| The advantages of ultraviolet solar band detect systems are simple structure, low false alarm rate, high sensitivity and strong concealment compared with the conventional systems. It has received the widespread attention in the field of optical relevant. However, the requirements of system imaging quality and resolution of this detection technology are very strict,and the spectral constraints are also rigid. Thus, optical thin film has become a hot pot and key technology. The materials for ultraviolet band are limited. Most of the materials have spectral absorption in this band, and the deposition process are complex. The thickness of the film is thin, so the thickness errors control is hard, the requirement for experimental equipment control accuracy is very high. All of these factors will bring some difficulties on the design and preparation of the film, and this is the main reason for limiting the development of solar blind ultraviolet detection technology. This subject is supported by “Ultraviolet signal XXXX technology” of “the 12 th Five-Year Plan” to study of detection system optical thin film, the specific research contents are as follows.(1) The substrate and coating material properties are researched, Contraposing the problems of ultraviolet material selective small, easily absorbed, large internal stress and complex refractive index matching, through the experiment to filter the ultraviolet film material. According to the measured spectral curve, using the envelope method to simulated calculation to get the optical constants of thin film material in this band.(2) Aiming at technical requirements of the solar blind ultraviolet system, four kinds of optical thin film which are ultraviolet antireflection film, interference edge filter, induced transmission filter and Fabry-Perot(F-P) band-pass filter are designed. Based on the basic theory of optical thin film properties and under the condition of the laboratory equipment, using the film system design software of Macleod, TFC, by analysing a series of parameters, such as the film of layer thickness, layer number of iterations, sensitivity, matching admittance and so on. The influence of film thickness error is simulated and the optimal film system is selected.(3) Film deposition technology is researched. Small variations of the vacuum chamber process parameters will lead to errors in the thin film deposition, especially in the ultraviolet band. Through the study of the sensitivity of the film, the state of the deposition material and the parameters of evaporation process, the problems of ultraviolet thin film, deposition error are solved.Aiming at the problem of ultraviolet film material is easy to absorb the spectrum, the experimental samples with different process parameters(vacuum degree, temperature, evaporation rate and ion source assistive technology, etc) are tested. By optimizing the process parameters, problems of spectral absorption caused by craft are minimized.Cutting factors calculation method is adopted and the film thickness distribution data are used to produced the corresponding baffle. By studying of the ion source system parameters deeply, the microstructure of the films are analyzed during electron beam evaporation, and the reasons for the poor quality of the films are found out. Samples prepared using different parameters. The spectrum and the surface quality of the film are analyzed to optimize the process parameters of the ion source assisted deposition. Metal film thickness prepared in this subject is too thin, it will bring a lot of difficulties for film thickness control by electron beam evaporation. By controlling the electron gun evaporation rate and the evaporation time and assisted by film thickness control device, we precisely control of the thickness of the metal film, the stability and repeatability of the film thickness control are realized.(4) The error are analyzed by software simulation and inversion. Finally we find out the causes of error, so as to further optimize the process parameters and get the ideal spectral curve. The specific research contents are as follows.Cumulative thickness deviation of each layer will result in transmittance region ripple for interference edge filter. Because the experimental equipment is equipped with double probe, we need to reverse inversion analysis thickness error to find out the probe change layer position, thus improve the film thickness control precision and compress pass-band ripple.The induced transmission filter is composed of a dielectric film and metal film. Aiming at the problem of the temperature difference between the dielectric and metal film, by analyzing of experiments with different temperature, a more reasonable temperature control method for induced transmission filter are proposed. The Fabry-Perot(F-P) band-pass filter is made up of multi-cavity. For the band of ultraviolet, quartz crystal control method can be used only. Based on the research of the quartz crystal detection principle, the thickness deviation is analyzed and simulated, finally through changing the tool factor of each layer to improve the thickness control precision.This paper developed a wide-band optical thin film covering the ultraviolet, visible, near infrared(200nm~1200nm), and the characteristics of the film is low transmittance background and the cut-off range is wide in this band. Eventually two kinds of deep cut-off solar blind interference filters are developed. The filter is matched with solar blind photomultiplier detector, which the main transmittance of 240nm~280nm is about 86.64% and the transmittance of 290 nm to 360 nm is less than one thousandth, the cut-off depth is OD3. The filter matching the CCD detector is with peak transmittance is 17.96% at the 260 nm, half bandwidth is less than 20 nm, and cut-off depth of 290 nm to 1200 nm are greater than OD4.The filter through the environmental monitoring and meet the system requirements. |
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