Contents I. Introduction
One of the most significant applications of terahertz time-domain spectroscopy (THz-TDS) is in studying and identifying biochemical and pharmaceutical materials [1], [2], [3]. Such materials are typically produced in the form of powders and must be compressed into pellets to enable quantitative spectroscopic measurements. They often have multiple strong polymorphic form-specific absorption features, such that pellets of practical thickness exceed the dynamic range (DR) of THz-TDS instruments at frequencies above 2 THz [4]. Consequently, in order to study the vibrational spectra of these materials over extended frequency bands, they are often mixed with a THz-transparent dilutant powder, such as polyethylene or polytetrafluoroethylene (PTFE) [1]. Studying spectra of organic materials in mixed-powder compressed pellets using THz-TDS is a widely employed and well-established technique. In using this method, it is assumed that the measured THz spectra of target materials are not altered by the sample preparation process, which includes factors, such as material concentrations, mixing, and compaction.
