Anti-Reflection Coatings on 3D-Printed Components

The use of anti-reflection coatings on 3D-printed components to reduce both Fresnel reflections and scattering is explored. Two similar photo-initiated acrylic commercial material structures, known as Standard Clear (SC: T~60% @ λ = 800 nm) and VeroClear (VC: T~90% @ λ = 800 nm), used specifically for optical components, are examined. The refractive indices for slab samples~(5 × 5 × 0.7) cm are measured at λ = 650 nm and averaged over the slab area: n(SC)~(1.49 ± 0.04) and n(VC)~(1.42 ± 0.03). Within experimental error, novel Shore D mapping is used to show hardness distribution across the surface flats, with VC slightly harder than SC, where VC = 85.9 ± 0.3 and SC = 84.4 ± 1.3, indicating uniform hardness. A TiO2/MgF2 anti-reflection twin-layer coating is deposited onto one side of an unpolished SC slab and binds well, passing standard peeling and humidity tests. Shore hardness increases to SCCOATED = 87.5 ± 1.5. It is found to reduce the measured Fresnel reflection and surface scatter by~65% without requiring major polishing, paving the way for lower-cost high-quality optics. The demonstration of successful anti-reflection coatings will benefit all 3D-printed component finishes, permitting viable film deposition more broadly.

The Forensic Utility of Photogrammetry in Surface Scene Documentation

Outdoor crime scene documentation needs to be accurate and precise to preserve evidence. Photogrammetry is a potential option. Structure from Motion (SfM) processes photographs into 3D models. As commercial software does not disclose this process, this documentation technique could be legally inappropriate. A potential solution to this problem is open-source software. A series of mock outdoor crime scenes were documented using SfM and total station mapping. Ten large surface scatter scenes containing plastic human remains and personal objects were laid out in 10 × 10 m units in a New England forested environment. The small surface scatter scenes consisted of a pig (Sus scrofa) mandible placed in different environments. The resulting models were built using PhotoScan by AgiSoft and MicMac by IGN. Accuracy was measured by the amount of variance in fixed-datum measurements, whereas visual qualitywas determined by comparison. The average total variance in fixed-datum lengths for six of the ten scenes was below 0.635 cm. The maximum differences in measurement between the total station and software measurements were 0.0917 m (PhotoScan) and 0.178 m (MicMac). Comparative histograms had low standard deviations and mean distances between points. Conditions such as light, ground foliage and topography affect model quality. This research shows that SfM has the potential to be a rapid, accurate and low-cost resource, but there are limitations that must be considered.

Direct dating of lithic surface artifacts using luminescence

Archaeological surface assemblages composed of lithic scatters comprise a large proportion of the archaeological record. Dating such surface artifacts has remained inherently difficult owing to the dynamic nature of Earth-surface processes affecting these assemblages and because no satisfactory chronometric dating technique exists that can be directly applied to constrain the timing of artifact manufacture, discard, and thus human use of the landscape. Here, we present a dating approach based on optically stimulated luminescence (OSL)—OSL rock-surface burial dating—and apply it to a lithic surface scatter in Tibet. We generate OSL burial ages (age-depth profiles) for each artifact, outline the methodological complexities, and consider the artifact burial ages in the context of local-scale Earth-surface dynamics. The oldest age cluster between 5.2 and 5.5 thousand years is likely related to quarrying activities at the site and thus represents the oldest chronometric age constraints for human presence on the south-central Tibetan plateau.