Far-infrared and terahertz spectroscopic study on ancient Chinese papers

In this study we discuss the transmittance, the refractive index of seven ancient paper sheets and five modern paper sheets made in ancient technology in the interval 5-85cm-1 and 300-1000cm-1, with terahertz time-domain spectroscopy in transmission mode and Fourier-transform infrared spectroscopy in transmission mode. By analyzing the optical characteristics of these twelve paper sheets, we discuss the link between the ancient and modern paper.