Research on the application of dielectric films in large aperture astronomical telescopes

Large aperture telescope mirrors require reflective films with higher reflectivity to improve their optical efficiency and better stability to maintain their reflective performance. In this paper, an enhanced aluminum reflective film was deposited on a 2.5-meter mirror using ion beam-assisted deposition technology in a 3.2-meter coating equipment. Through the enhancement of the reflective performance of the aluminum reflective film by the dielectric film, the average reflectivity of the aluminum reflective film was improved to 91.3% within the 350-1700 nm wavelength range, and the reflectivity of the three working wavelength bands was increased to 95%. A full-dielectric reflective film was deposited on a 1.7-meter mirror, and the average reflectivity in the full aperture range of 1010-1090 nm was greater than 99.8%. After testing, the reflective mirror coated with the outermost dielectric film exhibited good friction resistance, and the dielectric film itself possessed excellent environmental stability. Applying it to the surface of metal films can effectively reduce the contact between metal films and the external environment, thus slowing down the degradation of the reflective film's performance. Dielectric films can improve the reflectivity of metal films and enhance the overall environmental stability of the reflective film, making them highly suitable for use in large aperture telescope mirrors.