Research On White Light Interference Technology For Measuring The Refractive Index And Thickness Distribution Of The Capsule

The refractive index,thickness and its distribution parameters of cupsule are very important parameters in the physics experiment of laser inertial confinement fusion(ICF).It is very critical to measure accurately these parameters for the research of ICF physics experiment.Due to the small size of the capsule with a diameter of sub-millimeter,special spherical structure and high requirements for measurement accuracy,how to determine the the refractive index and its thickness distribution of the capsule is still an important research content in the field of target parameter measurement technology.In this paper,the measurement technology applied to deterimne the refractive index and thickness distribution of the capsule,which is based on the white light interference technology is studied.The corresponding results are as follows:(1)The theoretical analysis of white light interference is carried out.On this basis,the basic principles of white light vertical scanning interference technology and white light reflection spectrum technology are introduced detailedly.The experimental device for measuring the refractive index and thickness distribution of the capsule are developed.The experimental device is mainly composed of white light reflection spectrum detection module,target adsorption transposition module,three-dimensional motion module,air floating isolation platform.These functions,such as the negative pressure adsorption,the precise adjustment and the 360° rotation of the capsuleand are relized.(2)Based on the basic principles of white light vertical scanning interference and white light reflection spectrum,a method for measuring the refractive index of the capsule is proposed.The white light reflection spectrum is used to measure the optical thickness of the tcapsule,and the white light vertical scanning interference technology is applied to deterimne the optical path increment of light passing through the capsule.The refractive index and thickness of the capsule can be obtained by combining the two methods.The experiments for measuring the refractive index of capsule are carried out,and the influence of optical fiber diameter,integration time and other factors on the measurement results is analyzed.The data processing method applied to determine the wavelength of interference extremum by MATLAB curve fitting and determining the interference order by using the continuity of interference order is proposed.The experimental results show that the proposed method can measure accurately the refractive index of capsule and the measurement error is less than 1 %。(3)Based on the principle of white light reflection spectrum and the improved peak detection algorithm,the measurement experiment for measuring the GDP capsule thickness distribution is carried out,and the circular thickness distribution data of the capsule is obtained.The experiment results verify that the thickness measurement deviation is about0.1 μm.