Time-Domain Terahertz Reflection Holograhic Tomography Nondestructive Evaluation System

We propose to demonstrate key elements of feasibility for a single-sided time-domain terahertz reflection holographic tomographic imaging (TD-THz RHT) nondestructive evaluation (NDE) system which will provide high quality three dimensional images of the interior of complex aerospace composite structures. 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 principal imaging technique has utilized 2D raster scanning of a THz transmitter and receiver to generate a two-dimensional image from the reflected signal intensity. The proposed STTR will use existing Picometrix THz imaging hardware, but incorporate measurements of the scattered THz fields, enabling full 3D reflection-mode reconstruction of non-metallic materials on a metallic substrate. It will use holographic information consisting of phase and amplitude data collected through a 2D sampling plane. The specific reconstruction algorithm to be developed is a novel model-based reconstruction algorithm. This will algorithm will maximize the 3D reconstruction accuracy for the data available. Various options for image angles and sample geometries will be explored. The final imaging system will incorporate 2D or 3D scanning hardware and multiple angle data collection to maximize 3D image quality in rapid scanning applications.