising of quarter-waves of high-index material and half-waves of
* j9 y0 O2 G5 F4 R4 r, {low-index material, we obtain an optimum MLD coating meeting these requirements by inserting a matching layer being half a quarter-wave of
Al2O3 between the initial design and an optimized HfO2 top layer. The optimized MLD coatings exhibits a low reflectance of 0.017% under
( u5 x* a2 H  o+ ]* P% Nphotoresist at the exposure angle of 17.88 for 413 nm light and a high reflectance of 99.61% under air at the use angle of 51.28 for 1053 nm light.
, I! p7 G1 i9 u6 y# P9 bNumerical calculation of intensity distribution in the photoresist coated on the MLD film during exposure shows that standing-wave patterns are
) [+ \6 F) }" N8 Rgreatly minimized and thus simulation profile of photoresist gratings after development demonstrates smoother shapes with lower roughness.
3 r: x: O5 b, s5 B1 x6 F; LFurthermore, a MLD gratings with grooves etched into the top layer of this MLD coating provides a high diffraction efficiency of 99.5% and a low
4 n5 q$ f) ^  V, C0 n5 Zelectric field enhancement ratio of 1.53. This thin-film design shows perfect performances and can be easily fabricated by e-beam evaporation.
# 2006 Elsevier B.V. All rights reserved.
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