Dielectric spectroscopy up to 370 GHz has been performed on supercooled glycerol for temperatures between 250 and 330 K. The high-frequency dielectric loss, ´00 , has been investigated by coherentsource submillimeter-wave spectroscopy. Special attention is given to the dielectric loss in the crossover regime from the structural relaxation to the far-infrared response. A minimum is observed in ´00 ͑n͒ which is compared to theoretical concepts that predict fast relaxational processes. [S0031-9007(96)

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a b s t r a c t a r t i c l e i n f oWe present the results of broadband dielectric spectroscopy on two glass formers with strong JohariGoldstein β-relaxations. In addition to the α-and β-relaxation dynamics, the extension of the spectra up to 1 THz also allows revealing information on the fast β-process in this class of materials. There is clear evidence for a fast process contributing in the region of the high-frequency loss minimum, which is analyzed in terms of the idealized mode-coupling theory.

a b s t r a c tWe present a thorough characterization of the glassy dynamics of three propylene glycols (mono-, di-and trimer) by broadband dielectric spectroscopy. By covering a frequency range of more than 15 decades, we have access to the entire variety of dynamic processes typical for glassy dynamics. These results add three more molecular glass formers to the sparse list of materials for which real broadband spectra, including the region of the fast b-process, are available. Some first analyses of the various observed dynamic processes are provided.

This review highlights recent and novel trends focused on metallic (plasmonic) and dielectric metasurfaces in photoconductive terahertz (THz) devices. We demonstrate the great potential of its applications in the field of THz science and technology, nevertheless indicating some limitations and technological issues. From the state-of-the-art, the metasurfaces are, by far, able to force out previous approaches like photonic crystals and are capable of significantly increasing the performance of contemporary photoconductive devices operating at THz frequencies.