Terahertz Time-Domain Spectroscopy of Solid Samples: Principles, Applications, and Challenges

Advances in ultrafast lasers and semiconductor technologies have facilitated access to the terahertz (THz) frequency range for spectroscopic and imaging purposes. THz time-domain spectroscopy (TDS) is commonly used to acquire spectral data having high signal-to-noise ratios (SNRs) over a broad range of THz frequencies. THz-TDS instrumentation is commercially available, thereby enabling novel applications of THz time-domain (TD) imaging and spectroscopy in a myriad of applications. This review gives a general description of the instrumentation available for collecting THz-TD data and focuses on measurements of solid samples. Measurement geometries useful for collecting THz-TD data from solid samples are reviewed and a summary is presented of the major applications to the analysis of solid samples related to security issues, as well as samples originating from the pharmaceutical industry, dental sciences, biological samples, and polymer materials. Emphasis is also given to analytical applications in a discussion of the analytical challenges met in quantification of solid analytes by THz-TDS methods.