Mid Infrared Energy Regulation Filter

In order to reduce the interference of environmental factors in information collection and improve the detection accuracy, we propose to suppress the 3.5 similar to 4.2 mu m band of light and make the 4.4 similar to 5 mu m band of light high transmittance by thin film technology. A kind of 3.5 similar to 5 mu m mid-infrared energy regulation filter is developed. The filter can suppress the stray light in the background band and allow the target signal to pass through in a certain proportion with the background signal. The infrared imaging system with the filter can collect the energy of different bands at the same time in a certain angle range for comparison,and use the different target information energy ratio of different bands to solve the problem of environmental interference in information acquisition and improve the detection accuracy. According to the requirements of the imaging system, a mid-infrared energy regulation filter film was designed and fabricated on a Si substrate,and the working wavelength range was 3.5 similar to 5 mu m. For spectral requirements of the filter, the matching between the film material and the substrate, the transparency zone, the mechanical strength, the refractive index and the stress matching between the film material should be considered. Ge and SiO were selected as the high refractive index material and low refractive index material, which spectral transmittance data could be tested by Fourier infrared spectrometer. Then the spectral data measured were fitted to calculate the accurate optical constants. The evaluation function can effectively evaluate the advantages and defects of the film design. In this paper, the proportion requirement of the energy regulation filter is strict, and the existing evaluation function is difficult to design a film design with smooth spectral curve and balanced energy distribution. According to the basic theory of optical film, a new evaluation function was established to reduce the tolerance, balance the relationship between the number of layers and thickness of the film and the evaluation function, and the Macloed film system design software was used to design the film system. The mid-infrared energy regulation filter membrane prepared in the first stage could not pass the temperature and humidity test, which didn't meet the requirements for spectral drift caused by moisture absorption. To solve the problem, we analyzed the characteristics of thin film of moisture absorption by studying micro composition of energy adjusting filter membrane, and analyzing the principle of optical performance changes before and after the temperature humidity test. The refractive indexes of Ge and SiO were calculated by designing of thin film material's experiment after moisture absorption. In the second stage,the optical parameters of Ge and SiO before and after moisture absorption were comprehensively used to optimize the design of the filter system of mid-infrared energy regulation. The developed filter solved the problem of optical performance degradation in humid environment for a long time. The preparation method of the mid-infrared energy regulated filter film is physical vapor deposition. The specific process is ion beam sputtering of Ge and SiO film materials after the substrate temperature is heated to 150 degrees C by VEECO vacuum coating machine, and stepped annealing is carried out after plating. Finally, the developed mid-infrared energy regulation filter film is tested and analyzes by PE Fourier infrared spectrometer. The test results show that the energy regulation ratio of the developed energy regulation filter is 1:41.9 before absorption and 1:40.7 after absorption at 0 degrees incidence. When incident at 30 degrees, the energy regulation ratios before and after moisture absorption are 1:40.4 and 1:39.04, which meet the system requirements. The results of surface roughness test with Zygo Verifire interferometer show that the peak valley value and root mean square value are 0.564 and 0.138, which meet the application requirements. And the optical performance of the filter can maintain stable in humid environment.