Abstract
We give a detailed analysis of a general realization of reflection terahertz time-domain spectroscopy. The method is self-referenced and applicable at all incidence angles and for all polarizations of the incident terahertz radiation. Hence it is a general method for the determination of the dielectric properties of especially liquids in environments where transmission measurements are difficult. We investigate the dielectric properties in the 0.1-1.0 THz frequency range of liquids using reflection terahertz time-domain spectroscopy. We apply the technique for the determination of alcohol and sugar concentration of commercial alcoholic beverages and liquors. The special geometry of the experiment allows measurement on sparkling beverages.
Highlights
Terahertz time-domain spectroscopy (THz-TDS) is a method for the determination of the real and imaginary part of the dielectric function, or the absorption coefficient and index of refraction
Since THz-TDS is a phasesensitive technique a determination of the complex reflection coefficient of a sample by reflection spectroscopy yields the equivalent information about the dielectric function of the sample
Reflection THz-TDS has earlier been used for investigations of the temperature dependence of the dielectric properties of water [1, 2], and recently Hirori et al used attenuated total internal reflection THz-TDS to study the optical properties of semiconductor materials and liquid water [5]
Summary
Terahertz time-domain spectroscopy (THz-TDS) is a method for the determination of the real and imaginary part of the dielectric function, or the absorption coefficient and index of refraction. The dynamic range and noise limitations in transmission and reflection THz-TDS measurements were investigated by Jepsen and Fischer [7] Both transmission- and reflection spectroscopy requires a reference spectrum, recorded under known conditions, in order to extract quantitative information about the dielectric function of a sample. Inspired by that work we derive here expressions that can be used for the calculation of the dielectric function of a sample material in contact with a transparent window material such as silicon, without limitations to the incidence angle and polarization state of the incident THz field This analysis is crucial for the correct evaluation of quantitative spectroscopic results from THz reflection spectrometers. We will investigate the influence of higher concentrations of sugar in the solutions, and demonstrate that the method can be used for the simultaneous determination of both alcohol- and sugar concentration in a solution
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