The phonon-polariton resonance of polar salts allows devising new structures that can confine far infrared/terahertz radiation in subwavelength regions. That would lead to a range of applications such as near-field microscopy or imaging. Polaritonic photonic crystals, based on phononpolariton resonances, have been theoretically studied and negative effective permeability has been predicted under conditions of large dielectric constant and low loss of the phonon-polariton building blocks. However, the physical realization of these structures implies generally lithographic techniques or micromachining. These are top-down approaches that, for large surfaces, use to be costly and time consuming. Directional solidification of eutectics, a self-assembling bottom-up alternative, can be used for the fabrication of large scale bi-material composites. These materials have anisotropic microstructure (and properties), large homogeneity in size scales of the microstructural features and high quality of the interphases. All these are desirable qualities for polaritonic composites. The study as polaritonic metamaterials of some highly ordered rod-eutectics (NaCl-LiF and KCl-LiF) has been already started with promising perspectives. In the present communication these and other systems which are experimentally realizable using directional solidification of eutectics are presented. Their composition, microstructure and dielectric response in the THz range are studied and discussed as potential polaritonic metamaterials. The phonon polariton resonances of alkali-halide salts take place at energies around 5 to 10 THz (wavelengths from 60 to 30 μm). At wavelengths comparable to the size of the microstructural features, Mie resonances due to the building blocks (e.g. fibers) have to be taken into account for the propagation of the electromagnetic waves in the system. At very large wavelengths compared to the size of the microstructure, the description of the bulk eutectic systems can be done with appropriate effective medium theories. Still in this case, subwavelength guiding along the salt1-salt2 interfaces takes place.

Resumen del trabajo presentado al 4th International Directionally Solidified Eutectic Ceramics Workshop celebrado en Washington (US) del 14 al 17 de octubre de 2012.

We acknowledge the CE for finantial support under grant NMP4-SL-2008-213669 (ENSEMBLE).

Peer reviewed