Boundary effects in finite size plasmonic crystals: focusing and routing of plasmonic beams for optical communications

Plasmonic crystals, which consist of periodic arrangements of surface features at a metal-dielectric interface, allow the manipulation of optical information in the form of surface plasmon polaritons. Here we investigate the excitation and propagation of plasmonic beams in and around finite size plasmonic crystals at telecom wavelengths, highlighting the effects of the crystal boundary shape and illumination conditions. Significant differences in broad plasmonic beam generation by crystals of different shapes are demonstrated, while for narrow beams, the propagation from a crystal onto the smooth metal film is less sensitive to the crystal boundary shape. We show that by controlling the boundary shape, the size and the excitation beam parameters, directional control of propagating plasmonic modes and their behaviour such as angular beam splitting, focusing power and beam width can be efficiently achieved. This provides a promising route for robust and alignment-independent integration of plasmonic crystals with optical communication components.

Shaping plasmon beams via the controlled illumination of finite-size plasmonic crystals

Plasmonic crystals provide many passive and active optical functionalities, including enhanced sensing, optical nonlinearities, light extraction from LEDs and coupling to and from subwavelength waveguides. Here we study, both experimentally and numerically, the coherent control of SPP beam excitation in finite size plasmonic crystals under focussed illumination. The correct combination of the illuminating spot size, its position relative to the plasmonic crystal, wavelength and polarisation enables the efficient shaping and directionality of SPP beam launching. We show that under strongly focussed illumination, the illuminated part of the crystal acts as an antenna, launching surface plasmon waves which are subsequently filtered by the surrounding periodic lattice. Changing the illumination conditions provides rich opportunities to engineer the SPP emission pattern. This offers an alternative technique to actively modulate and control plasmonic signals, either via micro- and nano-electromechanical switches or with electro- and all-optical beam steering which have direct implications for the development of new integrated nanophotonic devices, such as plasmonic couplers and switches and on-chip signal demultiplexing. This approach can be generalised to all kinds of surface waves, either for the coupling and discrimination of light in planar dielectric waveguides or the generation and control of non-diffractive SPP beams.

Manipulating polarization of light with ultrathin epsilon-near-zero metamaterials

One of the basic functionalities of photonic devices is the ability to manipulate the polarization state of light. Polarization components are usually implemented using the retardation effect in natural birefringent crystals and, thus, have a bulky design. Here, we have demonstrated the polarization manipulation of light by employing a thin subwavelength slab of metamaterial with an extremely anisotropic effective permittivity tensor. Polarization properties of light incident on the metamaterial in the regime of hyperbolic, epsilon-near-zero, and conventional elliptic dispersions were compared. We have shown that both reflection from and transmission through λ/20 thick slab of the metamaterial may provide nearly complete linear-to-circular polarization conversion or 90° linear polarization rotation, not achievable with natural materials. Using ellipsometric measurements, we experimentally studied the polarization conversion properties of the metamaterial slab made of the plasmonic nanorod arrays in different dispersion regimes. We have also suggested all-optical ultrafast control of reflected or transmitted light polarization by employing metal nonlinearities.

Broadband and broadangle SPP antennas based on plasmonic crystals with linear chirp

Plasmonic technology relies on the coupling of light to surface electromagnetic modes on smooth or structured metal surfaces. While some applications utilise the resonant nature of surface polaritons, others require broadband characteristics. We demonstrate unidirectional and broadband plasmonic antennas with large acceptance angles based on chirped plasmonic gratings. Near-field optical measurements have been used to visualise the excitation of surface plasmon polaritons by such aperiodic structures. These weakly aperiodic plasmonic crystals allow the formation of a trapped rainbow-type effect in a two-dimensional geometry as surface polaritons of different frequencies are coherently excited in different locations over the plasmonic structure. Both the crystal's finite size and the finite lifetime of plasmonic states are crucial for the generation of broadband surface plasmon polaritons. This approach presents new opportunities for building unidirectional, broadband and broad-angle plasmonic couplers for sensing purposes, information processing, photovoltaic applications and shaping and manipulating ultrashort optical pulses.

Hyperspectral imaging with scanning near-field optical microscopy: applications in plasmonics

We present the realisation of near-field spectroscopic measurements with fibre-tip-based scanning near-field microscopy. It allows the simultaneous acquisition of near-field images in a broad spectral range (400 nm to 1000 nm), thus recovering local spectroscopic information. This technique is essential in order to understand the resonant interaction of light with nanostructured material as the far-field and near-field spectral response can differ significantly, e.g., in the case of plasmonic nanostructures. Several example applications of hyperspectral near-field imaging are given for visualisation of Bloch modes in plasmonic crystals and plasmon-assisted transmission through a slit.

Amplified spontaneous emission of surface plasmon polaritons and limitations on the increase of their propagation length

Amplified spontaneous emission of surface plasmon polaritons (SPPs) at the interface of a resonant gain medium has been observed. The amplification is accompanied by significant spectral narrowing and limits the gain available for compensation of SPP propagation losses. The effect is similar to the deteriorating influence of amplified spontaneous emission in laser resonators.

Social health outcomes following thermal injuries: a retrospective matched cohort study

INTRODUCTION

Over 50% of children admitted with burns are aged under 3 years. US studies suggest that up to 26% of childhood burns are non-accidental, although UK reports are lower (1-16%).

OBJECTIVES

To determine the social health outcomes of burned children as regards the number of children abused, neglected or "in need" before the age of 6 years compared with matched controls.

METHODS

A retrospective matched cohort study. 145 children aged under 3 years admitted for burns in 1994-1997 were matched with controls for sex, age and enumeration district and followed up until 2003. Electronic routine databases provided study data on local authority care episodes and Social Services referrals by age 6 years.

RESULTS

89.0% of cases had accidental burns and four cases (2.8%) had non-accidental burns. No case was attributed to neglect. By their sixth birthday cases were statistically more likely to have been referred to Social Services with 14 (9.7%) of the burned children having been abused or neglected versus two (1.4%) controls (95% CI 0.030 to 0.13, p = 0.004). Forty six (32%) cases versus 26 (18%) controls were defined as "in need" (95% CI 0.047 to 0.23, p = 0.006).

CONCLUSION

Although most burns were deemed accidental, 2.8% were categorised as non-accidental at presentation. Almost a third of the burned children went on to be "in need". Children with a burn appear to be at higher risk of further abuse or neglect compared with controls. A burn therefore could be a surrogate marker indicating need for closer supervision and follow-up by professionals.

Guided plasmonic modes in nanorod assemblies: strong electromagnetic coupling regime

We demonstrate that the coupling between plasmonic modes of oriented metallic nanorods results in the formation of an extended (guided) plasmonic mode of the nanorod array. The electromagnetic field distribution associated to this mode is found to be concentrated between the nanorods within the assembly and propagates normally to the nanorod long axes, similar to a photonic mode waveguided by an anisotropic slab. This collective plasmonic mode determines the optical properties of nanorod assemblies and can be tuned in a wide spectral range by changing the nanorod array geometry. This geometry represents a unique opportunity for light guiding applications and manipulation at the nanoscale as well as sensing applications and development of molecular plasmonic devices.

Near-field imaging of ultrathin magnetic films with in-plane magnetization

A new approach to near-field magneto-optical imaging was developed capable of visualization of in-plane magnetization of ultrathin magnetic structures. The approach relies on the magneto-optical effect specific for thin magnetic layers and employs near-field transmission measurements of longitudinal and/or transverse magneto-optical effect arising from the presence of thin film interfaces. The near-field magneto-optical contrast of in-plane domain structure of ultrathin Co film has been demonstrated in different polarization configurations.

Predictors of post-traumatic stress symptoms in Oklahoma City: exposure, social support, peri-traumatic responses

Eighty-five adults seeking mental health assistance six months after the Oklahoma City bombing were assessed to determine which of three groups of variables (exposure, peri-traumatic responses, and social support) predicted development of post-traumatic stress disorder (PTSD) symptoms. Variables most highly associated with subsequent PTSD symptoms included having been injured (among exposure variables), feeling nervous or afraid (peri-traumatic responses), and responding that counseling helped (support variables). Combining primary predictors in the three areas, PTSD symptoms were more likely to occur in those reporting counseling to help and those feeling nervous or afraid at the time of the bombing. Implications of these findings are discussed for behavioral health administrators and clinicians planning service delivery to groups of victims seeking mental health intervention after terrorist attacks and other disasters.

Traumatic reactions as predictors of posttraumatic stress six months after the Oklahoma City bombing

OBJECTIVE

This study attempted to identify remembered reactions of Oklahoma City residents at the time of the April 1995 terrorist bombing that predicted later development of posttraumatic stress symptoms.

METHODS

Eighty-six adults who sought help for distress related to the bombing six months after it occurred completed a survey about demographic characteristics, level of exposure to the event, symptoms of grief, retrospective reports of reactions at the time of the trauma, current posttraumatic stress symptoms, and coping strategies. To identify immediate bombing reactions predictive of later distress, retrospective reports of reactions to the trauma were correlated with current posttraumatic stress symptoms. Multiple regression analysis was used to determine which reactions predicted the emergence of posttraumatic stress symptoms.

RESULTS

Reactions of being nervous and being upset by how other people acted when the bombing occurred accounted for about one-third of the total variation in posttraumatic stress symptom scores and thus were major predictors of posttraumatic stress.

CONCLUSIONS

These results differ from those of other studies in which peritraumatic dissociation, or dissociation at the time of the event, was more predictive than anxiety for developing later distress. The results suggest that persons who experience significant anxiety at the time of the traumatic event may continue to experience distress. Those who are overly concerned about others' actions may be showing diminished interpersonal trust, evidence of terrorism's ability to erode social harmony.

Patterns of scald injuries

OBJECTIVES

To describe common patterns of bath water scald injuries in children, to examine differences between accidental and non-accidental bath water scalds in children, and to examine potential for prevention.

DESIGN

A two year six month retrospective analysis of admissions to a specialist burns unit.

SETTING

The Burns Unit, St Lawrence Hospital, Chepstow serving children from south and west Wales.

SUBJECTS

Sixty eight children attending the Burns Unit for treatment of bath related scald injuries.

RESULTS

Bath scalds in children under 5 years of age was the cause of 14.7 per 100,000 children being admitted to the specialist burns unit in a year. The majority of the children were injured by falling in the bath but the tap was turned on by seven children themselves and by 10 siblings. Six children put hands in the hot water and two children were accidentally put into bath water that was too hot and were quickly withdrawn. Four children suffered probably non-accidental immersion scald injuries from hot water. They were characterised by a clear tide mark, a story that did not fit the injuries, associated injuries, and by symmetrical lesions. Accidental scalds were irregular geographical injuries and were asymmetrical.

CONCLUSIONS

Bath scalds are a significant problem in children under 5 years. Their prevention should be part of an injury control programme on a local and national level. The best way to achieve this would be by reducing the temperature in domestic hot water tanks. The recognition of non-accidental bath scalds can be assisted by the pointers outlined and should be done in a multidisciplinary way with plastic surgeons, paediatricians, and social workers working together.

Meningococcal infections in Bolton, 1971-74

Between December 1970, and the end of June, 1974, there were 82 cases of meningococcal infection, including 14 deaths, in the metropolitan borough of Bolton. This outbreak, caused by a sulphonamide-sensitive group-B strain, was characterised by a high attack-rate in young children, reaching a peak of 184 per 100,000 per year in the 6-11-month age-group. All the deaths were in children under 3 years of age. Nasopharyngeal carriage of the epidemic strain was found in 34% of close family contacts investigated before receiving sulphonamide prophylaxis.

Beclomethasone dipropionate aerosol in childhood asthma

Twenty-five patients with severe childhood asthma were treated with beclomethasone dipropionate. 21 of these children were receiving oral corticosteroid therapy in addition to disodium cromoglycate. Of the total treated, 21 children improved or maintained their asthma status on this treatment over an average period of 4 months, and were able to reduce and stop their regular oral corticosteroid dosage, but 4 children had to revert to their original therapy. No systemic or local toxic effects were experienced by any of the children. Beclomethasone dipropionate appears to be an effective drug in the treatment of severe childhood asthma in those patients who need corticosteroid therapy in addition to disodium cromoglycate.