2017, Zeisberger, Matthias, Schneidewind, Henrik, Hübner, Uwe, Popp, Jürgen, Schmidt, Markus A.

Metasurfaces have revolutionized photonics due to their ability to shape phase fronts as requested and to tune beam directionality using nanoscale metallic or dielectric scatterers. Here we reveal inverse metasurfaces showing superior properties compared to their positive counterparts if transmission mode operation is considered. The key advantage of such slot-type metasurfaces is the strong reduction of light in the parallel-polarization state, making the crossed-polarization, being essential for metasurface operation, dominant and highly visible. In the experiment, we show an up to four times improvement in polarization extinction for the individual metasurface element geometry consisting of deep subwavelength nanoboomerangs with feature sizes of the order of 100 nm. As confirmed by simulations, strong plasmonic hybridization yields two spectrally separated plasmonic resonances, ultimately allowing for the desired phase and scattering engineering in transmission. Due to the design flexibility of inverse metasurfaces, a large number of highly integrated ultra-flat photonic elements can be envisioned, examples of which include monolithic lenses for telecommunications and spectroscopy, beam shaper or generator for particle trapping or acceleration or sophisticated polarization control for microscopy.

2014, Hübner, Uwe, Popp, Jürgen

[no abstract available]

2017, Obst, Lieselotte, Göde, Sebastian, Rehwald, Martin, Brack, Florian-Emanuel, Branco, Joao, Bock, Stefan, Bussmann, Michael, Cowan, Thomas E., Curry, Chandra B., Fiuza, Frederico, Gauthier, Maxence, Gebhardt, Rene, Helbig, Uwe, Huebl, Axel, Hübner, Uwe, Irman, Arie, Kazak, Lev, Kim, Jongjin B., Kluge, Thomas, Kraft, Stephan, Löser, Markus, Metzkes, Josefine, Mishra, Rohini, Rödel, Christian, Schlenvoigt, Hans-Peter, Siebold, Mathias, Tiggesbäumker, Josef, Wolter, Steffen, Ziegler, Tim, Schramm, Ulrich, Glenzer, Siegfried H., Zeil, Karl

We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150 TW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20 MeV with particle numbers exceeding 109 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (∅ 5 μm) and planar (20 μm × 2 μm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions.

2017, Pacakova, Barbara, Verhagen, Timotheus, Bousa, Milan, Hübner, Uwe, Vejpravova, Jana, Kalbac, Martin, Frank, Otakar

We present an approach that allows for the preparation of well-defined large arrays of graphene wrinkles with predictable geometry. Chemical vapor deposition grown graphene transferred onto hexagonal pillar arrays of SiO2 with sufficiently small interpillar distance forms a complex network of two main types of wrinkle arrangements. The first type is composed of arrays of aligned equidistantly separated parallel wrinkles propagating over large distances, and originates from line interfaces in the graphene, such as thin, long wrinkles and graphene grain boundaries. The second type of wrinkle arrangement is composed of non-aligned short wrinkles, formed in areas without line interfaces. Besides the presented hybrid graphene topography with distinct wrinkle geometries induced by the pre-patterned substrate, the graphene layers are suspended and self-supporting, exhibiting large surface area and negligible doping effects from the substrate. All these properties make this wrinkled graphene a promising candidate for a material with enhanced chemical reactivity useful in nanoelectronic applications.