Narrow Bandpass Filter Effect on Terahertz Pulsed Imaging

Terahertz Pulsed Imaging (TPI) is a non-destructive spectroscopic technique that leverages the properties of terahertz radiation to resolve the properties of thin (∼microns) or multilayered systems, with applications in manufacturing, pharmaceutical, and healthcare diagnostics. To do so, TPI requires a broad and continuous frequency spectrum to achieve high-resolution and quantitative accuracy. However, portions of this spectrum fall within frequency bands that are regulated or restricted by the International Telecommunication Union (ITU), potentially leading to a conflict. To comply with ITU regulations, future commercial TPI technologies could require spectral filtering, to notch out protected frequency bands. In this study, we investigate the effect of such notch filters on TPI applications. We show that notch filtering leads to a substantial decrease in the accuracy of thickness measurements, even in the simplest such measurement. The implications of this performance degradation should be considered in future regulatory discussions.