| In recent years,optical precision measurement technology has been widely used in material analysis,biomedical testing,three-dimensional shape measurement and other fields.Refractive index,as an important optical parameter,is of great significance for performance characterization and has become an important research object.However,the traditional refractive index measurement methods have strict requirements on the size and shape of the sample,which can not meet the measurement of the refractive index of a small number of small objects.In addition,optical precision detection is also inseparable from the support of instruments and equipment.Therefore,a white light scanning interference system is designed and built in this paper.By adding a compensation plate on the system reference mirror,the limitation of short white light coherence length is overcome,the optical path is optimized,and the contrast between interference fringes is improved.With this system,the refractive index distribution of optical materials and Microorganisms can be measured accurately.The main research contents of this paper include:(1)The characteristics and principles of white light scanning interference are illustrated in this paper,and the spatial frequency domain algorithm,the seven-step phase shift algorithm and the Morlet wavelet transform algorithm are introduced in detail.And through simulation and experimental verification,it is concluded that the Morlet wavelet algorithm has the advantages of high-resolution accuracy,fast operation speed and strong anti-noise ability,which meets the requirements of the interference signal peak extraction of the system.(2)A set of white light scanning interference system is designed and built,and the linkage control of the hardware is realized.The ideal resolution of the system is obtained,and the flow chart of measuring refractive index of the white light scanning interference system is worked out.(3)After the interference light intensity of each pixel of the sample is obtained by using the white-light scanning interference system,the relative height between the optical material and the matching liquid with known refractive index is processed by using the Morlet wavelet transform method,then the refractive index distribution of the optical fiber and K9 glass can be obtained by calculating.The classical distribution function of optical fiber core is used as the evaluation function to fit the refractive index of the measured optical fiber core,and the fitting coefficient of determination of multi-mode fiber and single-mode fiber are 0.9972 and 0.9964,respectively.The error is 0.01% when comparing the experimental results with the official parameters.Two matching fluids with different refractive indexes are used to measure the refractive index of K9 glass,and the refractive index range of K9 glass is 1.5197-1.5210 and 1.5186-1.5198 respectively,which is basically consistent with the official data,indicating the accuracy of this method.(4)Combining optical detection with biomedical detection,the refractive index distribution of Caenorhabditis elegans is measured,which verified the feasibility of the system in biomedical detection.In conclusion,the white light scanning interference system designed in this thesis has the advantages of fast,high sensitivity,high precision and non-contact detection,which can be applied for the three-dimensional surface morphology of MEMS(Micro-ElectroMechanical System)、LCOS(Liquid Crystal on Silicon)and other devices packaged under the glass cover,the distribution of liquid refractive index in microfluidic channels,and refractive index of biological tissues and cells. |
