Three-dimensional wide-bandwidth quantum energy truncation terahertz coherence tomography

A novel quantum energy truncation terahertz coherence tomography (QET-THCT) has been found to feature profuse (resonant) photon loss when the energy level of the emitted THz signal matches the molecular vibration energy excitation quantum. The concept of quantum energy level correlation truncation is introduced, where the reflected THz radiation from a solid is recorded and the output is translated to a frame sequence, each as a two-dimensional depth-coded image with the result being the highest degree of THz response localization to-date. By performing molecular excitation energy spectral truncation correlation, subsurface depth information can be retrieved according to energy localization and used for constructing 3-D visualizations (tomograms) of THz quantum-energy-resolution-level molecular fingerprints in wide classes of materials. Based on the quantum level truncation concept, the new modality breaks through major problems inherent in 3-D continuous-wave (CW) THz radiation imaging and its limited diagnostic capabilities to-date: scarcity of kinetic-dynamic/spectroscopic specificity for characterizing the interrogated material refractive index and its molecular/chemical composition and QET-THCT elimination of the need for additional (angular) scanning, a long-standing challenge in real-time THz-CT where a third dimension (angular rotation of the sample) must be measured, thus dramatically enhancing imaging speed and efficiency. Selected case-study examples include impact-induced damage, imaging of uneven distributions of multi-layer coatings, and subsurface kiss-bond/disbond defect imaging. QET-THCT exhibits high spatial resolution 3-D imaging capability down to sub-millimeter level and 10-fold depth resolution (4mm) compared to the intrinsic resolution in state-of-the-art commercial systems such as the one used in this work (40 mm).