Authors from Delft University of Technology and Boston University have utilized sub-wavelength periodic metallic structures, known as metamaterials, for such investigations at terahertz frequencies. The split ring resonator (SRR) metamaterial is bianisotropic and, for this particular geometry, an applied time varying electric field induces a time varying magnetic dipolar response. The authors have fashioned this metamaterial on magneto-optically active single crystal terbium gallium garnet (TGG) which exhibits Faraday rotation - i.e. the polarization of an incident electromagnetic wave is rotated proportionally with respect to the strength of an external co-propagating magnetic field. Thus by characterizing the degree of polarization rotation of an incident mid infrared beam on a SRR metamaterial, a direct measurement of the magnetic near field was demonstrated. A simulated magnetic field enhancement of 200 is expected owing to the sub-wavelength nature of the metamaterial elements used. The authors highlight that with recent advances in generation of high field strength THz pulses, near field magnetic field strengths of 60 Tesla may be obtained. The above demonstration indicates that metamaterial TGG structures may provide a means to construct dynamic Faraday isolators and for creating dynamic magneto-electric materials.
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