Germanium Lens Surface Roughness: What Ra 5nm Means and How to Achieve It
A germanium lens with Ra 50nm surface roughness will pass an incoming inspection. It will also scatter roughly 0.3–0.5% of incident 10 μm radiation at each surface — enough to reduce thermal imaging system sensitivity by a measurable margin and, in high-power laser applications, to create localized absorption hotspots that degrade the lens over time. […]
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