Research On Key Technology Of Surface-defects Detection Of ICF Capsules Based On Null Interferometric Microscopy

Inertial Confinement Fusion(ICF)is one of the hottest frontier researches in the world today,and the capsules with diameters ranging from several hundred microns to several millimeters,which are filled with deuterium-tritium fuel are the core components of ICF.However,the isolated defects on the surface of the capsules are important factors leading to the failure of ICF ignition at present.To successfully achieve ICF ignition,it is necessary to strictly control the size and number of defects on the surface of the capsules.So,the surface defects must be detected by topography methods with nano-level detection accuracy.As a non-contact,large-field,and directly-imaging method,interferometric microscopy can achieve nanometerprecision wide-field measurement of microscopic features.However,when applied to the detection of micro-spherical samples,traditional interference microscopy cannot take into account both high-resolution imaging and wide-field interferometry.Aiming at the shortcomings of existing capsule detection methods and interferometric microscopy methods,this paper studies a microsphere null interferometric microscopy method and applies it to highprecision,high-efficiency,and full-surface flawless detection of capsule surface defects.The main contents are as below:First,the basic theory of microsphere detection by interference microscopy is studied.The generation and phase-shifting principle of self-collimating wavefronts in the microsphere interference microscopy system are analyzed,which provides a theoretical basis for the study of null interferometric microscopy and the realization of high-precision detection of surface defects of the capsule.The propagation process of the interference wavefront in the microscope system is analyzed by the scalar diffraction theory and the incoherent imaging model of the diffraction-limited system.The principle of the phase unwrapping algorithm is studied,and the influence of residues on the unwrapping process is analyzed.Secondly,Aiming at the requirements of high-resolution and high-precision detection of surface defects of ICF capsules,a micro-sphere null interferometric microscope with decoupling of interference and imaging optical paths is proposed.By modulating the axial position of the point light source,the imaging relationship of the surface of the capsule with different curvature radiuses and the self-collimation illumination conditions are ensured.At the same time,the spherical reference mirror is used to compensate for the optical path of the spherical test wavefront.Compared with the traditional interference microscopy technology,it can effectively expand the scope of the interference field while imaging the surface of the capsule with high resolution.Aiming at the multi-surface reflection problem of the ICF capsules,a low-coherence light source system based on optical path matching is studied,which avoids the generation of parasitic fringes and enables the selection of interference beams by controlling the coherence of the light source.The feasibility of the phase-shifting method based on the light source system is analyzed,and a dynamic phase-shifting method based on a polarization camera is proposed,which can avoid the influence of environmental vibration on the measurement results.Thirdly,a defect phase recovery method is studied to solve the problems of defocusing and steep defect phase recovery under the limited depth of field.Aiming at the problem of defect defocus caused by the limited depth-of-field of the large numerical aperture objective lens,a defocus phase reconstruction method based on numerical diffraction calculation is studied.The diffraction reconstruction distance is calculated and sampled by establishing a microsphere imaging model,to reconstruct the defects in the full field of view.At the same time,the numerical diffraction transmission method of the spherical test wave based on a virtual lens is studied,which avoids the problem of sampling rate change caused by direct diffraction transmission of a spherical wave.Aiming at the problem of phase undersampling for steep defects,a residues-calibrated least-squares phase unwrapping algorithm suitable for undersampling phase maps is proposed.By identifying and correcting residues points,the influence of noise and undersampling on the solution of the Poisson equation is avoided,and the residual phase error is iteratively compensated,thereby improving the unwrapping accuracy of the undersampling defect phase.The above methods are used to extract the phase of the surface defects of the ICF capsule within the full field of view,and the relative error of the defect height restoration is 0.6%,which verifies the effectiveness of the method.Finally,aiming at the problem of high-efficiency and no omission detection of full-surface defects of micro-spherical capsules,a full-surface defect detection method based on twodimensional rotary scanning and computer-aided adjustment is studied.By constraining the relative positions of sub-apertures between layers and within layers,a positional arrangement model with the smallest number of sub-apertures under the condition of full surface coverage is established,and to reduce the accumulation of errors in the scanning mechanism.Aiming at the three-dimensional displacement of the subaperture caused by the eccentricity error of the capsule,An automatic online correction method of eccentricity error based on wavefront aberration decomposition is proposed to ensure the accuracy of sub-aperture measurement and positioning.Based on the above research work,a full-surface defects detection system of the capsule is designed and built,which realizes the high-efficiency detection and evaluation of the full-surface defects of the capsule.The relative error of the repeated measurement of the defect height by the system is less than 1%,which verifies the reliability of the method and the system.