Spatial Reconstruction Algorithm of DT Layer in Cryogenic Targets Using Optical Techniques

The measurements of the solid DT layer, in terms of thickness and roughness, in the LMJ geometry (i.e. in a hohlraum) are not trivial. The DT layer measurements will be done using a Matsukov-Cassegrain telescope placed 39 cm away from the target. This telescope will be used to acquire shadowgraphy images on equators, and interferometric measurements on pole areas using optical coherence tomography (OCT). Optical coherence tomography allows determining the DT layer thickness on a few points, in the polar regions of the target. By scanning around the poles, several points can be acquired in order to calculate the roughness and the local shape of the DT layer at the pole. Both techniques were demonstrated on a 175 μm thick microshell with a 100 μm thick D 2 layer. A reconstruction algorithm was designed to give the whole shape of the DT layer from the partial data given by shadowgraphy and OCT. A 3D spatial estimation of the DT layer can be obtained. The algorithm efficiency was improved, with the use of 360 points on shadowgraphic image and 11 points on each pole. An estimation of the spatial DT layer shape was given on the first 90 longitudinal modes and on the first 5 equatorial modes.