Second-harmonic optical spectroscopy on split-ring-resonator arrays.

Previous second-harmonic-generation experiments on metallic split-ring-resonator arrays have been performed at fixed fundamental laser center frequency. Here, we perform nonlinear optical spectroscopy on a first set of samples, revealing pronounced resonances. Furthermore, to clarify the role of higher-order split-ring resonances, we perform additional experiments on a second set of samples in which the fundamental split-ring-resonator resonance frequencies are lithographically tuned, whereas the higher-order resonances are fixed.

Spectral imaging of individual split-ring resonators.

We report on spectral imaging within individual silver split-ring resonators (SRRs) operating in the near infrared-visible range. We classified the optical eigenmodes from the measurement of their energies and nanometer scale spatial distributions. They are plasmonic standing waves that show great similarities with that of nanoantennas.

Electromagnetic interaction of split-ring resonators: The role of separation and relative orientation.

Extinction cross-section spectra of split-ring-resonator dimers have been measured at near-infrared frequencies with a sensitive spatial modulation technique. The resonance frequency of the dimer's coupled mode as well as its extinction cross-section and its quality factor depend on the relative orientation and separation of the two split-ring resonators. The findings can be interpreted in terms of electric and magnetic dipole-dipole interaction.

Second-harmonic generation from split-ring resonators on a GaAs substrate.

We study second-harmonic generation from gold split-ring resonators on a crystalline GaAs substrate. By systematically varying the relative orientation of the split-ring resonators with respect to the incident linear polarization of light and the GaAs crystallographic axes, we unambiguously identify a nonlinear contribution that originates specifically from the interplay of the local fields of the split-ring resonators and the bulk GaAs second-order nonlinear-susceptibility tensor. The experimental results are in good agreement with theoretical modeling.

Second-harmonic generation from complementary split-ring resonators.

We present experiments on second-harmonic generation from arrays of magnetic split-ring resonators and arrays of complementary split-ring resonators. In both cases, the fundamental resonance is excited by the incident femtosecond laser pulses under normal incidence, leading to comparably strong second-harmonic signals. These findings are discussed in terms of Babinet's principle and in terms of a recently developed microscopic classical theory that leads to good agreement regarding the relative and the absolute nonlinear signal strengths.