The NASA Constellation program has a need to non-destructively test (NDT) non-metallic materials (foams, Shuttle Tile, Avcoat, etc) for defects such as delaminations and voids. While imaging systems at terahertz frequencies (0.3 to 3 THz) have been demonstrated for 2D imaging of similar materials, they have not yet demonstrate full 3D volumetric imaging. To meet this need, LongWave Photonics proposes to use high-power, low-frequency terahertz quantum cascade lasers (QCLs) developed at MIT, to LongWave Photonics proposes a terahertz quantum-cascade laser based swept-source optical coherence tomography (THz SS-OCT) system for single-sided, 3D, nondestructive evaluation (NDE) of non-conductive materials. The THz SS-OCT system uses a frequency tunable QCL array to generate an interferometric signal between a reference mirror, and a sample. An algorithm is used to transform this signal into depth information of the interfaces within the sample. Phase I demonstrated the feasibility of measuring the interfaces of a dielectric on metal sample. In Phase II, we propose to demonstrate a complete scanning system for 3D imaging by upgrading the optics and mechanics. Improvements in the power levels and frequency bandwidth of the QCL source are expected to greatly improve the depth resolution and signal to noise ratio of the system. The milliwatt power levels of the QCL are expected to result in fast scan speeds. Operation of the SS-OCT system is expected to be relatively simple as the QCL is an electrically pumped, solid state source of terahertz radiation, capable of operation in a compact, high reliability crycooler as demonstrated in Phase I.