Wavelet Shrinkage for Enhanced Chemical Recognition in the Rough Surface Diffused Terahertz Spectra

The rough surface scattering in the reflection-mode THz-TDS can result in inaccurate phase spectra, reduced signal to noise ratios, distorted or obscured resonant fingerprints, and the appearance of anomalous spectral artifacts. In this work, we demonstrate the implementation of a wavelet shrinkage technique for the retrieval of obscured resonant frequencies from the derivative of THz reflectivity of solid dielectric materials. We examine the robustness of this technique over controlled levels of rough surface scattering created using sandpapers of different grits on sample disks made from 4-aminobenzoic acid (PABA).