Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.

Topological Photonics

Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase, modifying electronic properties, modulating magnetism as well as tuning emission properties. Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF(4) nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF(4) upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels to volumetric three-dimensional displays.

Simultaneous phase and size control of upconversion nanocrystals through lanthanide doping

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

The remagnetization process after ultrafast demagnetization can be described by relaxation mechanisms between the spin, electron, and lattice reservoirs. Thereby, collective spin excitations in form of spin waves and their angular momentum transfer play an important role on the longer timescales. In this work, we address the question whether the strength of demagnetization affects the coherency and the phase of the excited spin waves. We present a study of coherent magnetization dynamics in thin nickel films after ultrafast demagnetization using the all-optical, time-resolved magneto-optical Kerr-effect (tr-MOKE) technique. The largest coherent oscillation amplitude was observed for strongly quenched systems, showing the conservation of coherency for demagnetizations of up to 90%. Moreover, the phase of the excited spin-waves increases with pump power, indicating a delayed start of the precession during the remagnetization.

Coherent magnetization dynamics in strongly quenched Ni thin films

Verfahren zur Herstellung von Photonischen Kristallen mit den Verfahrensschritten A process for producing photonic crystals comprising the steps of a) Bereitstellen eines anorganischen Photoresists, der bei Belichtung mit einer Photonenergie, die groser als die elektronische Bandlucke des Photoresists ist, eine Phasenanderung zeigt und der einen Brechungssindex oberhalb von 2,0 aufweist a) providing an inorganic photoresist which a Brechungssindex above 2.0 which upon exposure to a photon energy which is greater than the electronic band gap of the photoresist, a phase change, and shows the b) Belichten des Photoresists mit einem fokussierten Laserstrahl, dessen Photonenergie geringer ist als die elektronische Bandlucke des Photoresists, dessen Intensitat im Brennpunkt aber so hoch ist, dass dort nichtlineare Effekte auftreten, wodurch im Photoresist eine Phasenanderung auftritt, b) exposing the photoresist with a focused laser beam whose photon energy is lower than the electronic band gap of the photoresist, but whose intensity at the focal point is so high that nonlinear effects occur there, which in the photoresist, a phase change occurs, c) mehrfaches Bewegen des Laserstrahls und des Photoresists relativ zueinander und Wiederholen des Verfahrensschritts b), c) multiple moving the laser beam and the photoresist relative to each other and repeating the process step b), d) Entwickeln des belichteten Photoresists in einer Atzlosung, die bevorzugt eine Phase des Photoresists lost, d) developing the exposed photoresist in an etching solution which preferably dissolves one phase of the photoresist, e) Entnehmen des entwickelten Photoresists als Photonischer Kristall. e) removing the developed photoresist as a photonic crystal.

Verfahren zur Herstellung von Photonischen Kristallen A process for producing photonic crystals

Die vorliegende Erfindung betrifft eine Vorrichtung zur S-Parameter Charakterisierung von elektrischen Bauelementen, bei welchen eine Strahlungsquelle (001) ein Emitter (101) nachgeordnet ist, welcher an ein elektronisches Bauteil (121) angekoppelt und mit einem Detektor (111) verbunden ist sowie ein Verfahren zur Charakterisierung der S-Parameter des elektronischen Bauteils sowie die Verwendung der Vorrichtung in dem genannten Verfahren. The present invention relates to a device for the S-parameter characterization of electrical components, in which a radiation source (001) is arranged downstream of an emitter (101) coupled which at an electronic component (121) and a detector (111) is connected and a A method for characterizing the S parameters of the electronic component as well as the use of the apparatus in the said method.

Vorrichtung und Verfahren zur S- Parameter-Charakterisierung von optoelektronischen Bauelementen Apparatus and method for S-parameter characterization of optoelectronic devices

Quantum-inspired terahertz sensing using nonlinear interferometers enables detection of terahertz spectral properties while only measuring visible light, which never interacted with the sample. Applications in spectroscopy and thickness determination are presented.

Quantum-Inspired Terahertz Sensing

We show that photonic-crystal environments can create symmetry-specific bandgaps that host a wide variety of symmetry-protected lines of bound states in the continuum, which we prove to be impossible in homogeneous environments.

Georg von Freymann

Papers

Coherent magnetization dynamics in strongly quenched Ni thin films

Verfahren zur Herstellung von Photonischen Kristallen A process for producing photonic crystals

Vorrichtung und Verfahren zur S- Parameter-Charakterisierung von optoelektronischen Bauelementen Apparatus and method for S-parameter characterization of optoelectronic devices

Quantum-Inspired Terahertz Sensing

Using symmetry bandgaps to create bound states in the continuum in 3D photonic crystals