Sergej Orlov

Observation of optical polarization Möbius strips

Light with twist and structure Möbius strips are three-dimensional structures consisting of a surface with just a single side. Readily demonstrated by snipping a paper ring, adding a twist, and then joining the ends of paper together again, these structures have intriguing mathematical properties in terms of topology and geometry. Bauer et al. used a liquid crystal to engineer the wavefront of a laser beam to make an optical version of the Möbius strip by effectively “snipping and twisting” the polarization properties of the light beam. Science, this issue p. 964 An optical version of a Möbius strip has been realized. Möbius strips are three-dimensional geometrical structures, fascinating for their peculiar property of being surfaces with only one “side”—or, more technically, being “nonorientable” surfaces. Despite being easily realized artificially, the spontaneous emergence of these structures in nature is exceedingly rare. Here, we generate Möbius strips of optical polarization by tightly focusing the light beam emerging from a q-plate, a liquid crystal device that modifies the polarization of light in a space-variant manner. Using a recently developed method for the three-dimensional nanotomography of optical vector fields, we fully reconstruct the light polarization structure in the focal region, confirming the appearance of Möbius polarization structures. The preparation of such structured light modes may be important for complex light beam engineering and optical micro- and nanofabrication.

Nanointerferometric amplitude and phase reconstruction of tightly focused vector beams

. To guarantee highquality and resolution in the investigation ofobjects with sub-wavelength dimensions, the pre-cise knowledge of the spatial distribution of theexciting vectorial eld is of utmost importance.Full- eld reconstruction methods presented sofar involved, for instance, complex near- eldtechniques

Geometric spin Hall effect of light in tightly focused polarization-tailored light beams

,100401(2009)].TheunderlyingeffectisphenomenologicallysimilartothespinHalleffectoflightbutdoesnotdependonthespecificlight-matter interaction and can be interpreted as a purely geometric effect. Thus, it was named the geometricspin Hall effect of light. Here, we experimentally investigate the appearance of this effect in tightly focusedvector beams. We use an experimental nanoprobing technique in combination with a reconstruction algorithm toverify the relative shifts of the components of the electric energy density and the shift of the intensity in the focalplane. By that, we experimentally demonstrate the geometric spin Hall effect of light in a highly nonparaxialbeam.DOI: 10.1103/PhysRevA.89.013840 PACS number(s): 42

Interaction of highly focused vector beams with a metal knife-edge

We investigate the interaction of highly focused linearly polarized optical beams with a metal knife-edge both theoretically and experimentally. A high numerical aperture objective focuses beams of various wavelengths onto samples of different sub-wavelength thicknesses made of several opaque and pure materials. The standard evaluation of the experimental data shows material and sample dependent spatial shifts of the reconstructed intensity distribution, where the orientation of the electric field with respect to the edge plays an important role. A deeper understanding of the interaction between the knife-edge and the incoming highly focused beam is gained in our theoretical model by considering eigenmodes of the metal-insulator-metal structure. We achieve good qualitative agreement of our numerical simulations with the experimental findings.

Corrections to the knife-edge based reconstruction scheme of tightly focused light beams

The knife-edge method is an established technique for profiling light beams. It was shown, that this technique even works for tightly focused beams, if the material and geometry of the probing knife-edges are chosen carefully. Furthermore, it was also reported recently that this method fails, when the knife-edges are made from pure materials. The artifacts introduced in the reconstructed beam shape and position depend strongly on the edge and input beam parameters, because the knife-edge is excited by the incoming beam. Here we show, that the actual beam shape and spot size of tightly focused beams can still be derived from knife-edge measurements for pure edge materials and different edge thicknesses by adapting the analysis method of the experimental data taking into account the interaction of the beam with the edge.

Engineered disorder and light propagation in a planar photonic glass.

The interaction of light with matter strongly depends on the structure of the latter at wavelength scale. Ordered systems interact with light via collective modes, giving rise to diffraction. In contrast, completely disordered systems are dominated by Mie resonances of individual particles and random scattering. However, less clear is the transition regime in between these two extremes, where diffraction, Mie resonances and near-field interaction between individual scatterers interplay. Here, we probe this transitional regime by creating colloidal crystals with controlled disorder from two-dimensional self-assembly of bidisperse spheres. Choosing the particle size in a way that the small particles are transparent in the spectral region of interest enables us to probe in detail the effect of increasing positional disorder on the optical properties of the large spheres. With increasing disorder a transition from a collective optical response characterized by diffractive resonances to single particles scattering represented by Mie resonances occurs. In between these extremes, we identify an intermediate, hopping-like light transport regime mediated by resonant interactions between individual spheres. These results suggest that different levels of disorder, characterized not only by absence of long range order but also by differences in short-range correlation and interparticle distance, exist in colloidal glasses.

Influence of the substrate material on the knife-edge based profiling of tightly focused light beams

The performance of the knife-edge method as a beam profiling technique for tightly focused light beams depends on several parameters, such as the material and height of the knife-pad as well as the polarization and wavelength of the focused light beam under study. Here we demonstrate that the choice of the substrate the knife-pads are fabricated on has a crucial influence on the reconstructed beam projections as well. We employ an analytical model for the interaction of the knife-pad with the beam and report good agreement between our numerical and experimental results. Moreover, we simplify the analytical model and demonstrate, in which way the underlying physical effects lead to the apparent polarization dependent beam shifts and changes of the beamwidth for different substrate materials and heights of the knife-pad.

Towards an optical far-field measurement of higher-order multipole contributions to the scattering response of nanoparticles

We experimentally show an all-optical multipolar decomposition of the lowest-order eigenmodes of a single gold nanoprism using azimuthally and radially polarized cylindrical vector beams. By scanning the particle through these tailored field distributions, the multipolar character of the eigenmodes gets encoded into 2D-scanning intensity maps even for higher-order contributions to the eigenmode that are too weak to be discerned in the direct far-field scattering response. This method enables a detailed optical mode analysis of individual nanoparticles.

Balancing ballistic and hopping light transport by purposive arraying of colloidal particles

Ordered and disordered monolayers of spheres were assembled on dielectric and metallized substrate using the Langmuir-Blodgett style technique. The coexistence of Mie and diffraction resonances was investigated. Experiments showed the weak dependence of diffraction resonances on the distance between spheres, but their gradual destruction with increasing disorder. In turn, Mie resonances appear along the increased light localization in the monolayer, but experience strong blue shift and gradual reduction of the magnitude along the increased isolation in the lattice. Calculation proved that hybridization of Mie resonances rapidly vanishes along the increase of the spacing between spheres and the hopping of excitations between spheres can be expected only in tightly packed arrays.

Reconstruction of tightly focused beams using Mie-scattering

By using a sub-wavelength nano-particle as a field probe and a tailored detection scheme we are able to reconstruct the electric energy density in the focal plane of a high numerical aperture focusing system.