2-Dimensional mapping of frequency response of a single THz split-ring resonator probed by high speed asynchronous optical sampling

We investigate asymmetric split ring resonators (SRR) for the THz frequency range. These SRRs exhibit sharp resonances and strong field localization, which is of potential interest e.g. for biosensing of minute amount of sample material. Our near-field measurements show the local response of the SRRs on a scale much smaller than the resonance wavelength of 320 mum. Fig. 1 depicts the spatially resolved frequency response of an SRR at 1 THz and 1.4 THz, respectively. At around 1 THz an increase in the amplitude is observed when the tip is above the gaps of the SRR, whereas at 1.4 THz the amplitude pattern is more complex and shows maxima for the tip being further away from the SRR. We compare these experimentally determined frequency distributions to numerical calculations and discuss the influence of coupling between adjacent SSRs.