Abstract
Suppressing Fresnel reflections from dielectric boundaries using
periodic and random antireflection structured surfaces (ARSSs) has
been vigorously studied as an alternative to thin film coatings for
high-power laser applications. A starting point in the design of ARSS
profiles is effective medium theory (EMT), approximating the ARSS
layer with a thin film of a specific effective permittivity, which has
features with subwavelength transverse-scale dimensions, independent
of their relative mutual positions or distributions. Using rigorous
coupled-wave analysis, we studied the effects of various pseudo-random
deterministic transverse feature distributions of ARSS on diffractive
surfaces, analyzing the combined performance of the quarter-wave
height nanoscale features, superimposed on a binary 50% duty cycle
grating. Various distribution designs were investigated at
633 nm wavelength for TE and TM polarization states at normal
incidence, comparable to EMT fill fractions for a fused silica
substrate in air. The results show differences in performance between
ARSS transverse feature distributions, exhibiting better overall
performance for subwavelength and near-wavelength scaled unit cell
periodicities with short auto-correlation lengths, in comparison to
equivalent effective permittivity designs that have less complicated
profiles. We conclude that structured layers of quarter-wavelength
depth and specific feature distributions can outperform conventional
periodic subwavelength gratings as antireflection treatments on
diffractive optical components.
Subject
Atomic and Molecular Physics, and Optics,Engineering (miscellaneous),Electrical and Electronic Engineering