@article {doi:10.1021/acs.nanolett.5b04416,
	title = {Real-Space Mapping of the Chiral Near-Field Distributions in Spiral Antennas and Planar Metasurfaces},
	journal = {Nano Letters},
	volume = {16},
	year = {2016},
	note = {PMID: 26666399},
	pages = {663-670},
	abstract = {Chiral antennas and metasurfaces can be designed to react differently to left- and right-handed circularly polarized light, which enables novel optical properties such as giant optical activity and negative refraction. Here, we demonstrate that the underlying chiral near-field distributions can be directly mapped with scattering-type scanning near-field optical microscopy employing circularly polarized illumination. We apply our technique to visualize, for the first time, the circular-polarization selective nanofocusing of infrared light in Archimedean spiral antennas, and explain this chiral optical effect by directional launching of traveling waves in analogy to antenna theory. Moreover, we near-field image single-layer rosette and asymmetric dipole{\textendash}monopole metasurfaces and find negligible and strong chiral optical near-field contrast, respectively. Our technique paves the way for near-field characterization of optical chirality in metal nanostructures, which will be essential for the future development of chiral antennas and metasurfaces and their applications.},
	doi = {10.1021/acs.nanolett.5b04416},
	url = {http://dx.doi.org/10.1021/acs.nanolett.5b04416},
	author = {M. Schnell and P. Sarriugarte and T. Neuman and A. B. Khanikaev and Shvets, G. and J. Aizpurua and R. Hillenbrand}
}
