Research of 3.7 μm and 4.8 μm double band-pass filter on the surface of Al₂O₃

The characteristics, preparation and testing methods of 3.7 m and 4.8 m double band-pass filter on the surface of alumina substrate were introduced in the background of infrared optical and thin film technology. Alumina(Al2O3) was used in medium wave infrared optical systems usually because of its wide light transmission area and good fastness and ease of use in optical systems. The two-band band-pass filter with excellent reliability and spectral characteristics were successfully developed by means of speed control and ion assisted process. The films were characterized by software optimization and double-coating of pass-filters. The analysis shows that the design structure and the optimization algorithm have a significant impact on the passband flatness, cut-off depth and transmittance of the film. Preparation process, in addition to the appropriate evaporation rate, the use of slow evaporation and weak ion energy assist was also very important key technology. The final spectral transmittance test averaged over 87% and passed environmental tests to meet the usage requirements.