All dielectric reflective films use the principle of optical interference to select two types of dielectric materials that have high and low refractive index characteristics respectively. These films are stacked with multiple high- and low-refractive-index materials to achieve wide-band, high-reflectivity targets. According to the performance requirements of the film layer, the typical all-dielectric reflective film system design contains tens or even hundreds of thin films. Compared with the traditional metal mirror, the all-dielectric mirror has the advantages of long service life, low absorption of the film layer, and high reflection efficiency within the reflection band. From the process point of view, all medium reflective films have high requirements for monitoring the uniformity of equipment film layers. In the case of relatively large mirror apertures, film stress control is also very important. Otherwise, it is difficult to achieve high-precision high-precision optical mirror applications.
The researchers of the large-aperture optical technology research institute of the Nanjing Astronomical Optical Technology Research Institute of the National Astronomical Observatory of the Chinese Academy of Sciences aimed at the application requirements of the astronomical optical telescope. After technical research, new advances have been made in the development of the all-dielectric membrane system. Currently, all-medium reflective films have been successfully deposited for the blue zone camera of the LAMOST spectrometer in the Datian District. The spectral reflectance is better than 97.6% in the 350 nm to 590 nm range. The performance is significantly higher than that of the silver film. The reflectance; The results show that after the coating can maintain a very high surface accuracy, measured before the coating shape measurement results RMS values ​​were 0.0149λ and 0.0135λ (λ = 632.8nm).
The total number of layers of the blue zone total dielectric mirror film is more than 50 layers, and the service life is expected to increase to more than 5 years. The original silver mirror mirror was only 2 years old. The mirror was sent to the Xinglong Astronomical Observatory of the National Astronomical Observatory where the LAMBS telescope was located at the end of January 2015 for actual observation to further test its performance. After successful, the mirror will gradually replace the silver plated mirror in the blue area of ​​the spectrometer to reduce maintenance. Workload.
Next, Nanjing Tianguang Institute will also conduct the development of a red zone all-dielectric mirror of the LAMOST spectrometer, and explore the feasibility of a full band (360-900 nm) all-dielectric mirror coating.
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