Development Of Wide Spectrum Filter For All-time Detector

With the increasing demand of market development,all-time detectors are widely used in daily life.As its name implies,all-time detector can realize all-time imaging in day and night,which plays an important role in daily life and national defense and military affairs.In order to achieve the purpose of all-time detection and imaging,the existing imaging systems mostly adopt the form of visible and infrared wavelength splitting to realize the separate imaging of two channels of light.The visible light system used for daytime imaging works separately from the infrared system used for night imaging.It can only work in a single band and cannot include the full band of ultra wide spectrum.After the target is imaged separately by the imaging system,the visible imaging and infrared imaging are combined through the image processing function of the computer,so as to achieve the purpose of all-time imaging.However,this method has the defects of relatively large volume,high power consumption and heavy weight of the imaging system,and the application range of the imaging system also has great limitations.In order to make the imaging system free from the limitation of measurement conditions and measurement range,it is very important to design a small,low power consumption and economical all time detector window filter.In this paper,systematic theoretical and experimental research work has been carried out in three aspects:the acquisition of optical constants of infrared thin film materials,the design and optimization analysis of filters,and the preparation and testing of filters.The main work and results are as follows:Based on the functional requirements of the all-time detector,this paper gives the functional requirements and refined indexes parameters of the wide spectrum filter,and refines the functional index parameters of the filter through the functional requirements of the all time detector.The specific indexes of four different filters:blue and Infrared(B+IR),green and Infrared(G+IR),red and Infrared(R+IR)and infrared(IR)were proposed.Multispectral zinc sulfide is selected as the substrate,and ytterbium fluoride(Yb F₃)and zinc sulfide(Zn S)are selected as the low refractive index and high refractive index materials for the film system design.(2)According to the index requirements of the filters,the substrates and film materials of the above four filters were selected,and the optical constants at different temperatures were given.The optical constants(refractive index n,extinction coefficient k)of the films in the ultra-broadband spectral range of 0.4?m?14?m were obtained by the combination of the envelope method and dispersion model fitting of the transmission spectral curves of the films.The accuracy of the optical constants obtained by the combination of the envelope method and the dispersion model fitting method was fully demonstrated by verifying the transmittance spectral curves in the spectral range from 0.4?m to 1.6?m by ellipsometry and by calculation with the TFCalc film system design software.And the optical constants of zinc sulfide were obtained by photometric method.It provides the basic conditions for the subsequent membrane system design.(3)On single-plane multispectral zinc sulfide substrate,four filters with different requirements was optimized and analyzed based on the design theory of interference cutoff filters by using TFCalc membrane system design software and optical constants obtained from experiments.The sensitive layer is obtained by sensitive layer analysis,and the relative tolerance range is calculated by relative tolerance analysis.A wide spectrum filter was prepared by electron beam thermal evaporation technology on a single multispectral zinc sulfide substrate by different processes.The transmission spectrum curves of visible band and infrared band were tested by spectrophotometer and Fourier infrared spectrometer respectively.The above four filters can meet the design requirements.