One-Sided 3D Imaging of Non-Uniformities in Non-Metallic Space Flight Materials

In this Phase II project, we propose to develop, construct, and deliver to NASA a prototype single-sided computed tomography time-domain terahertz (single-sided CT TD-THz) scanner accessory. This accessory will be suitable to be mounted onto a non-destructive evaluation (NDE) imaging gantry for the single-sided inspection of spacecraft and launch vehicle composite structures. The single-sided CT TD-THz scanner will be an accessory which works with existing T-Ray 4000<SUP>REG</SUP> TD-THz NDE imaging instruments owned by NASA (and other aerospace firms). We will also develop, and deliver a software package which employs the model-based image reconstruction (MBIR) methods. The MBIR method allows the reconstruction of 2D slices in depth from the data acquired by the single-sided CT TD-THz scanner. These 2D slices can then be stacked laterally to generate 3D images of sub-surface structures, features and defects. Time-domain terahertz imaging in the 0.1 to 3 THz spectral range is currently being used to characterize defects in Space Shuttle insulation and related materials. The proposed project will largely be configured from standard Picometrix THz sub-components, but incorporate measurements of the scattered THz fields, enabling full 3D reflection-mode reconstruction of non-metallic materials where only one side is accessible.