Optimal ‘Tomography’ of 2-Layered Targets: 3D Parameters Reconstruction from Shadow Images

Interferometric microscope with a confocal focusing for inner surface defect detection of ICF capsule

Inner surface defects of inertial confinement fusion (ICF) capsule are a key factor leading to ignition failure; however, there are still no effective and non-destructive detection methods available. To solve this problem, we propose the first interferometric microscope with confocal focusing (CFIM). CFIM first uses confocal technology to achieve accurate axial positioning of both capsule and the camera, thereby ensuring that the inner surface of the capsule is precisely and clearly imaged at the camera. Then, phase-shifting interferometry based on a short-coherence source and a spherical reference is applied to obtain inner defects result from null inner surface interferograms. In addition, in-situ focusing is realized by the axial adjustment of camera, but not by the capsule, to ensure that the outer defects and the fake inner defects caused by it have the same pixel coordinates, thereby solving the confusion of fake inner defects. The comparative experimental results of the CFIM and the scanning electron microscope (destructive detection) prove the feasibility of the proposed method. With unique precision confocal focusing and in-situ focusing ability, CFIM provides the first approach for non-destructive detection of inner surface defects of ICF capsule to the best of our knowledge.

Detailed investigation of the iterative analysis for inertial confinement fusion target characterization

The iterative algorithm based on optical path difference and ray deflection (IAORD) is investigated in detail, and an advanced version (AIAORD) is proposed to obtain the refractive indices of the shell and the ice layer of the inertial confinement fusion (ICF) target simultaneously. The concept of the fixed-point iteration is introduced in the advanced algorithm, and it is found that the right choice of the combination of the input values and the characteristic curves is the key to ensure convergence in the iteration. The test uncertainties of the index measurement are analyzed by simulations, and they show that the uncertainties of the refractive indices of the shell and ice layer are 9.94% and 1.20%, respectively. Characteristic curves of typical ICF targets are studied, from which we conclude that AIAORD is versatile and suitable for the applications with any two unknown target parameters to be solved.

ICF target DT-layer refractive index and thickness from iterative analysis

An iterative algorithm based on optical path difference (OPD) and ray deflection is proposed to obtain the DT (deuterium-tritium)-layer refractive index and thickness of the ICF (inertial confinement fusion) target simultaneously. Starting from an assumed initial value, the refractive index and thickness are solved back and forth until the iteration stopping criterion is reached. Simulations show that the relative retrieval error of the DT-layer refractive index is better than 0.05% after finite iterations, and that of the thickness is better than 0.1%. Experiments show that the target shell refractive index and thickness can be retrieved with a relative error below ±2%. The test uncertainties from experiments were also analyzed.