Daniel O'Connor

Near-Field Interference for the Unidirectional Excitation of Electromagnetic Guided Modes

Controlling Light Propagation Surface plasmons are light-induced collective electronic excitations in a metal that offer the possibility of manufacturing optoelectronic devices at nanometer scale. Before such shrinking can be achieved, the propagation direction and lifetime of the plasmonic excitations have to be controlled (see the Perspective by Miroshnichenko and Kivshar). Rodríguez-Fortuño et al. (p. 328) show how this is done using polarized light. Alternatively, using an array of metallic nanoantennae (in this case, slits) patterned into a thin gold film, Lin et al. (p. 331) present a further improvement on current plasmonic coupling schemes that has the potential to encode information contained in both the intensity and polarization of light. Near-field interference can be used to control the directional propagation of electromagnetic excitations. [Also see Perspective by Miroshnichenko and Kivshar] Wave interference is a fundamental manifestation of the superposition principle with numerous applications. Although in conventional optics, interference occurs between waves undergoing different phase advances during propagation, we show that the vectorial structure of the near field of an emitter is essential for controlling its radiation as it interferes with itself on interaction with a mediating object. We demonstrate that the near-field interference of a circularly polarized dipole results in the unidirectional excitation of guided electromagnetic modes in the near field, with no preferred far-field radiation direction. By mimicking the dipole with a single illuminated slit in a gold film, we measured unidirectional surface-plasmon excitation in a spatially symmetric structure. The surface wave direction is switchable with the polarization.

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.

Spin–orbit coupling in surface plasmon scattering by nanostructures

The spin Hall effect leads to the separation of electrons with opposite spins in different directions perpendicular to the electric current flow because of interaction between spin and orbital angular momenta. Similarly, photons with opposite spins (different handedness of circular light polarization) may take different trajectories when interacting with metasurfaces that break spatial inversion symmetry or when the inversion symmetry is broken by the radiation of a dipole near an interface. Here we demonstrate a reciprocal effect of spin-orbit coupling when the direction of propagation of a surface plasmon wave, which intrinsically has unusual transverse spin, determines a scattering direction of spin-carrying photons. This spin-orbit coupling effect is an optical analogue of the spin injection in solid-state spintronic devices (inverse spin Hall effect) and may be important for optical information processing, quantum optical technology and topological surface metrology.

Low-temperature plasmonics of metallic nanostructures.

The requirements for spatial and temporal manipulation of electromagnetic fields on the nanoscale have recently resulted in an ever-increasing use of plasmonics for achieving various functionalities with superior performance to those available from conventional photonics. For these applications, ohmic losses resulting from free-electron scattering in the metal is one major limitation for the performance of plasmonic structures. In the low-frequency regime, ohmic losses can be reduced at low temperatures. In this work, we study the effect of temperature on the optical response of different plasmonic nanostructures and show that the extinction of a plasmonic nanorod metamaterial can be efficiently controlled with temperature with transmission changes by nearly a factor of 10 between room and liquid nitrogen temperatures, while temperature effects in plasmonic crystals are relatively weak (transmission changes only up to 20%). Because of the different nature of the plasmonic interactions in these types of plasmonic nanostructures, drastically differing responses (increased or decreased extinction) to temperature change were observed despite identical variations of the metals permittivity.

Data storage: The third plasmonic revolution

Combining nanostructured magnetic media with nanoplasmonic antennas has propelled commercially viable data-storage densities beyond one terabit per square inch.

Fabrication and optical properties of gold nanotube arrays

Arrays of gold nanotubes with polypyrrole cores were grown on glass substrates by electrodeposition into thin film porous alumina templates. Measurements of optical transmission revealed strong extinction peaks related to plasmonic resonances, which were sensitive to the polarization state and angle of incidence. On prolonging the electrodeposition of gold, the polypyrrole core became fully encapsulated and this had a dramatic effect on the optical properties of the arrays, which was rationalized by finite element simulation of the local field intensities resulting from plasmon excitation.

Longitudinal Cardiorespiratory Fitness Algorithms for Clinical Settings

BACKGROUND Non-exercise algorithms are cost-effective methods to estimate cardiorespiratory fitness (CRF) in healthcare settings. The limitation of current non-exercise models is that they were developed with cross-sectional data. PURPOSE To extend the non-exercise research by developing algorithms for men and women using longitudinal data on indicators available in healthcare settings. METHODS The sample included 1325 women (aged 20-78 years) and 10,040 men (aged 20-86 years) who completed two to 21 maximal treadmill tests between 1977 and 2005. The data were analyzed in 2011 and 2012. The dependent variable was CRF measured by treadmill test. The independent variables were age; body composition (percentage fat or BMI); waist circumference; self-reported physical activity; resting heart rate; and smoking behavior. RESULTS Linear mixed-models regression showed that all variables were independently related to CRF. There was a positive association between CRF and physical activity. Higher levels of body composition were linked to lower CRF. High resting heart rate and smoking resulted in lower estimates of CRF. The error estimates of the percentage fat algorithms were as follows: women, 1.41 METs (95% CI=1.35, 1.47); and men, METs 1.54 (95% CI=1.51, 1.55). The BMI models were somewhat less accurate: women, METs 1.51 (95% CI=1.45, 1.58); and men, 1.66 METs (95% CI=1.63, 1.68). CONCLUSIONS These results showed that the CRF of women and men can be estimated from easily obtained health indicators. The longitudinal non-exercise algorithms provide models to accurately estimate CRF changes associated with aging and provide cost-effective algorithms to track CRF over time with health indicators available in healthcare settings.

Effects of cardiorespiratory fitness on aging: glucose trajectory in a cohort of healthy men

PURPOSE We modeled the age-related trajectory of glucose and determined whether cardiorespiratory fitness altered the trajectory in a cohort of men from the Aerobics Center Longitudinal Study. METHODS A total of 10,092 men free of diagnosed diabetes, cardiovascular disease, and cancer, ages 20 to 90 years, completed from 2 to 21 health examinations between 1977 and 2005. Cardiorespiratory fitness was measured by a maximal treadmill exercise test and normalized for age. The covariates included waist circumference, hypertension, elevated cholesterol, smoking behavior, and physical activity. RESULTS Linear mixed models regression analysis showed that fasting glucose increased at a linear rate with aging. Glucose increased at a yearly rate of 0.17 mg/dL (95% confidence interval: 0.16-0.19). Fitness had little influence on the aging glucose trajectory below age 35, but significantly influenced the trend after age 35 (P for interaction < .001). The aging-related glucose increases in low-fitness men (0.25 mg/dL per year) was greater than average-fitness (0.15 mg/dL per year) and high-fitness (0.13 mg/dL per year) men. CONCLUSIONS The aging-related fasting glucose increases in low-fitness men was nearly double that of high-fitness men. Our results may suggest that it is possible to delay the age-related glucose impairment through increasing ones fitness level.

Home Availability and the Impact of Weekly Stressful Events Are Associated with Fruit and Vegetable Intake among African American and Hispanic/Latina Women

Background. Mediating and moderating variables may interfere with the association between neighborhood availability of grocery stores (NAG) and supermarkets (NAS) and fruit and vegetable (FV) intake. Objective. The purpose of this study was to test mediation of home availability of FV (HAFV) and moderation of impact of weekly stressful events (IWSE) on the association between NAG and NAS with FV consumption among African American (AA) and Hispanic/Latina (HL) women. Methods. Three hundred nine AA and HL, 25–60 year old women in the Health Is Power (HIP) randomized controlled trial completed validated measures of HAFV, IWSE, and FV intake at baseline. Trained field assessors coded NAG and NAS. Institutional Review Board approval was obtained. Results. NAG and NAS were not associated with FV intake or HAFV, so HAFV was not a mediator. HAFV (std. Beta = .29, P < 0.001) and IWSE (std. Beta = .17; P < 0.05) were related to FV intake (R2 = 0.17; P < 0.001), but IWSE was not a moderator. Conclusion. Increasing HAFV and decreasing the IWSE should increase FV consumption. The extent to which the neighborhood environment is related to the home food environment and diet, and the mechanisms for the association between IWSE and diet should be examined in future research.

Integrated plasmonic circuitry on a vertical-cavity surface-emitting semiconductor laser platform

Integrated plasmonic sources and detectors are imperative in the practical development of plasmonic circuitry for bio- and chemical sensing, nanoscale optical information processing, as well as transducers for high-density optical data storage. Here we show that vertical-cavity surface-emitting lasers (VCSELs) can be employed as an on-chip, electrically pumped source or detector of plasmonic signals, when operated in forward or reverse bias, respectively. To this end, we experimentally demonstrate surface plasmon polariton excitation, waveguiding, frequency conversion and detection on a VCSEL-based plasmonic platform. The coupling efficiency of the VCSEL emission to waveguided surface plasmon polariton modes has been optimized using asymmetric plasmonic nanostructures. The plasmonic VCSEL platform validated here is a viable solution for practical realizations of plasmonic functionalities for various applications, such as those requiring sub-wavelength field confinement, refractive index sensitivity or optical near-field transduction with electrically driven sources, thus enabling the realization of on-chip optical communication and lab-on-a-chip devices.