Uniform high-reflectivity silver film deposited by planar magnetron sputtering

Following the development of various complex optical elements, especially those involving aluminum alloys with several free-form surfaces, it is critical to understand the material coating methods. This report provides guidance for coating aluminum alloy optical elements containing four free-form surfaces with reflective silver films. To determine a proper film deposition thickness with high reflectivity applied by magnetron sputtering, a model is proposed to explain how the reflectivity is affected by the thickness of the silver film on the aluminum alloy substrates. Additionally, to optimize the uniformity of film thickness deposited from a magnetron source, a more accurate distribution model was developed by introducing gas pressure parameters. This modified model provides excellent agreement between simulated and experimental results. Finally, the film thickness distribution on the optical element integrated with four free-form surfaces is simulated using the modified model, and the influence of the relative position of sources and substrates on the film thickness uniformity is explored.