Limitations of effective medium models for tissue phantoms in the THz frequency range.

The absorption of terahertz (THz) radiation by water molecules facilitates its application to several biomedical applications such as cancer detection. Therefore, it is critical for the THz technologies to be characterised with water content in a sample. In this paper, we analyse gelatine phantoms in the THz frequency range, with continuously varying hydration levels as they dry over time.

Rapid terahertz beam profiling and antenna characterization with phase-shifting holography.

In this paper we investigate the application of phase-shifting digital holography for the real-time characterization of electromagnetic sources in the THz frequency range. We use an off-the-shelf terahertz detector array composed of power-sensitive pixels, over an area of , to record intensity interferograms cast between the coherent radiation emitted from a reference source and an unknown antenna under test. This approach parallelizes the acquisition process with respect to conventional near-field point scanning methods, reducing the measurement time by orders of magnitude.

Frequency-Specific Effects of Noninvasive Median Nerve Stimulation on Gastric Slow Wave Activity in Humans.

Objectives: The present study explored the effects of different frequencies of noninvasive median nerve stimulation (nMNS) on two autonomic responses: gastric slow waves under water-loading condition and heart rate variability (HRV). To the best of our knowledge, this is the first study to document the effects of different frequencies of nMNS on gastric slow waves (GSW) in humans under 5-minute water-loading condition.

Materials And Methods: Twenty healthy adult participants were fitted with a noninvasive body-surface gastric mapping, electrocardiogram (ECG), and a transcutaneous electrical nerve stimulation device and administered with four different nMNS frequencies (placebo-0 Hz, 40 Hz, 120 Hz, and 200 Hz) on four separate counterbalanced days.

Real-time millimeter wave holography with an arrayed detector.

Millimeter and terahertz wave imaging has emerged as a powerful tool for applications such as security screening, biomedical imaging, and material analysis. However, intensity images alone are often insufficient for detecting variations in the dielectric constant of a sample, and extraction of material properties without additional phase information requires extensive prior knowledge of the sample. Digital holography provides a means for intensity-only detectors to reconstruct both amplitude and phase images.

Validity of mental and physical stress models.

Different stress models are employed to enhance our understanding of the underlying mechanisms and explore potential interventions. However, the utility of these models remains a critical concern, as their validities may be limited by the complexity of stress processes. Literature review revealed that both mental and physical stress models possess reasonable construct and criterion validities, respectively reflected in psychometrically assessed stress ratings and in activation of the sympathoadrenal system and the hypothalamic-pituitary-adrenal axis.

A double-blind placebo-controlled pilot study of immunoglobulin for small fiber neuropathy associated with TS-HDS and FGFR-3 autoantibodies.

Introduction/aims: Small fiber neuropathies (SFN) have been associated with two autoantibodies, trisulfated heparin disaccharide (TS-HDS) and fibroblast growth factor receptor 3 (FGFR-3), and intravenous immune globulin (IVIG) has been suggested as a potential therapy. The study objective is to determine the efficacy of IVIG on nerve density, pain and neurologic examinations in patients with SFN associated with TS-HDS and FGFR-3 autoantibodies.

Methods: This was a double-blind placebo-controlled pilot study.

Barriers and facilitators to the future uptake of regular COVID-19 booster vaccinations among young adults in the UK.

The evidence of waning immunity offered by COVID-19 vaccines suggests that widespread and regular uptake of routine COVID-19 booster vaccines will be needed. In order to understand the hesitancy toward COVID-19 boosters, we examined the barriers and facilitators to receiving regular COVID-19 boosters in a sample of young adults in the UK. A cross-sectional survey was completed by 423 participants (M = 22.

Slow waves on long helices.

Slowing light in a non-dispersive and controllable fashion opens the door to many new phenomena in photonics. As such, many schemes have been put forward to decrease the velocity of light, most of which are limited in bandwidth or incur high losses. In this paper we show that a long metallic helix supports a low-loss, broadband slow wave with a mode index that can be controlled via geometrical design.

All-optical switching of an epsilon-near-zero plasmon resonance in indium tin oxide.

Nonlinear optical devices and their implementation into modern nanophotonic architectures are constrained by their usually moderate nonlinear response. Recently, epsilon-near-zero (ENZ) materials have been found to have a strong optical nonlinearity, which can be enhanced through the use of cavities or nano-structuring. Here, we study the pump dependent properties of the plasmon resonance in the ENZ region in a thin layer of indium tin oxide (ITO).

High efficiency photomodulators for millimeter wave and THz radiation.

Photomodulators for mm-wave and THz radiation are an essential component for many imaging and signal processing applications. While a myriad of schemes have been devised to enhance photomodulation by enhancing the light-matter interaction, there has been less focus on the photoconductive materials themselves, which are often the limiting factor. Here, we present an approach to increase the photomodulation efficiency of silicon by orders of magnitude, using post treatment of off-the-shelf silicon wafers.

Origins of All-Optical Generation of Plasmons in Graphene.

Graphene, despite its centrosymmetric structure, is predicted to have a substantial second order nonlinearity, arising from non-local effects. However, there is disagreement between several published theories and experimental data. Here we derive an expression for the second order conductivity of graphene in the non-local regime using perturbation theory, concentrating on the difference frequency mixing process, and compare our results with those already published.

The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies.

For many of the envisioned optoelectronic applications of graphene, it is crucial to understand the subpicosecond carrier dynamics immediately following photoexcitation and the effect of photoexcitation on the electrical conductivity-the photoconductivity. Whereas these topics have been studied using various ultrafast experiments and theoretical approaches, controversial and incomplete explanations concerning the sign of the photoconductivity, the occurrence and significance of the creation of additional electron-hole pairs, and, in particular, how the relevant processes depend on Fermi energy have been put forward. We present a unified and intuitive physical picture of the ultrafast carrier dynamics and the photoconductivity, combining optical pump-terahertz probe measurements on a gate-tunable graphene device, with numerical calculations using the Boltzmann equation.

Subwavelength hyperspectral THz studies of articular cartilage.

Terahertz-spectroscopy probes dynamics and spectral response of collective vibrational modes in condensed phase, which can yield insight into composition and topology. However, due to the long wavelengths employed (λ = 300 μm at 1THz), diffraction limited imaging is typically restricted to spatial resolutions around a millimeter. Here, we demonstrate a new form of subwavelength hyperspectral, polarization-resolved THz imaging which employs an optical pattern projected onto a 6 μm-thin silicon wafer to achieve near-field modulation of a co-incident THz pulse.

Reversal of orbital angular momentum arising from an extreme Doppler shift.

The linear Doppler shift is familiar as the rise and fall in pitch of a siren as it passes by. Less well known is the rotational Doppler shift, proportional to the rotation rate between source and receiver, multiplied by the angular momentum carried by the beam. In extreme cases the Doppler shift can be larger than the rest-frame frequency and for a red shift, the observed frequency then becomes "negative.

Enhancing the magneto-optical Kerr effect through the use of a plasmonic antenna.

We employ an extended finite-element model as a design tool capable of incorporating the interaction between plasmonic antennas and magneto-optical effects, specifically the magneto-optical Kerr effect (MOKE). We first test our model in the absence of an antenna and show that for a semi-infinite thin-film, good agreement is obtained between our finite-element model and analytical calculations. The addition of a plasmonic antenna is shown to yield a wavelength dependent enhancement of the MOKE.

A platform for time-resolved scanning Kerr microscopy in the near-field.

Time-resolved scanning Kerr microscopy (TRSKM) is a powerful technique for the investigation of picosecond magnetization dynamics at sub-micron length scales by means of the magneto-optical Kerr effect (MOKE). The spatial resolution of conventional (focused) Kerr microscopy using a microscope objective lens is determined by the optical diffraction limit so that the nanoscale character of the magnetization dynamics is lost. Here we present a platform to overcome this limitation by means of a near-field TRSKM that incorporates an atomic force microscope (AFM) with optical access to a metallic AFM probe with a nanoscale aperture at its tip.

Expression of masculine identity in individuals with a traumatic brain injury.

Primary Objective: This research seeks to examine and describe how four males with a traumatic brain injury (TBI) use language to negotiate their masculine identities.

Research Design: Qualitative research methods were employed with a 'case study' design that allows for a detailed description of the cases, and the interactions examined.

Methods And Procedures: The tools of inquiry applied included a topic analysis, as well as linguistic analysis methods that incorporated the theory of Systemic Functional Linguistics.

Intensity dependences of the nonlinear optical excitation of plasmons in graphene.

Recently, we demonstrated an all-optical coupling scheme for plasmons, which takes advantage of the intrinsic nonlinear optical response of graphene. Frequency mixing using free-space, visible light pulses generates surface plasmons in a planar graphene sample, where the phase matching condition can define both the wavevector and energy of surface waves and intraband transitions. Here, we also show that the plasmon generation process is strongly intensity-dependent, with resonance features washed out for absorbed pulse fluences greater than 0.

Subwavelength Terahertz Imaging of Graphene Photoconductivity.

Using a spatially structured, optical pump pulse with a terahertz (THz) probe pulse, we are able to determine spatial variations of the ultrafast THz photoconductivity with subwavelength resolution (75 μm ≈ λ/5 at 0.8 THz) in a planar graphene sample. We compare our results to Raman spectroscopy and correlate the existence of the spatial inhomogeneities between the two measurements.

On the origin of pure optical rotation in twisted-cross metamaterials.

We present an experimental and computational study of the response of twisted-cross metamaterials that provide near dispersionless optical rotation across a broad band of frequencies from 19 GHz to 37 GHz. We compare two distinct geometries: firstly, a bilayer structure comprised of arrays of metallic crosses where the crosses in the second layer are twisted about the layer normal; and secondly where the second layer is replaced by the complementary to the original, i.e.

Noninvasive, near-field terahertz imaging of hidden objects using a single-pixel detector.

Terahertz (THz) imaging can see through otherwise opaque materials. However, because of the long wavelengths of THz radiation (λ = 400 μm at 0.75 THz), far-field THz imaging techniques suffer from low resolution compared to visible wavelengths.

ns or fs pulsed laser ablation of a bulk InSb target in liquids for nanoparticles synthesis.

Laser ablation of bulk target materials in liquids has been established as an alternative method for the synthesis of nanoparticles colloidal solutions mainly due to the fact that the synthesized nanoparticles have bare, ligand-free surfaces since no chemical precursors are used for their synthesis. InSb is a narrow band gap semiconductor which has the highest carrier mobility of any known semiconductor and nanoparticles of this material are useful in optoelectronic device fabrication. In this paper a bulk InSb target was ablated in deionized (DI) water or ethanol using a nanosecond (20 ns) or a femtosecond (90 fs) pulsed laser source, for nanoparticles synthesis.

Ultrafast optical modification of exchange interactions in iron oxides.

Ultrafast non-thermal manipulation of magnetization by light relies on either indirect coupling of the electric field component of the light with spins via spin-orbit interaction or direct coupling between the magnetic field component and spins. Here we propose a scenario for coupling between the electric field of light and spins via optical modification of the exchange interaction, one of the strongest quantum effects with strength of 10(3) Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be called inverse magneto-refraction, is allowed in a material of any symmetry.