E. Hendry

University of Exeter, Exeter, England, United Kingdom

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Publications (77)317.45 Total impact

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    ABSTRACT: We present measurements and analytical modeling which demonstrate enhanced THz transmission through a subwavelength aperture via light-induced diffraction. Our experiment involves photoexciting a conducting pattern onto a silicon interface so as to control and modulate the near-field interference of THz radiation. To illustrate the concept, we photoexcite a simple double-conducting stripe pattern on the incident side of a silicon wafer which has a slit etched into a gold film on the exit side. We show that under certain resonant conditions set by the stripe dimensions, a constructive near-field interference can bring about enhanced transmission through the slit. By raster scanning the excitation pattern under these resonant conditions, one can build an image of subwavelength features such as the slit aperture of our sample.
    No preview · Article · Oct 2015 · Physical Review A
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    ABSTRACT: Terahertz (THz) imaging has the ability to see through otherwise opaque materials. However, due to the long wavelengths of THz radiation ({\lambda}=300{\mu}m at 1THz), far-field THz imaging techniques are heavily outperformed by optical imaging in regards to the obtained resolution. In this work we demonstrate near-field THz imaging with a single-pixel detector. We project a time-varying optical mask onto a silicon wafer which is used to spatially modulate a pulse of THz radiation. The far-field transmission corresponding to each mask is recorded by a single element detector and this data is used to reconstruct the image of an object placed on the far side of the silicon wafer. We demonstrate a proof of principal application where we image a printed circuit board on the underside of a 115{\mu}m thick silicon wafer with ~100{\mu}m ({\lambda}/4) resolution. With subwavelength resolution and the inherent sensitivity to local conductivity provided by the THz probe frequencies, we show that it is possible to detect fissures in the circuitry wiring of a few microns in size. Imaging systems of this type could have other uses where non-invasive measurement or imaging of concealed structures with high resolution is necessary, such as in semiconductor manufacturing or in bio-imaging.
    Full-text · Article · Sep 2015
  • D. K. Polyushkin · E. Hendry · W. L. Barnes
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    ABSTRACT: We report on THz frequency generation via irradiation of microstructured semicontinuous silver films by femtosecond laser pulses. By patterning the film so as to produce an array of microstrips, we show that one can use periodic microstructure to control the way nanostructured metal films produce THz radiation when illuminated by femtosecond infrared laser pulses. A simple analytical model based on the field distribution arising from an array of THz dipole emitters is used to assess the experimental data, allowing us to explain some of the main features of the generated THz radiation patterns, including the strongly resonant features of the emission spectrum.
    No preview · Article · Jul 2015 · Applied Physics B
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    ABSTRACT: Here we present an all-optical plasmon coupling scheme, utilising the intrinsic nonlinear optical response of graphene. We demonstrate coupling of free-space, visible light pulses to the surface plasmons in a planar, un-patterned graphene sheet by using nonlinear wave mixing to match both the wavevector and energy of the surface wave. By carefully controlling the phase-matching conditions, we show that one can excite surface plasmons with a defined wavevector and direction across a large frequency range, with an estimated photon efficiency in our experiments approaching $10^{-5}$.
    Preview · Article · May 2015 · Nature Physics
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    ABSTRACT: Here we report experiments performed on orthoferrites by means of THz time-domain emission spectroscopy. We show that the femtosecond laser pulses excite both iron and rare-earth sub-systems on sub-picosecond timescale. In particular, the novel route to the optical control of the exchange interaction has been discovered.
    No preview · Article · Jan 2015
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    ABSTRACT: 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 novel scenario for coupling between the electric field of light and spins via optical modification of the exchange interaction, one of the strongest quantum effects, the strength of which can reach 1000 Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be called the inverse magneto-refraction, is allowed in a material of any symmetry. Its existence is corroborated by the experimental observation of THz emission by magnetic-dipole active spin resonances optically excited in a broad class of iron oxides with a canted spin configuration. From its strength we estimate that a sub-picosecond laser pulse with a moderate fluence of ~ 1 mJ/cm^2 acts as a pulsed effective magnetic field of 0.01 Tesla, arising from the optically perturbed balance between the exchange parameters. Our findings are supported by a low-energy theory for the microscopic magnetic interactions between non-equilibrium electrons subjected to an optical field which suggests a possibility to modify the exchange interactions by light over 1 %.
    Full-text · Article · Dec 2014
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    ABSTRACT: Using the examples of laser-induced spin-reorientation phase transitions in ${\mathrm{TmFeO}}_{3}$ and ${\mathrm{ErFeO}}_{3}$ orthoferrites, we demonstrate that terahertz emission spectroscopy can obtain novel information about ultrafast laser-induced spin dynamics, which is not accessible by more common all-optical methods. The power of the method is evidenced by the fact that, in addition to the expected quasi-ferromagnetic and quasi-antiferromagnetic modes of the iron sublattices, terahertz emission spectroscopy enables detection of a resonance optically excited at an unexpected frequency of $\sim${}0.3\char21{}0.35 THz. By recording how the amplitude and phase of the excited oscillations depend on temperature and applied magnetic field, we show that the unexpected mode has all the features of a spin resonance of the ${\mathrm{Fe}}^{3+}$ ions. We suggest that it can be assigned to transitions between the multiplet sublevels of the ${}^{6}{A}_{1}$ ground state of the ${\mathrm{Fe}}^{+3}$ ions occupying rare-earth positions.
    No preview · Article · Nov 2014 · Physical Review B

  • No preview · Article · Oct 2014 · Physical Review B
  • S. M. Hornett · M. Heath · D. W. Horsell · E. Hendry
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    ABSTRACT: Recently, there has been a great deal of interest in the effect of atmospheric gases on the properties of graphene. We investigate the electrical and optical response of graphene-based field effect transistors that have been exposed to high purity oxygen gas using a combination of ultrafast two-pulse correlation (to give high temporal resolution) and low-frequency transport measurements (to monitor the photoinduced changes in the Fermi level). By measuring the Fermi level shifts, we are only sensitive to the oxygen atoms that interact directly with the surface. We compare our results to predictions of the empirical friction model for molecular desorption. We show the time scale of the relaxation associated with oxygen desorption to be similar to 100 fs, suggesting the desorption proceeds through hot electron generation in the graphene rather than heating of the lattice through hot phonon generation.
    No preview · Article · Aug 2014 · Physical Review B
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    ABSTRACT: 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.
    No preview · Article · Feb 2014 · Physical Review B
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    ABSTRACT: Films of colloidal TiO2 nanoparticles are widely used in photovoltaic and photocatalytic applications, and the nature of electrical conductivity in such materials is therefore of both fundamental and practical interest. The conductive properties of colloid TiO2 films depend strongly on their morphology and deviate greatly from the properties of the bulk material. We report ultrafast photoconductivity studies of films consisting of sintered TiO2 particles of very different sizes performed using time-resolved terahertz spectroscopy. Remarkably, identical photoconductivity spectra are observed for films of particles with diameters of tens and hundreds of nanometers, respectively. The independence of photoconductivity on particle size directly demonstrates that the terahertz photoconductive response of colloidal TiO2 films is not affected by carrier backscattering at particle boundaries as has previously been concluded, but rather by depolarization fields resulting from the spatial inhomogeneities in the dielectric function inherent to these types of films. Modeling of the influence of depolarization fields on the terahertz conductivity allows us to explain the measured data and gain insights into the morphology of the film. Specifically, we show that the observed photoconductivity spectra reflect percolated pathways in the colloidal TiO2 nanoparticles films, through which charge carrier diffusion can occur over macroscopic length scales.
    Full-text · Article · Jan 2014 · The Journal of Physical Chemistry C
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    E. Alexeev · J. Moger · E. Hendry
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    ABSTRACT: The modification of single layer graphene due to intense, picoseconds near-infrared laser pulses is investigated. We monitor the stable changes introduced to graphene upon photoexcitation using Raman spectroscopy. We find that photoexcitation leads to both a local increase in hole doping and a reduction in compressive strain. Possible explanations for these effects, due to photo-induced oxygenation and photo-induced buckling of the graphene, are discussed.
    Full-text · Article · Oct 2013 · Applied Physics Letters
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    ABSTRACT: The acoustic transmittance of two closely spaced solid plates, each perforated with a square array of cylindrical holes, exhibits a band of near-perfect acoustic attenuation originating from hybridization between a resonance in the gap separating the plates and pipe resonances in the holes. Displacement of one plate relative to the other, such that the holes are no longer aligned, or an increase in the plate separation leads to an increased center frequency of the stop band. This ability to easily tune the frequency of the stop band may prove advantageous.
    No preview · Article · Sep 2013 · The Journal of the Acoustical Society of America
  • Nina Meinzer · Euan Hendry · William L. Barnes
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    ABSTRACT: We investigate the chiral properties of near fields around plasmonic nanostructures and their relation to the electromagnetic chirality C. By combining chiral metal nanoparticles with achiral dye molecules and measuring the circular polarization dependence of the enhanced photoluminescence, we find a correlation between the dissymmetry of the luminescence enhancement and the calculated values of C. These effects are strong (∼10−1), despite the weak circular dichroism of the particles (∼10−5). We further show that C represents the chiral selectivity of the near-field coupling between an emitter and a nanoantenna.
    No preview · Article · Jul 2013 · Physical Review B
  • T. J. Davis · E. Hendry
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    ABSTRACT: We show theoretically that localized surface plasmons can generate optical fields with a chirality exceeding that of circularly polarized light by a factor of 50. This superchiral optical field can be formed from linearly polarized light incident on nonchiral metal structures. We identify three mechanisms that lead to large optical chirality involving the coupling between the incident light and the evanescent fields of the surface plasmons. Two of these mechanisms create superchiral regions with nonzero average chirality suitable for the excitation of chiral molecules in solution.
    No preview · Article · Feb 2013 · Physical review. B, Condensed matter
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    ABSTRACT: The “acoustic double fishnet” is a structure with holes running from its front to back faces, yet at a characteristic frequency it transmits very little sound. The transmittance of this structure, which is comprised of a pair of closely spaced, periodically perforated plates, is determined experimentally and analytically. The surprising acoustic properties are due to hybridization between a two-dimensional resonance within the gap between the plates, and pipe modes within the holes. At the center of the stop band the input impedance is imaginary, interpreted as a negative product of effective bulk modulus and density.
    Full-text · Article · Jun 2012 · Physical review. B, Condensed matter
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    ABSTRACT: Using a modal matching theory, we demonstrate the generation of short-range, chiral electromagnetic fields via the excitation of arrays of staggered nanoslits that are chiral in two dimensions. The electromagnetic near fields, which exhibit a chiral density greater than that of circularly polarized light, can enhance the chiroptical interactions in the vicinity of the nanoslits. We discuss the features of nanostructure symmetry required to obtain the chiral fields and explicitly show how these structures can give rise to detection and characterization of materials with chiral symmetry.
    Full-text · Article · May 2012 · Nano Letters
  • E. K. Stone · E. Hendry

    No preview · Article · Mar 2012 · Physical review. B, Condensed matter
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    ABSTRACT: We have experimentally studied the nonlinear nature of electrical conduction in monolayer graphene devices on silica substrates. This nonlinearity manifests itself as a nonmonotonic dependence of the differential resistance on applied DC voltage bias across the sample. At temperatures below ~70K, the differential resistance exhibits a peak near zero bias that can be attributed to self-heating of the charge carriers. We show that the shape of this peak arises from a combination of different energy dissipation mechanisms of the carriers. The energy dissipation at higher carrier temperatures depends critically on the length of the sample. For samples longer than 10um the heat loss is shown to be determined by optical phonons at the silica-graphene interface.
    Full-text · Article · Feb 2012 · Physical review. B, Condensed matter
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    ABSTRACT: We report a new approach for creating chiral plasmonic nanomaterials. A previously unconsidered, far-field mechanism is utilized which enables chirality to be conveyed from a surrounding chiral molecular material to a plasmonic resonance of an achiral metallic nanostructure. Our observations break a currently held preconception that optical properties of plasmonic particles can most effectively be manipulated by molecular materials through near-field effects. We show that far-field electromagnetic coupling between a localized plasmon of a nonchiral nanostructure and a surrounding chiral molecular layer can induce plasmonic chirality much more effectively (by a factor of 10(3)) than previously reported near-field phenomena. We gain insight into the mechanism by comparing our experimental results to a simple electromagnetic model which incorporates a plasmonic object coupled with a chiral molecular medium. Our work offers a new direction for the creation of hybrid molecular plasmonic nanomaterials that display significant chiroptical properties in the visible spectral region.
    Full-text · Article · Feb 2012 · Nano Letters

Publication Stats

2k Citations
317.45 Total Impact Points


  • 2006-2015
    • University of Exeter
      • • College of Engineering, Mathematics and Physical Sciences
      • • Department of Physics and Astronomy
      Exeter, England, United Kingdom
  • 2014
    • Universiteit Twente
      • Department of Complex Photonic Systems (COPS)
      Enschede, Overijssel, Netherlands
  • 2008
    • FOM Institute AMOLF
      Amsterdamo, North Holland, Netherlands
  • 2004-2005
    • Leiden University
      Leyden, South Holland, Netherlands