Effects of Coherent versus Incoherent Illumination and Imaging Setup on Experimental Measurements of Scattering Amplitudes in Metamaterials
Sotiris Droulias, Costas M. Soukoulis, Thomas Koschny
Abstract
The characterization of metamaterials typically depends on the determination of scattering parameters like transmittance and reflectance, and comparison with numerical models. While, numerically, coherent plane wave scattering amplitudes for infinite perfectly periodic samples are readily accessible, experimental measurements necessarily involve scattering of possibly incoherent optical probes with finite-size illumination spots on finite sample surfaces that need to serve as a proxy for the true plane wave scattering amplitudes. In some situations, but not always, this difference can lead to substantially different observed scattering spectra. Here, we investigate and analyze the observable effects on the measured scattering spectra originating from coherent versus incoherent optical probes, finite illumination spot size, magnifying imaging systems, as well as beam shaping optical elements. We discuss the relation of all the above to the wave vector content of the illumination and the sample’s spatial dispersion properties, and we show that they can result in qualitatively significant deviations of observed scattering spectra from true plane wave scattering, which needs to be taken into account to really understand experiments and allow a faithful comparison with simulations.