| Aluminum oxide, Al2O3, is a medium index, low absorption material usable for coatings in the near-UV (<300 nm) to IR (9 µm) regions. Typical applications include near-UV laser AR and dielectric mirror designs. Alumina can be used in combination with silicon dioxide layers to form multi-layer structures with high damage thresholds for UV laser applications. Completely oxidized alumina films are absorption-free over the range below 300 nm to at least 5 µm. Slight dissociation and oxygen loss occurs during evaporation. Adhesion is good to glass, most other oxides, some polymers, and to metals such as aluminum and silver. The films generally grow with a crystalline microstructure and low packing density and exhibit index changes when vented to moist air. Adsorption of water is often evident as rings of discoloration which reach a uniform appearance after moisture penetration is complete. This instability effect is exaggerated under low energy evaporation, low substrate temperature, or excessive background pressure evaporation conditions. The refractive index responds to high energy deposition techniques and to high substrate temperature because both parameters decrease the void volume by increasing the packing density of the microstructure. Post-deposition baking in air can also raise the refractive index.Information provided by Materion. |
