Terahertz near-field imaging of electric and magnetic resonances in metamaterials

Experimental investigations of the microscopic electric and in particular the magnetic near-fields in metamaterials remain highly challenging and current studies rely mostly on numerical simulations to characterize their resonant microscopic behavior. Here, we present a terahertz imaging technique, which allows us to measure the amplitude, phase and polarization of the electric near-fields in the vicinity of the resonant structures in planar metamaterials. By our approach we are able to trace the electric field vectors close to the structures after their excitation on sub-ps time scales with sub-wavelength spatial resolution. From the measured in-plane electric vector fields we are able to reconstruct the out-of-plane magnetic field vectors. As a result we obtain a comprehensive microscopic picture of the electromagnetic response in metamaterials.