We report that planar chiral structures affect the polarization state of light in a manner similar to three-dimensional chiral (optical active) media. In experiments with artificial metal-on-silicon chiral planar gratings of 442 wallpaper group symmetry, containing millions of chiral elements per square centimeter, we observed rotation of the polarization azimuth in excess of 30 of light diffracted from it. The rotation was found to change its sign for two enantiomeric forms of the media and to have components associated with both the structural arrangement and the chirality of individual structural elements. DOI: 10.1103/PhysRevLett.90.107404 PACS numbers: 78.67.-n, 78.20.Ek The ability of left-right asymmetrical (chiral) threedimensional molecules to rotate the polarization state of light known as optical activity is one of the most remarkable effects in optics that has been extensively studied since its discovery at the beginning of the 19th century. An optical active medium (for example, a medium consisting of randomly oriented helixlike molecules) will show opposite signs of polarization azimuth rotation for the two mirror-symmetric (enantiomeric) forms of the constituting molecule. The general concept of chirality also exists in two dimensions [1][2][3][4], where a planar object is said to be chiral if it cannot be brought into congruence with its mirror image unless it is lifted from the plane. One could therefore envisage a planar chiral medium that consists of ''flat'' chiral elements possessing no line of symmetry in the plane. So far, there have been only a few theoretical publications on the optical manifestations of such planar chirality. Hecht and Barron predicted incoherent circular differential Rayleigh and Raman light scattering from an ensemble of planar chiral molecules [5]. They showed that genuine strong chiral scattering phenomena could be generated through pure electric dipole interactions (in comparison with the much weaker processes involving magneto-dipole interaction in threedimensional chirality), while Arnaut and Davis calculated the scattered fields from the two-dimensional chiral structure of a metallic wire gammadion and found rotation of the polarization azimuth of the scattered field [6]. However, there have as yet been no reports of experimental observations of any optical manifestations of planar chirality, apart from the observation of a random chiral component in a highly localized near-field polarization effect in metallic fractal aggregates [7]. Consequently, it has yet to be shown whether planar chiral media could affect the far-field polarization state of light scattered on it in a manner similar to three-dimensional chiral media when the polarization effect is sensitive to the handedness of the structure. Here we report that we have manufactured left-and right-handed forms of a regular artificial medium consisting of microscopic chiral metallic objects distributed regularly in a plane, with a density of several millions per square centimeter. In this artificial medi...
We report unambiguous experimental evidence of broken time reversal symmetry for the interaction of light with an artificial non-magnetic material. Polarized colour images of planar chiral gold-on-silicon nanostructures consisting of arrays of gammadions show intriguing and unusual symmetry: structures, which are geometrically mirror images, loose their mirror symmetry in polarized light. The symmetry of images can only be described in terms of anti-symmetry (black-and-white symmetry) appropriate to a time-odd process. The effect results from a transverse chiral non-local electromagnetic response of the structure and has some striking resemblance with the expected features of light scattering on anyon matter. 73.20.Mf, 71.10.Pm Light-matter interactions involving non-magnetic materials are generally believed to obey time reversal symmetry, which is seen as a direct consequence of the timeinvariance, when taken separately, of non-magnetic media and the Maxwell equations. However, when the reversability argument is considered, the respective orientations of the electromagnetic wave propagation direction and the medium it interacts with may also be important, for instance in the case of planar chiral structures (PCS). A planar chiral structure is a pattern that cannot be brought into congruence with its mirror image unless it is lifted from the plane. In essence a planar chiral structure has a perceived sense of 'twist'. In 1994, Hecht and Barron, noted that the sign of the twist reverses if the structure is observed from different sides of the plane, and that this should also be the case for light polarization effects associated with the structure [1]. The possibility that this could imply the breaking of time reversal symmetry has been discussed in our recent papers [2,3]. Here, we report on experimental evidence of a time non-reversal interaction between light and an artificial non-magnetic material, namely metallic planar chiral nanostructures.The planar chiral structures belong to a new type of optical meta-material that have not until recently been systematically investigated [2]. PCS studied here consist of regular arrays of chiral gammadions with a groove width of about 700nm cut into a thin film of metal (100nm of gold sandwiched between two 20nm thick layers of titanium) and arranged to produce a pattern of planar 442 wallpaper group symmetry. More details on the structures may be found in [2] where we reported that they affect the polarization state of diffracted light in an enantiomerically-sensitive fashion. The failure of time reversal symmetry for optical interactions with the planar chiral structures, which we report here, are evidenced by the unusual symmetries observed in images of the structures obtained using a polarizing optical microscope. The observations were performed in reflective mode, with a white light halogen source, using a 40× microscope objective and a 6.3 megapixel low noise CMOS CCD camera. Light incident on the structure was linearly polarized and the sample was imaged throug...
Abstract:The authors have developed two distinct processes for the fabrication of mesoscopic Josephson junction qubits that are compatible with conventional CMOS processing. These devices, based on superconducting Al/A1203/AI tunnel junctions, are fabricated by electron beam lithography using single-layer and multi-layer resists. The new single-layer resist process is found to have significant advantages over conventional fabrication methods using suspended tri-layer shadow masks. It is simpler and more accurate to implement, and avoids the significant areas of redundant metallisation that are an unavoidable by-product of the tri-layer shadow mask method.
For the first time, all-dielectric planar chiral metamaterials consisting of arrays of silicon nitride gammadions on fused silica substrates have been fabricated, and shown to be capable of inducing large changes to the polarization states of transmitted light in a manner that is dependent on the two-dimensional chirality of the microstructured silicon nitride film. The polarization response is found to reverse for opposite enantiomers, and also for the same enantiomer when it is illuminated from opposite sides of the structure. In addition, the polarization states of the various diffracted beams are found to be non-reversible. These structures therefore appear to display elements of non-reciprocal behaviour. The polarization responses of complementary designs, different chiral geometries and various silicon nitride film thicknesses have also been studied. As a result we conclude that multiple reflections within the patterned silicon nitride layer play an important role in defining the mechanism by which these structures are able to modify the polarization states of diffracted light.
The polarization state of visible light is found to be altered upon reflection from artificial two-dimensional chiral media. Arrays of metallic planar chiral structures were fabricated by electron beam lithography and ion beam milling. The characteristic dimensions on the chiral elements correspond to wavelengths in the near-IR. Our chiral media are found to induce strong polarization effects, with the handedness of individual elements having a direct effect on the sense and magnitude of rotation of the diffracted light.
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