Microprobe-based Terahertz Near-field Imaging of Highly Scattering Pharmaceutical Coatings on Small Tablets

Pharmaceutical solid dosage forms can be inspected using terahertz time-domain spectroscopy systems. However, in many cases, the size, shape, and composition pose considerable challenges using classic far-field configurations. We demonstrate how these challenges can be overcome using microprobe-based THz near-field imaging in reflection-mode and a wavelet-based signal analysis algorithm. This technique reveals buried interface structures that were not resolvable before.