Combinatorial synthesis of BaClF-ReF3 (Re = La, Pr, Er, Sm) layers with graded-index as antireflection coatings in the thermal infrared

• Combinatorial methods were used to search for a robust graded-index layer as antireflection coating in thermal infrared.
• The best antireflection approach for the Ge surfaces can be achieved for the BaClF-LaF3 layer with x = 0.51.
• The optimized characteristics of Gaussian index profile followed by quintic-profile can be obtained in the layers.
• An average refractive index around 1.2 can be carried out as an infrared low-index coating materials.

It is a well-known fact that optical components used in the thermal infrared would be disabled without antireflection coatings due to the serious Fresnel reflections on their surfaces. The antireflection coating consisting of a single inhomogeneous layer with graded-index is an important solution. In our investigation, the combinatorial materials libraries were synthesized to explore the composition dependence of the durability and antireflection characterization of graded-index layers deposited from four rare-earth fluorides LaF3, PrF3, ErF3 and SmF3, admixed with a different amount of BaClF. It was demonstrated that the layers are robust enough to withstand normal handling and environmental conditions, furthermore, the best antireflection approach for the Ge surfaces can be achieved for the BaClF-LaF3 layer with a BaClF concentration x = 0.51, through the high-throughput characterization of the robustness and the spectral transmittance of the elements in the libraries. Because the optimized characteristics of a Gaussian index profile followed by a quintic-profile can be created in the layers, an effective refractive index around 1.2 can be achieved, which is lower than those of infrared low-index coating materials used commonly.

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