Tunable focusing in natural hyperbolic magnetic media

While optical effects such as negative refraction and imaging obtained from slab lenses with plane parallel sides are widely studied using metamaterials, it is less well known that these effects can occur naturally in certain materials. We discuss a class of natural hyperbolic materials that not only display similar effects but also allow one to modify the focal length of a slab lens with an externally applied magnetic field. This is possible because antiferromagnets are gyrotropic and support magnetic polaritons whose frequencies are sensitive to magnetic fields. In addition, a rich caustic structure emerges at low temperatures, when damping should be small. These materials also produce slab focusing at higher temperatures, although the caustic structure disappears

Oriented asymmetric wave propagation and refraction bending in hyperbolic media

Crystal quartz is a well-known anisotropic medium with optically active phonons in the THz region where hyperbolic phonon-polaritons can be excited. Here, we use this material to illustrate how the behavior of bulk and surface hyperbolic polaritons can be drastically modified by changing the orientation of the crystal’s anisotropy axis with respect to its surface. We demonstrate, both theoretically and experimentally, phenomena associated with the orientation of hyperbolic media. We show the consequences of changes in the crystal’s orientation in various ways, such as the modification of the effective reststrahl regions and associated surface phonon polariton dispersion. Of particular significance, however, is the transmission behavior of radiation passing through a rotated hyperbolic crystal. Here, even a small rotation of the optical axes with respect to the crystal surface can lead to a very large degree of asymmetry in the transmitted intensity. In addition, the refracting angle (which in a hyperbolic medium may correspond to negative refraction and slab lensing behavior) itself becomes asymmetric, so that a slab lens with a laterally displaced image becomes possible. We discuss some of the possible consequences of these types of effects

Anomalous wave propagation in quasiisotropic media

Based on boundary conditions and dispersion relations, the anomalous propagation of waves incident from regular isotropic media into quasiisotropic media is investigated. It is found that the anomalous negative refraction, anomalous total reflection and oblique total transmission can occur in the interface associated with quasiisotropic media. The Brewster angles of E- and H-polarized waves in quasiisotropic media are also discussed. It is shown that the propagation properties of waves in quasiisotropic media are significantly different from those in isotropic and anisotropic media.Comment: 15 pages, 4 figure

Characterisation of molecular weight and compositional heterogeneity in block copolymers

A gel permeation chromatography (GPC) system, using two concentration detectors and a low angle laser light scattering (LALLS) detector, has been investigated for use in characterising copolymers. At each elution volume, the system allows the calculation of molecular weight, average composition, and compositional heterogeneity. Overall molecular weight, composition, and heterogeneity parameters can also be calculated. This characterisation method yields heterogeneity information previously unobtainable without the use of cross fractionation techniques which are far more time consuming but ultimately more thorough. [Continues.

Beam Shifts of Far-Infrared Radiation on Reflection off the Anisotropic Crystal LiYF₄

We investigate the Goos-Hänchen shifts associated with phonons in the anisotropic crystal LiYF<sub>4</sub>. In p-polarization the shifts can be either positive or negative, and various mechanism are discussed

Tunable All-Angle Negative Refraction in Antiferromagnets

We consider how the magnon response of an antiferromagnet may be used to induce negative refraction at terahertz frequencies and how the angle of refraction may be tuned using an external magnetic field

All-Angle Negative Refraction from the Phonon Response in Anisotropic Crystals

We consider how all-angle negative refraction may be induced in anisotropic crystals by making use of the phonon response. We investigate, both theoretically and experimentally, the example of crystal quartz at far infrared wavelengths