Fresnel reflections at interfaces resulting from optical-index discontinuities reduce the transmission efficiency of optical components. Conventional single-layer antireflection coatings can mitigate Fresnel reflections; however, their performance is constrained by narrow operational bandwidth, angular sensitivity, and optical material availability. Multilayer antireflection coatings enable greater flexibility in optical-index matching and broader spectral performance, although they introduce greater fabrication complexity, higher cost, and additional process-control challenges. This dissertation investigates pseudo-randomly distributed nanostructure surfaces (PDnS) as an alternative antireflection solution for optical flats, focusing on optical design and numerical analysis, fabrication feasibility, and experimental performance validation. Pseudo randomly distributed nanostructured surfaces are engineered to redistribute incident optical energy into multiple diffraction orders, by precisely controlling multiple phase transitions within periodic unit cells. PDnS with specific diffraction characteristics were designed and numerically evaluated for spectral transmission enhancement in the axial propagation direction, off-axis scatter reduction, and reflectivity suppression. The design study investigated the effects of unit-cell phase profiles and scales, binary phase thicknesses, air-substrate optical index contrast, total integrated scatter suppression in reflection and transmission, and fabrication complexity. Proof-of concept test structures were fabricated on silicon and sapphire optical flats using a photoresist two-photon polymerization process. The resulting structures were characterized by confocal optical profilometry, and their spectral performance was evaluated using spectroscopy, ellipsometry, and scatter measurements. Experimental results demonstrate that the fabricated PDnS designs enhance axial transmission across a broad wavelength range at both normal and oblique incidence angles, without sub wavelength period restrictions. Under equivalent fabrication critical-dimension constraints, conventional gratings achieve higher axial transmission for polarized light, but only over a limited range of incidence angles, and are very sensitive to fabrication fidelity. Greater design stability, fabrication tolerances, and reduced fabrication times relative to conventional gratings are demonstrated for PDnS. Fabrication imperfections such as stitching defects and height nonuniformities introduce minimal scatter, with low impact on design performance. Optical polarization effects due to the presence of PDnS on the substrate surfaces are also investigated.
