Terahertz Parametric Generators and Detectors for Nondestructive Testing Through High-Attenuation Packaging Materials

Here, we introduce an injection-seeded terahertz (THz)-wave parametric generator (is-TPG) spectroscopic system and its application to nondestructive inspection through a packaging material with high attenuation. Recent technological innovations have dramatically improved is-TPG output. Combined with THz parametric detection, whereby detection is performed in the reverse process of generation, a spectrometer with an extremely high dynamic range has been achieved. THz spectroscopic imaging has enabled the previously difficult visualization of substance spatial distributions, even through thick packaging materials. Moreover, the introduction of machine learning has improved the accuracy of identification. High-speed wavelength tuning and multi-wavelength generation enable real-time acquisition of sample information and real-time identification by image recognition, thus broadening the range of applicability of the is-TPG. Additionally, detection sensitivity has improved to a level of < 1 aJ through multi-stage THz parametric detection. The system combining is-TPG and THz parametric detection now exhibits a dynamic range of 125 dB, enabling imaging through thick, high scattering materials with an attenuation factor of −100 dB; to our knowledge, such measurements are difficult to achieve with other THz-wave systems.