The relationship between the diffraction distribution of random metal mesh mesh and the linewidth of the mesh was analyzed by theoretical calculation and FDTD Solutions software simulation. A random-structure metal mesh electromagnetic shielding film with a line width of 5 μm was prepared on a large-aperture germanium optical window by mask vacuum lithography and electron beam evaporation coating technology, and then the infrared dual-band anti-reflection coating and DLC protective film were coated by electron beam evaporation and PECVD on the germanium window, respectively. Furthermore, the transmittance in the infrared band and electromagnetic shielding effectiveness in the microwave band of the window were characterized. The results show that the windows coated with random-structure metal meshs, anti-reflection coatings and DLC films have excellent electromagnetic shielding effectiveness in the frequency range of 1GHz~18GHz, and have high transmittance in the 3.5μm~4.5μm and 7.5μm~9.5μm bands.
Silver-based high-reflective mirrors are widely used in optical applications such as large-aperture astronomical telescopes and spaced-based optics. The long-term stability of silver-based mirrors is of great importance to these applications. The development of more durable silver-based mirrors has been a hot topic in the optical coating community. In this paper, corrosion mechanisms of the protected-silver mirrors with a Sub/NiCrNx/Ag/NiCrNx/SiNx/Air structure were investigated in details. The corrosion features of a single layer Ag sample, which exposed to atmospheric environment for a few days, are observed by a Zeta-500 3D optical microscope. The durability of protected-silver mirrors with a structure of Sub/NiCrNx/Ag/NiCrNx/SiNx/Air is evaluated by accelerated environmental tests, including 360-hour salt fog test and humidity test. A transmittance measurement setup at the wavelength of 632.8 nm and a Perkin-Elmer Lambda 1050 spectrophotometer are used to monitor the transmittance and reflectance evolutions during the accelerated environmental tests. A Zeta-500 3D optical microscope is employed to analyze the corrosion features of the protected-silver mirrors after 360-hour accelerated environmental tests. X-ray diffractometer (XRD) is employed to analyze the microstructure before and after 360-hour accelerated environmental tests. Based on the experimental results, the potential corrosion mechanisms of the protected-silver mirrors were discussed in-depth. Furthermore, it was demonstrated that the transmittance evolution, which represents the pinhole density and therefore the degree of corrosion of the protected-silver mirrors, is valuable to evaluate the durability of silver-based mirrors.
Gemini-style protected-silver mirror (Sub / NiCrNx / Ag / NiCrNx / SiNx / Air) is a suitable choice for optical instruments requiring both long-term environmental durability and high broadband reflectance. Three Gemini-style protected-silver mirrors with NiCrNx interlayer thicknesses between 0.1 and 0.6 nm were prepared by magnetron sputtering, and the dependences of spectral properties and environmental durability of these protected-silver mirrors on the thickness of NiCrNx interlayer between the silver layer and SiNx layer were investigated in-depth. The reflectance, transmittance and total scattering loss measurements, optical microscope, and scanning electron microscope imaging were employed to characterize the spectral properties and surface morphology, and accelerated environmental tests, including humidity test and salt fog test, were applied to investigate the environmental durability. The experimental results showed that both optical and corrosion-resistant properties of protected-silver mirrors were NiCrNx interlayer thickness dependent, and an optimum NiCrNx interlayer thickness should be ∼0.3 nm for Gemini-style protected-silver mirrors to have reasonably both high reflectance in a broadband spectral range from visible to far infrared and good corrosion resistance for long-lifetime applications in harsh environments.
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