Research On Range Extension Method Of Depth Measurement Based On Wavenumber Scanning Interferometry

Wavenumber Scanning Interferometry(WSI)is a non-invasive,high-sensitivity,high-precision and tomographic measurement method.By means of the wavenumber linear sweep of the source and the full-field interference characteristics,WSI can realize the measurement of the three-dimensional deformation field inside the measured sample without scanning the mechanical parts,which is widely used in medical diagnosis,bioimaging,and composite material inspection.However,in the measurement process,the depth deformation field of the sample is obtained by Fourier transform of the spectral interferogram.In order to reconstruct the spectral information of the signal after Fourier transform,the sampling process needs to satisfy the Nyquist sampling theorem,which makes the depth measurement range limited by the Nyquist sampling rate.In order to expand the depth measurement range of the WSI system,this thesis accurately measures the optical path difference and deformation field information of the measured object by demodulating the two sets of sub-sampling data,effectively increasing the depth measurement range of the system by 3 to 5 times.The specific solutions are as follows:1)Aiming at the problem of optical path difference deflection under sub-sampling,a dual-channel optical path difference estimation algorithm is proposed.By constructing the mathematical relationship between the ranges of the two sets of sub-sampling data,the true value of the optical path difference of the interference signal and the deflection value of the optical path difference,the true value of the optical path difference exceeding the range is estimated.In addition,in view of the "aliasing" phenomenon of the optical path difference that may occur after deflection,an optical path difference de-aliasing algorithm based on the MUSIC algorithm is proposed to improve the resolution of the optical path difference component in the spectrum,so as to reduce the "aliasing" of the optical path difference.2)Aiming at the problem of inaccurate deformation field extraction under sub-sampling,a deformation field estimation method based on Hilbert transform is proposed.Combined with the estimated optical path difference information,only a set of sub-sampling time-domain interference signals is needed to solve the wrapped phase difference of the interference signals before and after deformation.Then use the least square method to unpack the phase,and finally demodulate the deformation field distribution under the deformation of the interference signal.In addition,in order to reduce the influence of noise such as speckle and improve the quality of the measurement results,a noise reduction method based on fuzzy mathematics is designed to suppress the noise.3)An experimental measurement system is built,and the interference signal is resampled by monitoring the wavenumber in the interference signal,so that the time-domain interference signal meets the requirements of equal spacing sampling.A verification experiment and three application experiments are designed: topography profile measurement,tomographic profile measurement and tomographic deformation measurement.Through the analysis of experimental results,it is verified that the large range method in this thesis can effectively improve the measurement range of WSI.