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Random antireflection nano-structured surfaces (ARS) have been studied for their broadband antireflection (AR) properties and polarization insensitivity. ARS are designed and modeled using effective medium approximations (EMA) as thin layers of the desired effective permittivity through a global density average, independent of surface feature distributions. To study the AR efficiency of varying transverse feature distributions of ARS on optical surfaces, we methodically simulated and analyzed the performance of pseudo-random deterministic Dammann gratings, acting as a quarter-wave-thickness AR overcoating on a functional binary 50% duty cycle test grating, using rigorous coupled wave analysis. We chose a fused silica dielectric substrate, numerically simulated at normal incidence conditions for both polarizations at 633nm wavelength. The study parameters consisted of Dammann gratings of different orders for evanescent diffraction control, chosen to have effective permittivities comparable to predicted EMA requirements to match AR efficiency, varying periodic scales, and distinct surface distribution autocorrelation scales to control the structure factor. The goal is to elucidate the transition of evanescent coupling orders from the Dammann ARS to the functional test grating, without perturbing the original diffractive performance, while it enhances transmitted overall power efficiency. The simulated results exhibit variations in the performance of candidate designs, signifying the importance of surface feature distributions on the overall efficiency of ARS as an effective antireflection treatment for diffractive components. Not only subwavelength periodicity scales, but nearwavelength scales as well show high transmission efficiency without presence of parasitic orders from the base binary test grating, in contrast to EMA design guidelines.
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