Ellipsometry is a technique whereby the measurement of the two orthogonalpolarization components of light reflected at glancing incidence allows acharacterization of the optical properties of a material at a particularfrequency. Importantly, it obviates the need for measurement against a standardreference sample, and so can provide reliable spectroscopic information evenwhen surface morphology is unknown, of marginal quality and/or a reference isunavailable. Although a standard technique in the visible range, it has notbeen widely applied in the Terahertz (THz) spectral range despite its potentialutility. This is largely because of the technical difficulties that thesefrequencies present. This review details recent progress in the implementationof THz range ellipsometry. We discuss a variety of configurations includingvarious kinds of laboratory and facility based sources using both continuouswave and pulsed spectroscopic methods. We discuss the general problemsencountered when trying to import the methodologies of visible rangeellipsometry to the THz range and give examples of where the technique has beensuccessful thus far.
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