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Nanocolloids that are cumulatively referred to as nanocarbons, attracted significant attention during the last decade because of facile synthesis methods, water solubility, tunable photoluminescence, easy surface modification, and high biocompatibility. Among the latest development in this reserach area are chiral nanocarbons exemplified by chiral carbon dots (CDots). They are expected to have applications in sensing, catalysis, imaging, and nanomedicine. However, the current methods of CDots synthesis show often contradictory chemical/optical properties and structural information that required a systematic study with careful structural evaluation. Here, we investigate and optimize chiroptical activity and photoluminescence of L- and D-CDots obtained by hydrothermal carbonization of L- and D-cysteine, respectively. Nuclear magnetic resonance spectroscopy demonstrates that they are formed via gradual dehydrogenation and condensation reactions of the starting amino acid leading to particles with a wide spectrum of functional groups including aromatic cycles. We found that the chiroptical activity of CDots has an inverse correlation with the synthesis duration and temperature, whereas the photoluminescence intensity has a direct one, which is associated with degree of carbonization. Also, our studies show that the hydrothermal synthesis of cysteine in the presence of boric acid leads to the formation of CDots rather than boron nitride nanoparticles as was previously proposed in several reports. These results can be used to design chiral carbon-based nanoparticles with optimal chemical, chiroptical, and photoluminescent properties.

We have grown arrays of silver nanowires in pores of anodic alumina membranes (metamaterials with hyperbolic dispersion at λ ≥ 615 nm), spin coated them with the dye-doped polymer (HITC:PMMA), and studied the rates of radiative and nonradiative relaxation as well as the concentration quenching (Förster energy transfer to acceptors). The results were compared to those obtained on top of planar Ag films and glass (control samples). The strong spatial inhomogeneity of emission kinetics recorded in different spots across the sample and strong inhibition of the concentration quenching in arrays of Ag nanowires are among the most significant findings of this study.

We have studied reflection spectra of dye-doped and undoped polymers deposited onto Ag and Au substrates and found anomalous dips in the UV spectral range. On top of Ag substrates, the λ ∼ 375 nm dips were observed in undoped PMMA, PVP, and PS polymers as well as PMMA doped with Rh590 and HITC laser dyes. In silver-based samples, the spectral positions of the observed reflection dips were close to singularities in the refractive indexes of surface plasmon polaritons (SPPs) propagating at the interface between Ag and polymer. The latter singularities can tentatively explain the λ ∼ 375 nm reflection dips, if the scattering of Ag and polymeric films is large enough to launch SPP without any prism or grating. The dips observed in reflection of Rh590:PMMA and HITC:PMMA on top of Au, were more pronounced than those on Ag, broader, shifted to shorter wavelengths, and their spectral positions had large standard deviations. Furthermore, no anomalous dips in gold-based samples were observed in the reflection spectra of undoped PMMA, PVP, and PS polymers, and a modest singularity in the SPP refractive index, predicted theoretically at λ ∼ 500 nm, cannot explain the dips in the UV reflection spectra observed experimentally. It appears likely that the origin of the reflection dips on top of Au substrates is different from that on top of Ag substrates.

We have studied the effects of planar, lamellar, and random nanostructured metal-dielectric environments on spontaneous emission and energy transfer concentration quenching of HITC laser dye. We found an inhibition of the concentration quenching in vicinity of metal, which was stronger in nanostructured substrates than in plain geometries. It was shown that the same substrates, which boosted spontaneous emission, also inhibited the concentration quenching. The effect is discussed in terms of the Forster radius affected by losses. Work at LLNL was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344

Mie-resonant high-index dielectric nanoparticles and metasurfaces have been suggested as a viable platform for enhancing both electric and magnetic dipole transitions of fluorescent emitters. While the enhancement of the electric dipole transitions by such dielectric nanoparticles has been demonstrated experimentally, the case of magnetic-dipole transitions remains largely unexplored. Here, we study the enhancement of spontaneous emission of Eu3+ ions, featuring both electric and magnetic-dominated dipole transitions, by dielectric metasurfaces composed of Mie-resonant silicon nanocylinders. By coating the metasurfaces with a layer of an Eu3+ doped polymer, we observe an enhancement of the Eu3+ emission associated with the electric (at 610 nm) and magnetic-dominated (at 590 nm) dipole transitions. The enhancement factor depends systematically on the spectral proximity of the atomic transitions to the Mie resonances as well as their multipolar order, both controlled by the nanocylinder size. Importantly, the branching ratio of emission via the electric or magnetic transition channel can be modified by carefully designing the metasurface, where the magnetic dipole transition is enhanced more than the electric transition for cylinders with radii of about 130 nm. We confirm our observations by numerical simulations based on the reciprocity principle. Our results open new opportunities for bright nanoscale light sources based on magnetic transitions.

We demonstrated amplified spontaneous emission (ASE) enabled by evanescent gain at an interface between two adjacent dielectrics. The ASE wave is outcoupled to the high-index medium at the critical angle, enabling observation of spectacular emission rings.

We report on the optical properties of nanoporous gold leaf (NPGL) metamaterials consisting of single and multiple-fold layers, and having different pore and ligament sizes. Due to their complex structure, such metamaterials have a unique optical property, which distinguishes them from homogeneous gold films. Thus, the transmission spectra of NPGLs feature two characteristic peaks positioned at ~ 490 nm and ~560 nm to 605 nm. The most notable result of this study is that the optical properties of NPGLs can be tuned by changing the dielectric environment and by applying voltage in an electrochemical cell.

We found that inhibition of concentration quenching of HITC dye in Fabry-Perot cavities is almost similar to that on top of silver. Low convexity of the emission kinetics suggests strong coupling mediated by surface plasmons.

We have studied spectra and angular distribution of emission of Rhodamine 6G dye in Fabry-Perot cavities in weak and strong coupling regimes and demonstrated control of the strong coupling with the pumping intensity.

Broadband plasmonic absorbers are essential components for photovoltaic, photothermal, and light-emitting devices. They are often made by lithographic processes that impart out-of-plane surface features with subwavelength dimensions to metallic films. However, lithographic subwavelength patterning of inexpensive plasmonic ceramics, such as TiN, is challenging because of high-temperature processing and the chemical robustness of these materials. In this work, we show that layer-by-layer assembly (LbL) of TiN plasmonic nanoparticles with polyelectrolytes results in spontaneous formation of out-of-plane topography with subwavelength dimensions. The columnar morphology of these corrugated coatings and their plasmonic functionality results in broadband absorption capabilities exemplified by 90% of the light from the ultraviolet to infrared parts of the spectrum being absorbed. The method is applicable to large, flexible, and conformal surfaces with complex geometry. It is also fast, scalable, and environmental...

We have demonstrated amplified spontaneous emission (ASE) propagating along the planar interface between two adjacent dielectrics with slightly different refractive indexes. This emission originates from the leaky mode, fueled by optical gain in the low-index dielectric, that is outcoupled to the high-index dielectric in vicinity of the critical angle for total internal reflection. This led us to the observation of spectacular concentric rings of ASE emission occurring above the low and soft stimulated emission threshold. The results of our study can be used to develop novel miniature low-threshold stimulated emission sources and photonic circuits operating at optical frequencies.

The Kirchhoff law of thermal radiation, relating emissivity {\epsilon} and absorptance {\alpha}, has been originally formulated for opaque bodies in thermodynamic equilibrium with the environment. However, in many systems of practical importance, both assumptions are often not satisfied. In this work, we revisit the century-old law and examine the limits of its applicability in an example of Er:YAG and Er:YLF dielectric crystals, potential radiation converters for thermophotovoltaic applications. In our experiments, the (80 at.%) Er:YAG crystal was opaque between 1.45 {\mu}m and 1.64 {\mu}m. In this spectral range, its absorptance {\alpha}({\lambda}) is spectrally flat and differentiates from unity only by a small amount of reflection. The shape of the emissivity spectrum {\epsilon}({\lambda}) closely matches that of absorptance {\alpha}({\lambda}), suggesting that the Kirchhoff law can adequately describe thermal radiation of opaque bodies, even if the requirement of thermodynamic equilibrium is not satisfied. The(20 at.%) Er:YLF crystal had smaller size, lower concentration of Er ions, and it was not opaque. Nevertheless, its spectrum of emissivity {\epsilon}({\lambda}) had almost the same shape (between 1.45 {\mu}m and 1.62 {\mu}m) as the spectrum of absorptance {\alpha}({\lambda}) derived from the transmission measurements. This observation is in line with our prediction that the spectra of emissivity and absorptance should have identical shapes in optically thin slabs. We, thus, show that the Kirchhoff law of thermal radiation can be extended (with caution) even to not-opaque bodies away from the thermodynamic equilibrium.

Recent years have seen an increase of interest in developing nano-scale sources of coherent radiation. Numerous schemes includes novel confinement techniques such as plasmons and micro resonators as well as novel materials, such as two-dimensional transition metal di-chalcogenides have been investigated. In the process a lot of confusion has been produced by introduction into consideration of numerous parameters such as Purcell factor and the beta (fraction of spontaneous emission going into a given mode). That confusion makes comparative analysis of miniature lasers difficult. In this talk we show that the only parameters defining the laser threshold are the modal loss, quantum efficiency and physical volume of gain medium. Using this method we compare the novel lasers with existing state of the art – DFB and VCSELs and draw conclusions.

Mie-resonant high-index dielectric nanoparticles and metasurfaces have been suggested as a viable platform for enhancing both electric and magnetic dipole transitions of fluorescent emitters. While the enhancement of the electric dipole transitions by such dielectric nanoparticles has been demonstrated experimentally, the case of magnetic-dipole transitions remains largely unexplored. Here, we study the enhancement of spontaneous emission of Eu

A very brief tribute to Mark I. Stockman and his contributions to optical science.

We have studied emission kinetics in dye-doped polymeric films (HITC:PMMA), deposited on top of glass and silver and embedded in Fabry–Perot cavities (metal-insulator-metal waveguides). For highly doped films on glass, we observed strong concentration quenching, as evidenced by a dramatic shortening of the emission kinetics, consistent with our previous studies. However, for the same dye-doped films on top of silver, slower emission kinetics were observed despite the high decay rates of individual dye molecules near the metallic surface. The concentration quenching rates in Fabry–Perot cavities were nearly identical to those of HITC:PMMA films deposited on top of silver. These findings are explained within a theoretical model for the inhibition of Förster energy transfer near a metallic surface. Furthermore, the emission kinetics of the dye-doped films on top of silver were approximately single exponential—consistent with the strong coupling of excited molecules with propagating surface plasmons.

Rapidly evolving fields of biomedical, energy, and (opto)electronic devices bring forward the need for deformable conductors with constantly rising benchmarks for mechanical properties and electronic conductivity. The search for conductors with improved strength and strain have inspired the multiple studies of nanocomposites and amorphous metals. However, finding conductors that defy the boundaries of classical materials and exhibit simultaneously high strength, toughness, and fast charge transport while enabling their scalable production, remains a difficult materials engineering challenge. Here, composites made from aramid nanofibers (ANFs) and gold nanoparticles (Au NPs) that offer a new toolset for engineering high strength flexible conductors are described. ANFs are derived from Kevlar macrofibers and retain their strong mechanical properties and temperature resilience. Au NPs are infiltrated into a porous, free-standing aramid matrix, becoming aligned on ANFs, which reduces the charge percolation threshold and facilitates charge transport. Further thermal annealing at 300 °C results in the Au-ANF composites with an electrical conductivity of 1.25 × 104 S cm−1 combined with a tensile strength of 96 MPa, a Young's modulus of 5.29 GPa, and a toughness of 1.3 MJ m−3. These parameters exceed those of most of the composite materials, and are comparable to those of amorphous metals but have no volume limitations. The plasmonic optical frequencies characteristic for constituent NPs are present in the composites with ANFs enabling plasmon-based optoelectronic applications.

We have studied emission kinetics of HITC laser dye on top of glass, smooth Au films, and randomly structured porous Au nanofoams. The observed concentration quenching of luminescence of highly concentrated dye on top of glass (energy transfer to acceptors) and the inhibition of the concentration quenching in vicinity of smooth Au films were in accord with our recent findings. Intriguingly, the emission kinetics recorded in different local spots of the Au nanofoam samples had a spread of the decay rates, which was large at low dye concentrations and became narrower with increase of the dye concentration. We infer that in different subvolumes of Au nanofoams, HITC molecules are coupled to the nanofoams weaker or stronger. The inhibition of the concentration quenching in Au nanofoams was stronger than on top of smooth Au films. This was true for all weakly and strongly coupled subvolumes contributing to the spread of the emission kinetics. The experimental observations were explained using theoretical model accounting for change in the F&ouml, rster radius caused by the strong energy transfer to metal.

We have studied spectra and angular distribution of emission in Fabry–Perot cavities formed by two silver mirrors separated by a layer of poly (methyl methacrylate) polymer doped with rhodamine 6G (R6G) dye in low ( 20 g / l ) and high ( 200 g / l ) concentrations. The frequency of emission radiated to a cavity mode was larger at large outcoupling angles—the “rainbow” effect. At the same time, the angle of the strongest emission was also determined by the cavity size: the larger the cavity, the larger the angle. The angular distribution of emission is commonly dominated by two symmetrical lobes (located at the intersection of the three-dimensional emission cone with a horizontal plane) pointing to the left and to the right of the normal to the sample. Despite the strong Stokes shift in R6G dye, the branch of the cavity dispersion curve obtained in the emission experiment is positioned above the one obtained in the reflection (extinction) experiment. Some dye molecules are poorly coupled to cavity modes. Their emission has very broad angular distribution with the maximum at θ = 0 ∘ . The signatures of strong cavity–exciton coupling were observed at high dye concentration ( 200 g / l ) but not at low concentration ( 20 g / l ). The evidence of the effect of strong coupling on emission is exemplified by a strong difference in the angular distribution of emission in two almost identical cavities, one with and another without strong coupling. Most importantly, we have demonstrated the possibility to control the ground state concentration, the coupling strength, and the dye emission spectra with Q-switched laser pulses.

We have studied poly(methyl methacrylate) (PMMA) films doped with rhodamine 6G and rhodamine B laser dyes as potential nonlinear material components for nanophotonics. For both dyes, the optimal concentrations, at which the emission excited via the two-photon-absorption (TPA) process is maximized, have been determined. Despite relatively large values of TPA cross sections obtained in this study, the characteristic pumping densities needed to observe pronounced nonlinear effects substantially exceed the laser damage threshold for Au or alternative plasmonic materials. This makes the studied laser dyes unsuitable for some of the intended nanophotonics applications.

We have studied, both theoretically and experimentally, the excitation of volume modes in a lamellar metal/dielectric metamaterial with hyperbolic dispersion. The highly efficient light penetration through tens of metamaterial layers is consistent with a relatively low propagation loss. The volume modes were found to be highly sensitive to the surface roughness of the layers, which can be a detrimental factor in device applications.

Enhancing electrical conductance in organic semiconductors has been a focus of intense research over last few decades. The improvement can be made by optimizing either the material or the device architecture. As it has been shown in [Orgiu et al., Nature Materials, 2015], strong coupling of organic molecules with a nanostructured plasmonic substrate can significantly improve the molecules’ electrical conductivity. In the present study, we searched for the effect of strong coupling with a Fabry-Perot cavity on the conductivity of the semiconducting Poly (3- hexylthiophene) (P3HT) polymer. Despite the observation of the strong coupling evidenced by a very large Rabi splitting of 1.0 eV, the increase of electrical conductivity with increase of the P3HT film thickness was primarily affected by an increase of the polymer’s order in thick P3HT films.

The objective of this study was to control the transmission, dispersion and, eventually, the nonlinearity of an optical fiber by intercepting and manipulating the evanescent field extending from the core to the cladding with a variety of plasmonic and metamaterial nanostructures. The access to evanescent waves is enabled by placing the core close to the flat surface of the cladding in the so-called D-shaped fiber design. In the first phase of the project, reported here, the numerical simulations of D-shaped fibers with deposited metal (Au) have been performed. We, furthermore, demonstrated that the fiber transmission can be controlled by highly concentrated rhodamine 6G molecules deposited onto the fiber’s flat surface.

We have observed directional spontaneous emission of rhodamine 6G dye deposited on top of a silver grating and found that its angular distribution patterns were very different in TE and TM polarizations. The latter was related to the dispersion curves determined based on the polarized reflection spectra measured at multiple incidence angles. The most intriguing finding of this Letter was a resonance, which was coupled with TE-polarized light and determined the characteristic double-crescent patterns in the TE-polarized spontaneous emission. This observation, as well as nearly similar resonance observed in TM polarization, was tentatively explained in terms of leaky waveguide modes supported by a film of dye-doped polymer.

The long-range inhibition of the luminescence concentration quenching in heavily doped HITC:PMMA polymeric films in the vicinity of lamellar hyperbolic metamaterials and metallic surfaces is tentatively explained in terms of the strong exciton-plasmon coupling.

We have demonstrated the novel low-threshold surface-emitting plasmonic laser and explained its performance in terms of the distributed feedback mechanism, providing a new degree of freedom to the laser design.

We have observed double crescent patterns in the TE polarized spontaneous emission of rhodamine 6G dye deposited onto silver grating metasurface. It originates from the surface wave characterized by the effective index of refraction n=1.03.

In example of Fabry-Perot cavities filled with dye molecules, we studied a range of strong coupling phenomena in complex systems with multiple exciton and optical resonances, bringing applications of these exciting systems one step closer.

We have demonstrated that the stimulated emission of surface plasmons propagating on top of multilayered hyperbolic metamaterials coated with dye-doped polymeric films has a much lower (2.5–7 times) threshold than that on top of thick Ag films. This observation correlates with more than 2-fold shortening of the spontaneous emission kinetics on top of a lamellar metamaterial as compared to that on top of silver. The propagation of surface plasmons on top of the metamaterial and silver substrates was modeled (in the Otto geometry) using COMSOL Multiphysics. It has been shown that at given system parameters, the plasmon propagation loss in a metamaterial is smaller than that in silver by ∼14% and cannot explain the dramatic reduction of the lasing threshold observed experimentally in the metamaterial samples. We infer that the stimulated emission of propagating plasmons on top of a metamaterial is enhanced by the nonlocal dielectric environment and high local density of photonic states.

A possibility to tune optical properties of materials on demand is of great importance to both fundamental science and applications. We show that nanosecond laser pumping can significantly depopulate the ground state of AF455 dye nanoparticles, resulting in gigantic change of dielectric permittivity of the order of unity. Such extreme nonlinearity (χ(3) = 1.3 × 10–5 esu), evidenced by increase of the Mie scattering efficiency, places AF455 dye among the most efficient χ(3) nonlinear optical materials, extends the limits of active metamaterials and plasmonics, and paves the way to ultimate control of photonic devices and systems.

Discussions.-- et al.

Optical characterization of subwavelength objects is important for biology, nanotechnology, chemistry, and materials science. Unfortunately, the information about interaction of an isolated subwavelength object with light is contained in evanescent waves that exponentially decay away from the source. Numerous techniques have been proposed to access or restore this information. In interscale mixing microscopy (IMM), a diffraction grating positioned in the near field proximity of the object is used to convert the originally-evanescent waves into propagating modes that can be detected with far-field measurements. However, far-field signal needs to be post-processed to un-couple the diffraction-limited and subwavelength responses. Several techniques, based on multiple measurements, have been previously proposed. Here, we show that with simple Fourier-transform based post processing can be used to characterize position, and optical size of the object based on a single measurement. To verify the proposed formalism, three finite diffraction gratings were fabricated. Two of these gratings contained pre-engineered “defects” that played the role of “unknown objects”, while the remaining grating was used as a reference. We demonstrate that we can identify the position and size of ~wavelength/10 object with far-field characterization. The same measurement provides a platform to analyze optical spectrum of the object. Although demonstrated in this work on example of 1D grating, IMM can be extended to 2D subwavelength imaging

The functionalities of traditional optical component are mainly based on the phase accumulation through the propagation length, leading to a bulky optical component such as converging lens and waveplate. Metasurfaces composed of planar structures with artificial design have attracted a huge number of interests due to their ability on controlling the electromagnetic phase as well as amplitude at a subwavelength scale. The feasible applications based on metasurfaces include nonlinear dynamics, light beam shaping, quantum interference etc. Beside those promising characteristics, people now intend to discover the field of meta-devices, where we can attain optical properties and functionalities through changing the feature characteristics of metasurfaces in demand. They therefore pave a potential way for the development of flat optical devices and integrated optoelectronic systems and toward the far-reaching applications which are impossible previously. In this talk, four research topics for photonic applications with metasurfaces and meta-devices will be performed and discussed: high efficiency anomalous beam deflector, highly dimensional holographic imaging, versatile polarization control and metadevices with active property.

The past few years have witnessed the discovery of photonic topological insulators, which transformed our views on propagation and scattering of electromagnetic waves. Here we show that judiciously designed all-dielectric photonic metamaterials and metasurfaces can exhibit a topological photonic state. The bianisotropy of the metamaterial is shown to result in emergence of a topological photonic band gap in the bulk and photonic states guided by edges and interfaces which appear to be one-way spin-polarized and immune to sharp bending. Experimental realizations of photonic topological metamaterials and metasurfaces for microwave and optical domains are used to test and confirm the topological properties.

In this project we propose and fabricate a hyperbolic metamaterials-based narrowband notch filter for the infrared regime with a center wavelength that remains fixed as the angle of incidence changes from 0 to 30 degrees for TM polarization. This novel device modifies a conventional Bragg reflector by including a middle resonance layer that opens up a narrow, highly transmissive band. To achieve angular independence, a subwavelength sized array of silver wires are inserted in a vertical orientation and permeate all 7 Si and SiO2 layers of the structure. In this work the theoretical underpinnings are explored using Maxwell-Garnett Theory, and simulated with 3D finite element full wave electromagnetic modeling software. Simulations demonstrate that the device is capable of up to 60% transmission at a fixed center wavelength for TM polarization in the infrared. The device is fabricated using typical microfabrication techniques. The silver nanowires are fabricated via DC electrodeposition. The angle and polarization dependent transmission, reflection and absorption of the device are experimentally measured, and scanning electron microscopy images of the structure are shown. Though the experimental validation of this device is performed for the infrared regime, scaling the structural sizes can extend the operating regime to higher and lower wavelengths. Whether used as a stand-alone filter, or integrated into a hyperspectral array, the angle-independent response of this filter has many uses in remote sensing applications.