THz near-field Faraday imaging in hybrid metamaterials
Spotlight summary: The electronic and magnetic structure of materials can be studied through characterization of the interaction of electromagnetic waves and matter. Although the spatial resolution of such investigations is fundamentally limited by diffraction (λ0/2π), various near field scanning techniques have overcome this bound thus permitting study of the electrical response of materials at nanometer resolution, independent of wavelength. However, comparable near field magnetic field measurements are usually only indirect or largely limited to DC. Recently, direct characterization of the magnetic near field has been achieved with a spatial and temporal resolution of λ0/200 and 100ps, respectively.
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.
Technical Division: Light–Matter Interactions
ToC Category: Metamaterials
|OCIS Codes:||(160.3820) Materials : Magneto-optical materials|
|(160.3918) Materials : Metamaterials|
|(180.4243) Microscopy : Near-field microscopy|
|(110.6795) Imaging systems : Terahertz imaging|
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