Observation of photonic constant-intensity waves and induced transparency in tailored non-Hermitian lattices.

Light propagation is strongly affected by scattering due to imperfections in the complex medium. It has been recently theoretically predicted that a scattering-free transport through an inhomogeneous medium is achievable by non-Hermitian tailoring of the complex refractive index. Here, we implement photonic constant-intensity waves in an inhomogeneous, linear, discrete mesh lattice.

Transforming Space with Non-Hermitian Dielectrics.

Coordinate transformations are a versatile tool to mold the flow of light, enabling a host of astonishing phenomena such as optical cloaking with metamaterials. Moving away from the usual restriction that links isotropic materials with conformal transformations, we show how nonconformal distortions of optical space are intimately connected to the complex refractive index distribution of an isotropic non-Hermitian medium. Remarkably, this insight can be used to circumvent the material requirement of working with refractive indices below unity, which limits the applications of transformation optics.

Detecting chirality in mixtures using nanosecond photoelectron circular dichroism.

We report chirality detection of structural isomers in a gas phase mixture using nanosecond photoelectron circular dichroism (PECD). Combining pulsed molecular beams with high-resolution resonance enhanced multi-photon ionization (REMPI) allows specific isolated transitions belonging to distinct components in the mixture to be targeted.

High-resolution resonance-enhanced multiphoton photoelectron circular dichroism.

Photoelectron circular dichroism (PECD) is a highly sensitive enantiospecific spectroscopy for studying chiral molecules in the gas phase using either single-photon ionization or multiphoton ionization. In the short pulse limit investigated with femtosecond lasers, resonance-enhanced multiphoton ionization (REMPI) is rather instantaneous and typically occurs simultaneously via more than one vibrational or electronic intermediate state due to limited frequency resolution. In contrast, vibrational resolution in the REMPI spectrum can be achieved using nanosecond lasers.

Phase-Modulated Scattering Manipulation for Exterior Cloaking in Metal-Dielectric Hybrid Metamaterials.

Artificially structured metamaterials with metallic or dielectric inclusions are extensively studied for exotic light manipulations via controlling the local-resonant modes in the microstructures. The coupling between these resonant modes has drawn growing interest in recent years due to the advanced functional metamaterial making the microstructures more and more complex. Here, the suppression of magnetic resonance of a dielectric cuboid, an analogue to the scattering cancellation effect or radiation control system, realized with an exterior cloaking in a hybrid metamaterial system, is demonstrated.

Nonlinearity in the Dark: Broadband Terahertz Generation with Extremely High Efficiency.

Plasmonic metamaterials and metasurfaces offer new opportunities in developing high performance terahertz emitters and detectors beyond the limitations of conventional nonlinear materials. However, simple meta-atoms for second-order nonlinear applications encounter fundamental trade-offs in the necessary symmetry breaking and local-field enhancement due to radiation damping that is inherent to the operating resonant mode and cannot be controlled separately. Here we present a novel concept that eliminates this restriction obstructing the improvement of terahertz generation efficiency in nonlinear metasurfaces based on metallic nanoresonators.

Ultrahigh-Density Spin-Polarized H and D Observed via Magnetization Quantum Beats.

We measure nuclear and electron spin-polarized H and D densities of at least 10^{19}  cm^{-3} with ∼10  ns lifetimes, from the photodissociation of HBr and DI with circularly polarized UV light pulses. This density is ∼6 orders of magnitude higher than that produced by conventional continuous-production methods and, surprisingly, at least 100 times higher than expected densities for this photodissociation method. We observe the hyperfine quantum beating of the H and D magnetization with a pickup coil, i.

Tailorable Zero-Phase Delay of Subwavelength Particles toward Miniaturized Wave Manipulation Devices.

Adjustable zero-phase delay and equiphase control are demonstrated in single and multilayer dielectric particle arrays with high index and low loss. The polarization-independent near-zero permeability is the origin of the wave control near the first Mie magnetic resonance. The proposed design paves the way for subwavelength devices and opens up new avenues for the miniaturization and integration of THz and optical components.

Large quality factor in sheet metamaterials made from dark dielectric meta-atoms.

Metamaterials--or artificial electromagnetic materials--can create media with properties unattainable in nature, but mitigating dissipation is a key challenge for their further development. Here, we demonstrate a low-loss metamaterial by exploiting dark bound states in dielectric inclusions coupled to the external waves by small nonresonant metallic antennas. We experimentally demonstrate a dispersion-engineered metamaterial based on a meta-atom made from alumina, and we show that its resonance has a much larger quality factor than metal-based meta-atoms.

Broadband terahertz generation from metamaterials.

The terahertz spectral regime, ranging from about 0.1-15 THz, is one of the least explored yet most technologically transformative spectral regions. One current challenge is to develop efficient and compact terahertz emitters/detectors with a broadband and gapless spectrum that can be tailored for various pump photon energies.

Defect-induced defect-mediated magnetism in ZnO and carbon-based materials.

The recent discovery of magnetism in a variety of diverse non-magnetic materials containing defects has challenged conventional thinking about the microscopic origin of magnetism in general. Especially intriguing is the complete absence of d electrons that are traditionally associated with magnetism. By a systematic microscopic investigation of two completely dissimilar materials (namely, ZnO and rhombohedral-C(60) polymers) exhibiting ferromagnetism in the presence of defects, we show that this new phenomenon has a common origin and the mechanism responsible can be used as a powerful tool for inducing and tailoring magnetic features in systems which are not magnetic otherwise.

The laser-induced discoloration of stonework; a comparative study on its origins and remedies.

For understanding the phenomena associated with the discoloration observed in some cases of infrared laser cleaned stonework surfaces, a comparative study of three different types and morphologies of pollution encrustation and stone substrates was undertaken. Fragments originating from monuments with historic and/or artistic value, bearing homogeneous thin soiling on Pentelic marble (Athens, Greece), thick encrustation on Hontoria limestone (Burgos, Spain) and compact thin crust on gypsum decorations (Athens, Greece), have been studied on the basis of their composition and origin, together with the conditions that may induce yellowing effects upon their laser cleaning with IR wavelengths. While irradiation in the UV (i.

Photophysical characterization of hematoporphyrin incorporated within collagen gels.

Physical properties of hematoporphyrin-enriched collagen gels relevant to the photodynamic treatment of cancer are characterized. The incorporation of the sensitizer within the gels does not affect either the structure of the gel or the absorption and fluorescence spectra of the sensitizer. The gel-embedded sensitizer photodegrades efficiently with the formation of a product emitting near 635 nm.