| Random anti-reflection surface structures (rARSS) are randomly spaced, densely packed, sub-wavelength cylindrical or conical features that are fabricated on the surface of optical substrates. As light passes from the superstrate to the substrate medium through the rARSS, it propagates in a gradually increasing ratio of glass to air volume fraction, effectively reducing or eliminating Fresnel reflection. Studies found in the literature to date focus on fabricating and testing rARSS on planar substrates, and typically provide normal incidence transmission or reflection measurements over a variable wavelength range. In this work, rARSS are first fabricated on planar fused silica substrates through a metal mask reactive ion etching (RIE) process. Granulometry values, roughness measurements, and spectroscopy data are presented relating the physical characteristics of the gold mask statistical populations, and the resulting rARSS features population, as well as spectral transmission properties of the final surfaces. The rARSS silica fabrication process is attempted on non-vitreous substrates, using three different fabrication methods, and the results are evaluated using spectral transmission measurements, SEM images, and laser confocal microscope images. These results show that the silica rARSS fabrication process is not transferrable to non-vitreous materials. Finally, the rARSS fabrication process for planar fused silica samples is applied to microlens arrays (MLA) of varying aspect ratio, and found to be transferrable. The focal spot of each MLA is measured using a beam profiler and compared to simulated and unprocessed MLA results. Transmission enhancement for rARSS processed MLAs is verified to be comparable to processed fused silica flats, and the propagation characteristics of the beam through focus are shown to be unchanged by the application of the rARSS. Tests are also performed to look at the far-field propagation characteristics of the unprocessed and rARSS processed MLAs by examining their Fourier transforms. It is shown that the rARSS processed MLAs have only slight differences in their far-field diffraction response compared to unprocessed MLAs, indicating that rARSS can be applied to MLAs without negatively affecting the lens' wavefront propagation properties or focusing abilities. |
