Research And Fabrication Of Infrared Dual-band Filter In Detection System Of Methane

The application of Infrared thermal imaging detection technology of gas in gas detection field is becoming more and more widely with the development of infrared detection technique.The passive infrared thermal imaging detection technology of gas which is becoming a new research hotspot is contactless,dynamic and visualized,and it has the advantage of simple structure and large detection field of view.The passive infrared thermal imaging detector of methane in existence can detect only an infrared characterized absorption peak of methane,and the sensitivity of detector would be promoted effectively by detecting two peaks simultaneously.An infrared dual-band filter whose substrate was monocrystalline germanium using Ge and ZnS as high and low refractive index materials was developed in this paper in order to meet the requirement of detector that detecting two infrared characteristic absorption peaks of methane simultaneously under the premise of cut-off background noise effectively.A splitting design scheme with high experimental feasibility was proposed by splitting cut-off waveband at 6.0 μm based on the design theory of optical thin-film systems.The ZnS films with good film stability whose refractive index(3 μm)is less than 2.20 were obtained by investigating the relationship between the refractive index of ZnS film and ion beam through experiments,and the cut-off band is widened and the spike on cut-off band is eliminated by use it in design,accordingly,the design of front layers was realized;The number of variables to analyze of aperiodic narrow-band filter was decreased by choosing the result of back layers design which had a small quantity of controllable thin films,by this way the physical thick of layers was reduced and the optimization effect was improved,in this case the experimental feasibility of back layers could be improved effectively.The minimum deposition temperature of layers which is benefit to obtaining the ZnS film with lower refractive index was obtained by investigating the relationship between the gather density of germanium film and deposition temperature of layers through experiments in the manufacture of layers.The evaporation process of cricoid ZnS thin-film material was proposed which could obtain a stable deposition rate of ZnS layers,and the Tooling of ZnS was stabilized and the pocks was eliminated accordingly.This process could improve the reliability of ZnS material effectively for the development of infrared filter,and it also could reduce the difficulty of manufacture of infrared filter and improve the appearance of the filter.The requirement of spectral parameters of filter could be met easily by means of two inverse analysis through controlling the thin layers with high layer sensitivity brought in layers purposely at the stage of optical thin-film system design.The transmissivity of prepared dual-band filter is 89.25% at 3.31 μm and 81.97% at 7.67 μm,and the average transmittance of cut-off bands 3.71~7.47 μm and 7.87~10 μm was 0.36% and 0.36% respectively through testing the spectrum of filter.The prepared filter passed the tests of environmental resistence and spectral stability,and it could realize the purpose that improving system sensitivity for the contrast of the detected image was effectively improved when it the prepared filter was used in methane detector.