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.
The report summarizes the design technique of middle infrared continuous zoom optical system with 2×expander and recites the design technique of optimizing continuous zoom optical system with expander, of correcting aberration in long focal length and large aperture optical system and of analyzing and controlling of narcissus effect. The above-mentioned techniques have formed a general method of designing continuous zoom infrared optical system with expander. Based on these design techniques, a MWIR long focal length continuous zoom optical system with expander has been developed. The system is composed of a 2× expander, a zoom system and a secondary imaging system with off-centred folded path which comprises eight lenses and two reflectors. The spectral band of the system is 3.7~4.8μm and it can realize 62.5mm ~ 500mm continuous zoom. This optical system can achieve 100% cold stop efficiency. The optical system can achieve 100% cold stop efficiency, smooth zoom and long focal length, and has large aperture and high image quality. The testing results show that its image quality can meet the requirements of application.
For cooled detector with staring focal plane array, a long focal length large aperture middle infrared continuous zoom optical system was presented. The zoom system is composed of eight lenses and two reflectors. The parameters and schematics of the system are given by using zoom system principle and optical design software. The image quality and narcissus of the system are analyzed. The system with 3.7~4.8μm spectial region can realize 88~1100mm range continuous zoom and fulfill 100% cold shield efficiency. The system has the advantages of long focal length, large aperture, high image quality and smooth zoom locus.
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