Discussion on evaluation of terahertz frequency low absorbers using THz-TDS spectroscopy

Difficulties exist in the evaluation of low absorbers by terahertz spectroscopy. In particular, there is a lack of substantial reports in the literature on quartz, which is expected to be a low-absorption optical material for high-power terahertz wave applications. For the refractive index, there are no detailed reports of birefringence at terahertz frequencies, and for the absorption coefficient, there is variation in past literature values. Therefore, in this study, experimental and analytical methods were investigated to discuss the optical parameters of quartz crystal in detail.