Reevaluation of radiation reaction and consequences for light-matter interactions at the nanoscale.

In the context of electromagnetism and nonlinear optical interactions, damping is generally introduced as a phenomenological, viscous term that dissipates energy, proportional to the temporal derivative of the polarization. Here, we follow the radiation reaction method presented in [Phys. Lett. A157, 217 (1991)], which applies to non-relativistic electrons of finite size, to introduce an explicit reaction force in the Newtonian equation of motion, and derive a hydrodynamic equation that offers new insight on the influence of damping in generic plasmas, metal-based and/or dielectric structures. In these settings, we find new damping-dependent linear and nonlinear source terms that suggest the damping coefficient is proportional to the local charge density and nonlocal contributions that stem from the spatial derivative of the magnetic field. We discuss the conditions that could modify both linear and nonlinear electromagnetic responses.

Impedance matched thin metamaterials make metals absorbing.

Metals are generally considered good reflectors over the entire electromagnetic spectrum up to their plasma frequency. Here we demonstrate an approach to tailor their absorbing characteristics based on the effective metamaterial properties of thin, periodic metallo-dielectric multilayers by exploiting a broadband, inherently non-resonant, surface impedance matching mechanism. Based on this mechanism, we design, fabricate and test omnidirectional, thin (<1 micron), polarization independent, extremely efficient absorbers (in principle being capable to reach A > 99%) over a frequency range spanning from the UV to the IR. Our approach opens new venues to design cost effective materials for many applications such as thermo-photovoltaic energy conversion devices, light harvesting for solar cells, flat panel display, infrared detectors, stray light reduction, stealth and others.

Thermal emission from a metamaterial wire medium slab.

We investigate thermal emission from a metamaterial wire medium embedded in a dielectric host and highlight two different regimes for efficient emission, respectively characterized by broadband emission near the effective plasma frequency of the metamaterial, and by narrow-band resonant emission at the band-edge in the Bragg scattering regime. We discuss how to control the spectral position and relative strength of these two emission mechanisms by varying the geometrical parameters of the proposed metamaterial and its temperature.

Broadband metamaterial for nonresonant matching of acoustic waves.

Unity transmittance at an interface between bulk media is quite common for polarized electromagnetic waves incident at the Brewster angle, but it is rarely observed for sound waves at any angle of incidence. In the following, we theoretically and experimentally demonstrate an acoustic metamaterial possessing a Brewster-like angle that is completely transparent to sound waves over an ultra-broadband frequency range with >100% bandwidth. The metamaterial, consisting of a hard metal with subwavelength apertures, provides a surface impedance matching mechanism that can be arbitrarily tailored to specific media. The nonresonant nature of the impedance matching effectively decouples the front and back surfaces of the metamaterial allowing one to independently tailor the acoustic impedance at each interface. On the contrary, traditional methods for acoustic impedance matching, for example in medical imaging, rely on resonant tunneling through a thin antireflection layer, which is inherently narrowband and angle specific.

Oesophageal cancer treatment in a tertiary referral hospital evaluated by indicators for quality of care.

BACKGROUND: Studies on quality of care for oesophageal cancer patients usually include only traditional outcome parameters. The aim of the study was to address quality of care in a broader perspective. METHODS: Between 2003 and 2008, 821 oesophageal cancer patients were referred to our institute. Indicators to measure quality of care (i.e., process and outcome measures) were defined and comparisons between two time periods were made. RESULTS: 335 patients came for a second opinion only, 382 patients received palliative treatment and 104 (13%) patients underwent potentially curative treatment. The median time between the first hospital visit and start of treatment decreased from 24 days in period I to 18 days in period II (P = 0.03). Of patients who underwent potentially curative treatment, 81% in period I and 86% in period II were discussed during a weekly multidisciplinary meeting (P = 0.54). Compliance with the national guideline was comparable in both periods (84% vs. 80%, P = 0.27). There were non-significant improvements in completion of chemoradiation (85% vs. 91%), postoperative complication rates (57% vs. 33%) and 3-year survival (40% vs. 46%). CONCLUSION: By evaluating different dimensions of health care quality, we have identified which steps in the multidisciplinary care path need more attention in order to raise the whole level of care. Efforts for improvement should focus primarily on process measures rather than on outcome measures for which high-quality standards are already met.

All-optical switching at the Fano resonances in subwavelength gratings with very narrow slits.

We theoretically discuss all-optical switching at the Fano resonances of subwavelength gratings made of a chalcogenide glass (As(2)S(3)). Particular attention is devoted to the case in which the grating possesses extremely narrow slits (channels ranging from a∼10 nm to a∼40 nm). The remarkable local field enhancement available in these situations conspires to yield low-threshold switching intensities (~50 MW/cm(2)) at telecommunication wavelengths for extremely thin (d∼200 nm) gratings when a realistic value of the As(2)S(3) cubic nonlinearity is used.

Transmission function properties for multi-layered structures: application to super-resolution.

We discuss the properties of the transmission function in the k-space for a generic multi-layered structure. In particular we analytically demonstrate that a transmission greater than one in the evanescent spectrum (amplification of the evanescent modes) can be directly linked to the guided modes supported by the structure. Moreover we show that the slope of the phase of the transmission function in the propagating spectrum is inversely proportional to the ability of the structure to compensate the diffraction of the propagating modes. We apply these findings to discuss several examples where super-resolution is achieved thanks to the simultaneous availability of the amplification of the evanescent modes and the diffraction compensation of the propagating modes.

TE and TM guided modes in an air waveguide with negative-index-material cladding.

We numerically demonstrate that a planar waveguide in which the inner layer is a gas with refractive index n0 = 1, sandwiched between two identical semi-infinite layers of a negative index material, can support both transverse electric and transverse magnetic guided modes with low losses. Recent developments in the design of metamaterials with an effective negative index suggest that this waveguide could operate in the infrared region of the spectrum.

Switching intense laser pulses guided by Kerr-effect-modified modes of a hollow-core photonic-crystal fiber.

A Kerr-nonlinearity-induced profile of the refractive index in the hollow core of a photonic-crystal fiber (PCF) changes the spectrum of propagation constants of air-guided modes, effectively shifting the passbands in fiber transmission, controlled by the photonic band gaps (PBGs) of the cladding. This effect is shown to allow the creation of fiber switches for high-intensity laser pulses. The Kerr-nonlinearity control of air-guided modes in PCFs and the performance of a PCF switch are quantified by solving the propagation equation for the slowly varying envelope of a laser pulse guided in Kerr-effect-modified PCF modes. The spatial dynamics of the light field in a PBG waveguide switch is analyzed with the use of the slowly varying envelope approximation, demonstrating high contrasts of optical switching with PBG waveguides and hollow PCFs.

Density of modes and tunneling times in finite one-dimensional photonic crystals: a comprehensive analysis.

We present a unified treatment of density of modes and tunneling times in finite, one-dimensional photonic crystals. We exploit connections and differences between the various approaches used to calculate the density of modes, which include the Green function, the Wigner phase time, and the electromagnetic energy density, and conclude that the Green function is always the correct path to the true density of modes. We also find that for an arbitrary structure the density of modes can always be found as the ratio between the power emitted by a source located inside the structure and the power emitted by the same source in free space, regardless of absorption or dispersion.

Slowing light in chi2 photonic crystals.

A study of parametric nonlinear frequency down-conversion in photonic crystals reveals that under suitable conditions the probe field can be slowed down to approximately 11 m/s. The effect arises as a result of the simultaneous availability of global phase-matching conditions, field localization, and gain experienced by the probe beam. Together, these effects conspire to yield tunneling velocities previously reported only for coherently resonant interactions, i.e., electromagnetic induced transparency, in Bose-Einstein condensates, hot atomic gases, and doped crystals.

Quasinormal-mode description of waves in one-dimensional photonic crystals.

Quasinormal-mode treatment is extended to the description of scalar field behavior in one-dimensional photonic crystals. A one-dimensional photonic crystal is a particular configuration of an open cavity, where discontinuities of the refractive index give rise to field confinement. This paper presents, for a one-dimensional photonic crystal, a discussion about the completeness of the quasinormal-mode representation and, moreover, a discussion on the complex eigenfrequencies, as well as the corresponding field distribution. The concept of density of modes is also discussed in terms of quasinormal modes.

Dynamics of counterpropagating pulses in photonic crystals: enhancement and suppression of stimulated emission processes.

Using numerical methods, we study the propagation of counterpropagating pulses in finite photonic crystals. We show that linear interference and localization effects combine to either enhance or suppress stimulated emission processes, depending on the initial phase difference between the input pulses. We consider the example of second harmonic generation, where we find a maximum contrast of three orders of magnitude in nonlinear conversion efficiency as a function of the input phase difference between incident pulses. We interpret these results by viewing the photonic crystal as an open cavity, with a field-dependent, electromagnetic density of modes sensitive to initial and boundary conditions.

Transit time of chirped pulses through one-dimensional, nonabsorbing barriers.

Experiments show that the transit times of chirped, narrow-band pulses that move across nonabsorbing, one-dimensional barriers are modified dramatically by the interplay between the chirp and the transmission function of the sample. In an experiment we monitored 0.9-ns chirped, nearly Gaussian pulses as they traversed a 450-mum GaAs etalon. At certain wavelengths pulse transit times can be superluminal or even negative. To explain these phenomena we have proposed a generalization of the transit time for chirped pulses that is still meaningful even when the transit times are superluminal or negative. Our predictions agree well with the experimental results.

Simultaneously phase-matched enhanced second and third harmonic generation.

Second and third harmonic generation via a chi((2)) three-wave mixing process can occur with high conversion efficiency in a one-dimensional photonic band gap structure. We find that it is possible to simultaneously achieve enhancement and exact phase-matching conditions of second harmonic and sum frequency generation, omega+2 omega-->3 omega. It is also remarkable that high conversion efficiencies persist under tuning conditions that correspond to a phase mismatch. While these conditions are quite unusual and cannot be achieved in any known bulk material, we show that they can be easily obtained in finite layered structures by using and balancing an interplay between material dispersion and the geometrical dispersion introduced by the structure.

Photonic band edge effects in finite structures and applications to chi 2 interactions.

Using the concept of an effective medium, we derive coupled mode equations for nonlinear quadratic interactions in photonic band gap structures of finite length. The resulting equations reveal the essential roles played by the density of modes and effective phase matching conditions necessary for the strong enhancement of the nonlinear response. Our predictions find confirmation in an experimental demonstration of significant enhancement of second harmonic generation near the photonic band edge. The measured conversion efficiency is in good agreement with the conversion efficiency predicted by the effective-medium model.

Group velocity, energy velocity, and superluminal propagation in finite photonic band-gap structures.

We have analyzed the notions of group velocity V(g) and energy velocity V(E) for light pulses propagating inside one-dimensional photonic band gap structures of finite length. We find that the two velocities are related through the transmission coefficient t as V(E)=/t/(2)V(g). It follows that V(E)=V(g) only when the transmittance is unity (/t/(2)=1). This is due to the effective dispersive properties of finite layered structures, and it allows us to better understand a wide range of phenomena, such as superluminal pulse propagation. In fact, placing the requirement that the energy velocity should remain subluminal leads directly to the condition V(g)

Essential thrombocythaemia as cause of myocardial infarction.

Abnormalities in the number and function of platelets may contribute to thromboembolic complications in patients with essential thrombocythaemia (ET). Rarely this can lead to an acute myocardial ischaemic syndrome. We describe a young patient with a myocardial infarction, in whom ET was found as the probable cause. We discuss the clinical presentation of ET and the therapeutic possibilities.

Enhancement of chi((2)) cascading processes in one-dimensional photonic bandgap structures.

We theoretically analyze the nonlinear phase shifts induced by cascaded chi((2)):chi((2)) processes in one-dimensional photonic bandgap structures. We find that the enhancement of the density of modes near the band edge, coupled with a suitable choice of relative phase mismatch, leads to a remarkable new effect: The relative phase shift of the fundamental field on transmission can be of the order of pi over a distance of 7mum , with input intensities of the order of only 10 MW/cm(2).

Dispersive properties of finite, one-dimensional photonic band gap structures: applications to nonlinear quadratic interactions.

We discuss the linear dispersive properties of finite one-dimensional photonic band-gap structures. We introduce the concept of a complex effective index for structures of finite length, derived from a generalized dispersion equation that identically satisfies the Kramers-Kronig relations. We then address the conditions necessary for optimal, phase-matched, resonant second harmonic generation. The combination of enhanced density of modes, field localization, and exact phase matching near the band edge conspire to yield conversion efficiencies orders of magnitude higher than quasi-phase-matched structures of similar lengths. We also discuss an unusual and interesting effect: counterpropagating waves can simultaneously travel with different phase velocities, pointing to the existence of two dispersion relations for structures of finite length.