THz Dielectric Characterization of High Loss liquids using Total Internal Reflection Time Domain Spectroscopy

We introduce a technique to remotely determine the salt content of high concentration salt solutions using terahertz time domain spectroscopy.~~Terahertz is highly sensitive to water content, however the absorption strength is so high, characterization of aqueous solutions with transmission spectroscopy is not feasible with standard sources.~~Previously investigators have overcome this limitation using terahertz total internal reflection time domain spectroscopy to characterize alcohol and sugar content in solutions {\{}P. Uhd Jepsen et al, Optics Express, Vol 15 No22 (2007){\}}.~~However the optical system used mixed the incident polarization content at the interface, increasing the complexity of the analysis.~~Our method again uses total internal reflection at a silicon-aqueous sample interface, but the optics ensure the polarization of the THz beam remains the same throughout simplifying the analysis.~~We have applied the technique for measuring the dielectric constants of high concentration salt solutions such as KI and NaI in the range 0.2 to 1.5 THz.~~The dielectric strength of these solutions is modified with increasing salt concentration and can be significantly higher than pure water.~