High-sensitivity terahertz spectroscopy for enhanced resonance detection of microscopic and sub-milligram quantities of lactose powder

In this study, we investigate the terahertz (THz) characteristics of α-lactose monohydrate powder using a tapered parallel-plate waveguide (TPPWG) technique, which facilitates the analysis of microscopic and sub-milligram quantities. Our results show that the TPPWG method not only minimizes the required sample quantity but also enhances the THz wave interaction with the powder sample, which ensures strong resonance features even with minimal material. The TPPWG technique measured higher-quality resonances using only 0.94% of the lactose powder mass, compared to the traditional pellet measurement method. Despite using only 0.91 mg of lactose powder, the TPPWG technique detected a wide bandwidth and clear resonance peaks with a relatively small base absorption, up to 14 times smaller than the pellet measurement. In addition, it was confirmed that the absorbance characteristics remain consistent regardless of the geometric distribution of the lactose layer as long as the mass or volume of the lactose powder is the same. These findings highlight the TPPWG method's potential for efficient and reliable THz characterization of powdered samples.