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We present an optical study that reveals the bulk dynamics of the stratification process in drying colloidal dispersions. Terahertz time-domain spectroscopy has been used to measure in situ solventborne and waterborne paint layers as a function of drying time. The dynamic behavior of the dry top layer and wet bottom layer thickness, as well as the bulk thickness, reflect the principal processes of the established drying mechanism. In addition, the results demonstrate stratification only when the drying process is in the evaporation controlled regime, whereas the coating is shown to remain a single layer for diffusion controlled drying.

We propose a novel terahertz material analysis approach that provides highly accurate material parameters and can be used for industrial quality control. The method treats the inspected material within its environment locally as a stratified system and describes the light-matter interaction of each layer in a realistic way. The approach is illustrated in the time-domain and frequency-domain for two potential fields of implementation of terahertz technology: quality control of (coated) paper sheets and car paint multilayers, both measured in humid air.

The terahertz (THz) excitations in the quantum spin-ladder system Sr14Cu24O41 have been determined along the c axis using THz time-domain, Raman, and infrared spectroscopy. Low-frequency infrared and Raman active modes are observed above and below the charge-ordering temperature T(co) is approximately equal to 200 K over a narrow interval approximately equal to 1-2 meV approximately equal to 8-16 cm(-1)). A new infrared mode at approximately equal to 1 meV develops below approximately equal to 100 K. The temperature dependence of these modes shows that they are coupled to the charge- and spin-density-wave correlations in this system. These low-energy features are conjectured to originate in the gapped sliding motion of the chain and ladder subsystems, which are both incommensurate and charged.

We present a magneto-optical study of the three-dimensional topological insulator, strained HgTe, using a technique which capitalizes on advantages of time-domain spectroscopy to amplify the signal from the surface states. This measurement delivers valuable and precise information regarding the surface-state dispersion within <1 meV of the Fermi level. The technique is highly suitable for the pursuit of the topological magnetoelectric effect and axion electrodynamics.

We show an example of a purely magnetic spin resonance in EuTiO(3) and the resulting new record high Faraday rotation of 590°/mm at 1.6 T for 1 cm wavelengths probed by a novel technique of magneto-optical gigahertz time-domain ellipsometry. From our transmission measurements of linear polarized light, we map out the complex index of refraction n=√ϵμ in the gigahertz to terahertz range. We observe a strong resonant absorption by magnetic dipole transitions involving the Zeeman split S=7/2 magnetic energy levels of the Eu(2+) ions, which causes a very large dichroism for circular polarized radiation., (© 2011 American Physical Society)

We report a comprehensive THz, infrared and optical study of Nb-doped SrTiO3 as well as dc conductivity and Hall effect measurements. Our THz spectra at 7 K show the presence of an unusually narrow (<2 meV) Drude peak. For all carrier concentrations the Drude spectral weight shows a factor of three mass enhancement relative to the effective mass in the local density approximation, whereas the spectral weight contained in the incoherent midinfrared response indicates that the mass enhancement is at least a factor two. We find no evidence of a particularly large electron-phonon coupling that would result in small polaron formation.