29 April 1999 THz spectroscopy of polar liquids
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The mesoscopic structure of water has long been a subject of discussion. We postulate that, on the mesoscopic scale, liquid water forms nm-size ice-like crystals and that his structure is responsible for absorption in the THz-frequency range. However, until the recent development of Thz-time domain spectroscopy (THz-TDS), it was difficult to determine the optical constants in this frequency range with a good signal-to-noise ratio and hence to study the absorption properties of water. Here we report on the optical properties of water in the frequency range 0.05-1.4 THz and discuss the mesoscopic structure of water. We use THz-TDS based on photoconductive dipole antennas gated by a 150 femtosecond laser pulses to generate and detect the THz- frequency pulses. A new theoretical approach is also presented which were use to explain the absorption behavior in the measured THz frequency range. In this theory, molecular plasma oscillations of H3O2 complexes, that are distinctly separate from the H5O2+ complexes which form an underlying crystalline lattice, are assumed to be responsible for absorption in the THz- frequency range. This model provides good agreement to our data.
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Imke. H. Libon, Imke. H. Libon, M. Hempel, M. Hempel, S. Seitz, S. Seitz, Nancy E. Hecker, Nancy E. Hecker, Jochen Feldmann, Jochen Feldmann, A. Hayd, A. Hayd, G. Zundel, G. Zundel, Daniel Mittleman, Daniel Mittleman, M. Koch, M. Koch, "THz spectroscopy of polar liquids", Proc. SPIE 3617, Terahertz Spectroscopy and Applications, (29 April 1999); doi: 10.1117/12.347127; https://doi.org/10.1117/12.347127

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