New p - Ge THz laser spectrometer for the study of solutions:THz absorption spectroscopy of water

We present the development of a high power, tunable far-infrared p -germanium laser spectrometer for the study of dissolved biomolecules in the THz range. As a first application we report on the measurement of the absorption coefficient α for liquid water in the frequency range from 81 to 96 cm − 1 . Using the p - Ge laser spectrometer we were able to penetrate through layers of up to 100 μ m thickness. We discuss the advantages and the limitations of this THz spectrometer. We present an analysis of the experimental data based on a χ 2 test to provide an objective procedure to minimize the influence of systematic effects, for example of interference due to multiple reflections within the sample chamber. The measured absorption coefficient α lies between ( 410 ± 6 ) and ( 490 ± 6 ) cm − 1 at 81 and 96 cm − 1 , respectively.