Evaluation of microhardness and scratch testing for optical coatings

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Abstract
Microhardnesstesting was evaluated and compared to abrasion testing for a variety of optical coatings. The microhardness testers were used for both microhardness and scratch testing. The thin dielectricoptical coatings required very light deadweight loads (2–50 g), low background vibration levels, and, to minimize penetration depth, the use of Knoop diamond indentors. In addition to single layer films of TiO2, a variety of good and bad (as determined by eraser rub testing)multilayercoating products were used in this comparison. In all cases the microhardness tester confirmed the ranking of the eraser rub tests. However, not only was microhardnesstesting more quantitative and less subjective, but it was also able in many cases to distinguish between hardness and adhesion failures. In addition, microhardness tests showed some promise for predicting the cutting yields on uncoated flat glass substrates.

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