Theoretical design and preparation of high performance MWiR notch filter

In order to effectively suppress the interference of CO₂ radiation 4.3 μm on MWiR target signal with wavelength of 3 μm−5 μm, based on the Needle random intercalation optimization algorithm, an accurate inversion correction model for the growth error of multi-layer ultra-thick Ge/Al₂O₃ films under quartz crystal monitoring is established by the electron beam evaporation method, thus realizing the design, the accurate inversion and the accurate preparation of MWiR notch filter. In order to solve the problem that the surface profile of the MWiR notch filter changes greatly, the preset substrate surface method is used to realize the low surface profile regulation of MWiR notch filter. The results show that the high refractive index Ge film has good deposition stability with the increase of coating time, while the deposition scale factor of low refractive index Al₂O₃ thin film changes up to 11.9% in a regular gradual trend. For the prepared MWiR notch filter, the average cut-off transmittance is less than 0.3% in the wavelength range of 4.2 μm−4.5 μm, and the average transmittances are more than 95% in the wavelength range of 3.5 μm−4.05 μm and 4.7 μm− 5.0 μm. The surface profile of the substrate after coating can be effectively controlled in a small range. The film has good adaptability to complex environment, and has successfully passed the environmental test of firmness, high temperature, low temperature and damp heat specified in GJB 2485-95.