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A new research field is emerging in which ensembles of molecules are collectively hybridised with light in a process known as strong coupling. This hybridisation leads to the formation of new states that are part light and part matter, states known as polaritons. Here we offer an entry point into the field of molecular strong coupling. We include an overview of the essential phenomena and an introduction to the conceptual framework – considerable use is made of simple classical physics models since they are helpful in developing an intuitive understanding. Open questions are identified and discussed, as well as some of the exciting experimental and theoretical challenges that lie ahead. [ABSTRACT FROM AUTHOR]

Examines the energy gaps in surface plasmon polaritons (SPP) which prohibit the propagation of surface modes. Arrangement used to image the dispersion curve of the SPP; Fabrication of photoresist gratings; Results on the width of the gap and the central frequency.

The paper reports measurements on the efficiency of coupling between a surface plasmon polariton mode and radiation using a periodic corrugated surface. For surface plasmon polaritons (SPPs) propagating parallel to the Bragg vector of the corrugation, coupling efficiencies of 70% were observed. The coupling efficiency was also measured for different SPP propagation directions relative to the corrugation and found to be high over a wide range of SPP propagation directions. These results are discussed in the context of emission from SPP-based light emitting devices. [ABSTRACT FROM AUTHOR]

Optical microcavities allow control over the interaction between light and matter, thus making them an important testing ground for basic optical physics. This review focuses on two of these interactions, spontaneous emission and energy transfer. Emphasis is placed on the underlying concepts, which are presented in the context of recent developments. Practical application of the microcavity concept to devices is now well underway and a discussion of these aspects forms an integral part of the review. This field is far from mature and though much has been accomplished, many questions in this area remain, some of which are identified and discussed. [ABSTRACT FROM AUTHOR]

We use a computational model to investigate the different routes by which power is lost by an optical emitter placed in a microcavity environment. We make a quantitative investigation of the 1/2n[sup 2] model used by many workers in evaluating the fraction of power radiated from athin film of emitting material. We show the limitations of the 1/2n[sup 2] model, emphasizing the important role of the orientation of the dipole moment of the emitters. Multi-layer systems, involving dielectric Bragg stack reflectors and metal mirrors, are compared for their efficiency in producing useful radiation. We consider both a standard Bragg reflector and the recently developed omni-directional Bragg stack. We show that metal mirrors, although lossy, may still be effective for producing useful radiation from microcavities. We focus our attention on parameters appropriate for organic microcavity light emitting diode structures. [ABSTRACT FROM AUTHOR]

By employing a combination of time-domain measurements and numerical calculations, we demonstrate that the semiconductor InSb supports a strongly confined surface plasmon (SP) in the terahertz frequency range. We show that these SPs can be used to enhance the light-matter interaction with dielectric layers above the semiconductor surface, thereby allowing us to detect the presence of polystyrene layers around 1000 times thinner than the free space wavelength of the terahertz light. Finally we discuss the viability of using semiconductor SPs for the purposes of terahertz sensing and spectroscopy. [ABSTRACT FROM AUTHOR]

We show that the emission of light from a dye layer through an adjacent thin silver film is maximal for a silver thickness of approximately 50 nm. This effect is explained as the result of competition between enhancement of the electric field at the metal surface due to the excitation of a surface plasmon-polariton mode, the amount of power coupled to the surface plasmon-polariton mode, and the attenuation of the field transmitted through the silver, all three of which vary with metal thickness. We indicate how these findings may be of relevance in the design of some surface plasmon-polariton-based fluorescence biosensing schemes. [ABSTRACT FROM AUTHOR]

We report the experimental observation of strong exciton–photon coupling in a planar microcavity composed of an organic semiconductor positioned between two metallic (silver) mirrors. Via transmission and reflectivity measurements, we observe a very large, room temperature Rabi splitting in excess of 300 meV. We show that the Rabi-splitting is enhanced in all-metal microcavities by a factor of more than 2 compared to an organic film positioned between a silver mirror and a dielectric mirror. This enhancement results from the significantly larger optical fields that are confined within all-metal microcavities. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A nanostructured surface in the form of a bi-grating is shown to efficiently couple surface plasmon polaritons to free-space radiation in the visible part of the spectrum. Coupling was achieved for all propagation directions of the surface mode and the efficiency found to be independent of the propagation direction, taking a mean value of 60% for the structure examined. The consequences of the findings for emissive devices that make use of surface plasmons are discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this article, we report experimental results on the control of spontaneous emission from sources embedded within metal-clad microcavities. The microcavity samples consist of an Eu[sup 3+] doped emissive monolayer embedded with a planar dielectric slab, bounded by a silver film on each side. We investigate the effect of both the cavity thickness and the location of the emissive monolayer within the cavity on the spontaneous emission rate of the emitters, observing both enhancement and inhibition. By varying the thickness of one of the silver films we also investigate the role of the reflectivity of the mirrors of the cavity on the control of spontaneous emission. In addition to the emission rate, results are presented on the spatial distribution of the emitted radiation. We find good agreement between our experimental results and those predicted by a classical theory over a large range microcavity structures. This agreement allows us to assess the contribution of the decay mediated by the electromagnetic modes of the cavity and the intrinsic nonradiative decay to the spontaneous emission rate. We then compare the ability of metal-clad and hybrid (one metal mirror and one distributed Bragg reflector) microcavity designs to optimize the efficiency of radiative emission. We show that enhancements, due to the increased confinement of the electromagnetic modes supported by the metal-clad microcavities, can be sufficient to overcome the loss associated with the absorption in the metal layers. We discuss the implication these results may have for device design. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A detailed comparison is made between the experimentally determined photonic band structure and the measured angle-dependent emission spectra of textured, metal-clad microcavities containing the light-emitting polymer MEH-PPV. Transmittivity measurements were made over a range of optical frequency and in-plane wavevector in order to obtain a detailed map of the dispersion of the waveguide modes supported by the textured cavities. Emission spectra were also recorded, for a large number of sample orientations, and are compared with the transmittivity maps. It is found that the band structure strongly influences the wavelength of the peaks in the emission spectra, and that the periodic texture leads to the generation of Bragg-scattered emission. The positions of these spectral peaks in both frequency and in-plane wavevector are found to agree very well with the positions of peak transmittivity of the cavities. The emission spectra also show clear evidence of the photonic band gaps formed by the periodic texture. The importance of these findings for light-emissive devices such as the light emitting diode is discussed. [ABSTRACT FROM AUTHOR]

Weshow that dye-doped polymers open an interesting route to controllinglight at the nanoscale. Just as for the much better known metal-basedplasmonic systems, propagating and localized modes are possible. Weshow that the attractive features offered by plasmonics, specificallyenhanced optical fields and subwavelength field confinement, are alsoavailable with these materials. They thus open a new opportunity innanophotonics in which fabrication and functionality might be achievedby harnessing molecular and supramolecular chemistry. [ABSTRACT FROM AUTHOR]

We present results of numerical simulations for structures comprised of metallo-dielectric layers in which the metal layers are perforated with non-diffracting arrays of subwavelength holes, structures that are similar to the 'fishnet' structures being studied as electromagnetic metamaterials. We find for visible frequencies that such structures exhibit a stop-band in transmittance across a broad frequency range, which arises through interactions between two distinctly different types of resonant mode. Using numerical (finite element) modelling to characterise the optical response, we identify strong coupling between Fabry-Perot resonant cavity modes within the multilayer structure and localised surface-plasmon resonances associated with the nanoholes. Our simulations show that the spectral position and width of the stop-band that occurs within the visible frequency range can be tuned by varying both the cavity spacing and the geometry of the nanohole array. [ABSTRACT FROM AUTHOR]

The Moderate Resolution Imaging Spectroradiometer (MODIS) protoflight model onboard the National Aeronautics and Space Administration's Earth Observing System Terra spacecraft has been in operation for over five years since its launch in December 1999. It makes measurements using 36 spectral bands with wavelengths from 0.41 to 14.5 μm. Bands 1–19 and 26 with wavelengths below 2.2 μm, the reflective solar bands (RSBs), collect daytime reflected solar radiance at three nadir spatial resolutions: 0.25 km (bands 1–2), 0.5 km (bands 3–7), and 1 km (bands 8–19 and 26). Bands 20–25 and 27–36, the thermal emissive bands, collect both daytime and nighttime thermal emissions, at 1-km nadir spatial resolution. The MODIS spectral characterization was performed prelaunch at the system level. One of the MODIS onboard calibrators, the Spectroradiometric Calibration Assembly (SRCA), was designed to perform on-orbit spectral characterization of the MODIS RSB. This paper provides a brief overview of MODIS prelaunch spectral characterization, but focuses primarily on the algorithms and results of using the SRCA for on-orbit spectral characterization. Discussions are provided on the RSB center wavelength measurements and their relative spectral response retrievals, comparisons of on-orbit results with those from prelaunch measurements, and the dependence of center wavelength shifts on instrument temperature. For Terra MODIS, the center wavelength shifts over the past five years are less than 0.5 nm for most RSBs, indicating excellent stability of the instrument's spectral characteristics. Similar spectral performance has also been obtained from the Aqua MODIS (launched in May 2002) SRCA measurements. [ABSTRACT FROM AUTHOR]

We show that the transmission of light through metallic hole arrays supported by a glass substrate can be tuned by depositing a controlled number of Langmuir–Blodgett layers on top of the hole array. Enhanced transmission is achieved when the number of overlayers is such that the surface plasmon-polariton modes on the two sides of the metal hole array have matched wavevectors. Dye molecules introduced into some of these overlayers allow us to explore the relationship between molecular fluorescence and the transmission properties of the structure, through measurement of the fluorescence lifetime of the molecules. We find there to be little change in the fluorescence lifetime between enhanced and non-enhanced transmission regimes and offer an explanation of our findings in terms of changes in the photonic mode density. [ABSTRACT FROM AUTHOR]

We used cavity quantum electrodynamic effects to determine the orientation of a species of organic dye molecule located in a microcavity environment. We used the Langmuir-Blodgett technique to fabricate well-controlled multilayer structures into which we incorporated dye molecules with well-defined layer positions. Comparing the results of fluorescence lifetime measurements and radiation patterns with theoretical calculations allowed us to determine both the orientation and the quantum efficiency of the dye molecules. [ABSTRACT FROM AUTHOR]

We report strong photoluminescence from a top-emitting organic light-emitting structure where emission takes place through a thin (55 nm) silver film. We show that this emission is mediated via coupled surface plasmon-polariton modes. Our results show that the addition of a dielectric grating to otherwise planar structures, such as surface-emitting organic light-emitting diodes, may offer a way to increase the external efficiency of top-emitting organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

We report results obtained from modeling the light outcoupling efficiency of top–emitting organic light-emitting diode (OLED) structures and compare them with results from conventional substrate-emitting structures. We investigate two types of emissive material, small molecule and conjugated polymers, and study three different cathode materials; aluminum, silver, and calcium. We show that top-emitting OLEDs may have outcoupling efficiencies comparable to their substrate-emitting counterparts, and that the choice of cathode material is critical to the optical performance of the device. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the demonstration of a compact, all-solid-state polymer laser system featuring a microchip laser as the pump source. The laser was configured as a surface-emitting, two-dimensional distributed feedback laser, based on the conjugated polymer poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene). Pulsed, band-edge lasing was observed at 636 nm above a threshold pump energy of 4 nJ. The laser exhibited an energy slope efficiency of 6.8%, with a maximum output energy of 1.12 nJ at a pump energy of 20.4 nJ. The output beam had an azimuthally polarized annular profile with a beam quality factor (M[SUP2]) of 2.2, close to the theoretical value of the lowest-order Laguerre-Gaussian and Bessel-Gaussian annular modes. We explain the origin of the azimuthal polarization as due to a coherent combination of the resonant fields supported by the two gratings. [ABSTRACT FROM AUTHOR]

We studied the role of the aperture depth on the enhanced transmission of light through subwavelength holes in free-standing Ag films by measuring the transmission properties of square arrays of cylindrical holes. Two regimes are found which give insight into the transmission mechanism and will be of importance for device applications. [ABSTRACT FROM AUTHOR]

We present the optical properties of a directly patterned light-emitting polymer. The patterned poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-paraphenylenevinylene film is fabricated using hot embossing lithography. The effect of the embossed microstructure on the light emitted from the polymer is examined by measuring the angle-dependent photoluminescence and its photonic band structure. The imposed grating modifies the emitted light by Bragg scattering into free space light that would otherwise be trapped as waveguide modes. This simple patterning technique may find application in improving the performance of light-emitting polymer devices. [ABSTRACT FROM AUTHOR]

We report the fabrication of widely tuneable (627–702 nm) optically pumped two-dimensional distributed feedback polymer lasers that utilize a red-emission fluorene copolymer as the active gain medium. The lasers exhibit efficient, low threshold operation and emit highly directional output beams as a result of the enhanced two-dimensional photonic confinement provided by the employed resonator. Their emission and operating characteristics are described in detail. We demonstrate that the very wide spectral range (Δλ>=75 nm) over which these lasers can be systematically tuned is in very good agreement with theoretical predictions based on a simple waveguide model. In addition, we show that the lasers have long operating lifetimes τ1/2>=2×107 pulses and we discuss the impact that degradation has on the laser output characteristics. [ABSTRACT FROM AUTHOR]

Electrical control over the energy exchange between exciton states mediated by cavity-polaritons at room temperature is demonstrated. A field-effect device, based on a monolayer of WS2, is built on the bottom metallic mirror of a tuneable Fabry–Pérot microcavity; on the top mirror, a monolayer of MoS2 is placed leaving a controllable gap of ∼1 μm between the top and bottom semiconductors. This device is specially designed for the multiple hybridization of microcavity modes with the two exciton species supported by WS2 and MoS2, allowing for polariton-mediated exciton energy exchange. It is further shown that the tuning of the free carrier density in the WS2 film through field-effect gating leads to strong modulation of the Rabi splitting that modifies the excitonic and photonic nature of exciton-polaritons. Electrical control of polaritonic devices may lead to technological applications using switchable quantum states. [ABSTRACT FROM AUTHOR]

The design and fabrication of a novel plasmonic cavity, intended to allow far-field recovery of signals arising from near field magneto-optical interactions, is presented. Finite element modeling is used to describe the interaction between a gold film, containing cross-shaped cavities, with a nearby magnetic under-layer. The modeling revealed strong electric field confinement near the center of the cross structure for certain optical wavelengths, which may be tuned by varying the length of the cross through a range that is compatible with available fabrication techniques. Furthermore, the magneto optical Kerr effect (MOKE) response of the composite structure can be enhanced with respect to that of the bare magnetic film. To confirm these findings, cavities were milled within gold films deposited upon a soluble film, allowing relocation to a ferromagnetic film using a float transfer technique. Cross cavity arrays were fabricated and characterized by optical transmission spectroscopy prior to floating, revealing resonances at optical wavelengths in good agreement with the finite element modeling. Following transfer to the magnetic film, circular test apertures within the gold film yielded clear magneto-optical signals even for diameters within the sub-wavelength regime. However, no magneto-optical signal was observed for the cross cavity arrays, since the FIB milling process was found to produce nanotube structures within the soluble under-layer that adhered to the gold. Further optimization of the fabrication process should allow recovery of magneto-optical signal from cross cavity structures. [ABSTRACT FROM AUTHOR]

We study THz pulses generated from plasmonic metal nanostructures under femtosecond illumination of near-IR light. We find two regimes of excitation, according to the order of the dependence of the THz fluence on the incident near-IR intensity: less then second order at low intensities, changing to approximately fourth order for higher intensities. These regimes are most likely associated with two THz generation mechanisms: optical rectification, and the ponderomotive acceleration of ejected electrons. These data provide evidence that both mechanisms can be at work in the same experiment. [ABSTRACT FROM AUTHOR]

A comparison is presented of a number of simulation techniques that are used to compute the scattering of electromagnetic radiation by metallic nanostructures. The simulation techniques considered here are Mie theory, the T-Matrix null-field method, the discrete-dipole approximation, the finite-element method and the finite-difference time-domain method. The suitability of each technique is compared in terms of the accuracy, computation time and the range of geometries to which it can be applied. Using each technique, we perform example calculations by simulating the optical response of an 80 nm diameter Au sphere in vacuum. Our main conclusions are summarised in tabulated form, so that the findings presented in this article may serve as a useful reference guide to those looking for suitable numerical tools to model the optical response of metallic nanostructures. [ABSTRACT FROM AUTHOR]

We present experimental results showing the variation in photoluminescence from an organic material emitted through a thin metal film as successive dielectric overlayers are added to the far side of the metal. The intensity of the emission from the structure is examined as the surface plasmon–polariton (SPP) modes associated with the two metal surfaces evolve with increasing overlayer thickness from individual to coupled SPP modes. The SPP modes are scattered to produce light by the addition to the metal film of wavelength-scale periodic microstructure. We show that the addition of a dielectric overlayer of an appropriate thickness to the metal film is accompanied by an increase in the intensity of the emission by a factor of 3 over a similar structure with no dielectric overlayer, and by a factor of 50 over a similar planar structure. We show that this increase in emission is mediated via coupled SPP modes. [ABSTRACT FROM AUTHOR]

We present experimental results showing electroluminescence from a dendrimer based organic light-emitting diode (OLED) mediated via surface plasmon polariton (SPP) modes. A combination of angle dependent electroluminescence, photoluminescence, and reflectance measurements is used to identify emission originating from the guided modes of the device. It is found that the SPP modes, which are usually nonradiative, are coupled to light by a wavelength scale periodic microstructure. It is demonstrated that the necessary microstructure can be readily fabricated by solvent-assisted micromoulding. Our results indicate that such an approach may offer a means to increase the efficiency of dendrimer based OLEDs. [ABSTRACT FROM AUTHOR]

We report the demonstration of a low-threshold, edge-emitting polymer distributed feedback laser based on a square lattice. The lattice constant was 268 nm, which corresponds to a lattice line spacing in the ΓM symmetry direction of the Brillouin zone of 189 nm. The latter was employed to provide feedback at 630 nm via a first order diffraction process. The device operated on two longitudinal modes, which were situated on the band-edge near the M symmetry point. The two modes had thresholds of 0.66 nJ and 1.2 nJ—significantly lower than comparable surface-emitting DFB lasers. Angle dependent photoluminescence experiments were performed to investigate the effect of the square lattice on the laser operation and the origin of the low threshold. [ABSTRACT FROM AUTHOR]

Split-ring resonators (SRRs) are a fundamental building block of many electromagnetic metamaterials. Typically the response of a metamaterial is assumed to be independent of interelement interactions in the material. We show that SRRs in close proximity to each other exhibit a rich coupling that involves both electric and magnetic interactions. We study experimentally and computationally the strength and nature of the coupling between two identical SRRs as a function of their separation and relative orientation. We characterize the electric and magnetic couplings and find that, when SRRs are close enough to be in each other's near field, the electric and magnetic couplings may either reinforce each other or act in opposition. At larger separations retardation effects become important. [ABSTRACT FROM AUTHOR]

The dispersion of optical modes in metallic microcavities is shown to be dramatically altered when wavelength-scale periodic texture is added to one of the cavity mirrors. We demonstrate that Bragg scattering of the cavity modes by such microstructure produces near-flat bands that remain significantly flat well away from the first Brillouin zone boundary. The electric fields associated with these modes are studied and are found to have field maxima that are enhanced over those pertaining to planar microcavities. The impact of this band structure upon emissive devices, especially in terms of the clear insensitivity to viewing angle, is discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]