Theory And System Research For Ultra-Thin Metallic Foil Thickness Measurement Based On White Light Interference

The mechanical fine process and the detecting technique are the advanced manufacture technology developed by national medium and long-term science and technology development and the Eleventh five-plan outline. An important application situation of precise metallic foils rolling thickness in 1 μm~100μm is preparation of Inertial Confinement Fusion (ICF) target materials. As the high added value product, metallic foils are also used in many industrial processes. Based on the national "863" program, research on Ultra-thin metallic foils thickness measurement technique is done in this dissertation. In correlative basic researches of Laser Fusion, such as in state equations researches under high-temperature and pressure, the strict requirements for high consistency thickness and surface quality of the micron dimension metallic foils are presented. The contact thickness meters used presently can damage samples and induce additional errors, which reduce the measuring precision greatly. Non-contact and high-precision thickness measuring system testing the micron dimension metallic foils can not found at oversea and domestic markets. Therefore, it is important especially to research accurate, non-contact, safe and fast thickness measuring techniques and corresponding measuring equipments, which has important significance.In the view of theoretical research and practical application, the principle and characteristics of white light spectral-domain interference are studied thoroughly in this dissertation;the interference spectrum analyzing methods of the ultra-thin metallic foil thickness measurement are studied thoroughly in this dissertation, mainly researching the tandem and two-path differential white light interferometry system, which composed of two white light Michelson interferometers, The reference signals including thickness information are received by USB2000 fiber optic spectrometer. Four aspects including the measurement principle, design scheme, data processing and experimental verifying are discussed particularly;According to testing principle, using the differential light path, reflective surfaces measured of two Michelson interferometers are the corresponding surfaces of metallic foil, so the final output interference spectrum of this system is only dependent on its thickness and is immune to its position. Therefore, the ability of anti-vibration of system will be improved. At the same time, utilization of white light spectral-domain interferometry could increase measurement range and anti-interference ability. The basic data processing techniques of tandem and two-path differential white light interfering spectrum were also included in the dissertation. According to requirement of specific testing environment, the data processing methods based on the wavelet transformation were presented toprocess tandem differential interference spectrum, and the data processing methods based on LRMS and the dynamic linear smooth and conic fitting to process two-path differential interference spectrum. As eliminating noises and smoothing curves, locating accuracy of the extreme points was increased. The technique based on the dynamic linear smooth and conic fitting is simple, fast, precision. Data controlling and analyzing software of this testing system were compiled according to this method.The thickness meter prototype based on two-path differential interference thickness measurement is made initially. The components, system calibration, testing results, performance index and influencing factors are discussed detailedly. In this prototype, The testing system has high optical resolution, the testing range is 1 jum-SOjum approximately, the testing stability is less than ±10?m in static measurement, it costs less than 50 ms within the single measurement, and transverse resolution is related to core diameter of transmitting light optical fiber and other factors, is approximate to 0.3 ///?. The measurement precision is 0.2% as metallic foil thickness is less than 20jum and 0.9% as metallic foil thickness is less than 40/j.m .The thickness meter not only has the characteristics of compact structure, but also has all merits of interferometry, such as non-contact, non-destructive, fast, high precision and high sensitivity, safety and credibility.There are some originality innovations in the dissertation. First, the interference spectrum analyzing methods of the ultra-thin metallic foil thickness measurement are presented, using the characteristic of spectral interference as OPD over coherent length, the dynamic range is advanced. Second, the data processing methods based on Wavelet transform, LRMS and the dynamic linear smooth and conic fitting to process differential interference spectrum resolved the key problems influencing system accuracy theoretically and technically, so the system can achieve very high precision. Last, The tandem differential WLI system used to measure Ultra-thin metallic foil thickness have not covered in any literatures and reports, which pioneers the new thought about using white light interference spectrum analyzing method to measure impending and opaque Ultra-thin foils and strips. The thickness meter prototype based on two-path differential interference thickness measurement is successfully developed for the first time in China, which realizes the index requirements put forward by Research Center of Laser Fusion, CAEP.