Our recent paper in Laser & Photonics Reviews reports that strong dielectric anisotropy at terahertz (THz) frequencies splits the Mie magnetic dipole mode in monocrystalline titanium dioxide (TiO2) micro-spheres. The splitting is experimentally confirmed using near-field THz time-domain spectroscopy. The resonances correspond to orthogonal magnetic dipole modes with narrow linewidths of only tens of gigahertz. The anisotropy of TiO2 can be exploited in the emerging THz all-dielectric metamaterial technology.

Abstract: Monocrystalline titanium dioxide (TiO2) micro-spheres support two orthogonal magnetic dipole modes at terahertz (THz) frequencies due to strong dielectric anisotropy. For the first time, we experimentally detected the splitting of the first Mie mode in spheres of radii 10-20μm through near-field time-domain THz spectroscopy. By fitting the Fano lineshape model to the experimentally obtained spectra of the electric field detected by the sub-wavelength aperture probe, we found that the magnetic dipole resonances in TiO2 spheres have narrow linewidths of only tens of gigahertz. Anisotropic TiO2 micro-resonators can be used to enhance the interplay of magnetic and electric dipole resonances in the emerging THz all-dielectric metamaterial technology.

Early view at:
Irina Khromova et al, 'Splitting of magnetic dipole modes in anisotropic TiO2 micro-spheres', Laser & Photonics Reviews, June 2016 (DOI: 10.1002/lpor.201600084)

Surface-plasmon resonances directly visualised by near-field terahertz time-domain spectroscopy. Sub-wavelength resolution of up to 2um allowed us to map the fields excited in THz resontaors - carbon micro-fibres.

Abstract: We present the temporal evolution of the terahertz (THz) field leading to the excitation of plasmonic resonances in carbon microfibers. The field evolution is mapped in space and time for the 3/2 wavelength resonance using a subwavelength aperture THz near-field probe with an embedded THz photoconductive detector. The excitation of surface waves at the fiber tips leads to the formation of a standing wave along the fiber. Local THz time-domain spectroscopy at one of the standing wave crests shows a clear third-order resonance peak at 1.65 THz, well described by the Lorentz model. This application of the subwavelength aperture THz near-field microscopy for mode mapping and local spectroscopy demonstrates the potential of near-field methods for studies of subwavelength plasmonic THz resonators.
Oleg Mitrofanov, Irina Khromova, Thomas Siday, Robert J. Thompson, Andrey N. Ponomarev, Igal Brener, John L. Reno, 'Near-Field Spectroscopy and Imaging of Subwavelength Plasmonic Terahertz Resonators', IEEE Transactions on Terahertz Science and Technology, V.6, No. 3, pp. 382 - 388  (2016)
DOI: 10.1109/TTHZ.2016.2549367

Our paper 'Tunable beam steering enabled by graphene metamaterials' (B. Orazbayev, M. Beruete, and I. Khromova) climbing up the list of Top Downloads in Optics Express.