Precise measurement of refractive index in the ambient environment using continuous-wave terahertz frequency-domain spectroscopy (THz-FDS)

In this paper, we present the application of THz frequency-domain spectroscopy (THz-FDS) for determining the refractive index in an ambient environment. The signal phase is extracted from the periodically oscillated photocurrent by a magnitude normalization method. The proposed method is demonstrated using experimental data of polytetrafluoroethylene and α-lactose monohydrate as reference materials collected at a relative humidity of around 17.0% ± 2.0%. A detailed comparison to the existing algorithms, including the Hilbert transform and extreme points analysis, reveals the remarkable reliability of our proposed method. This study expands the characterization capabilities of THz-FDS and furthers the development of practical terahertz spectroscopy applications.