E. Hendry

Universiteit Twente, Enschede, Overijssel, Netherlands

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Publications (73)294.49 Total impact

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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.
  • 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.
    Applied Physics B 07/2015; 120(1). DOI:10.1007/s00340-015-6096-y · 1.86 Impact Factor
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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 %.
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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.
    Physical Review B 11/2014; 90(18). DOI:10.1103/PhysRevB.90.184405 · 3.74 Impact Factor
  • Physical Review B 10/2014; 90(13). DOI:10.1103/PhysRevB.90.139903 · 3.74 Impact Factor
  • 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.
    Physical Review B 08/2014; 90(8). DOI:10.1103/PhysRevB.90.081401 · 3.74 Impact Factor
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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.
    Physical Review B 02/2014; 89(12). DOI:10.1103/PhysRevB.89.125426 · 3.74 Impact Factor
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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.
    The Journal of Physical Chemistry C 01/2014; 118(2):1191-1197. DOI:10.1021/jp406897y · 4.77 Impact Factor
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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.
    Applied Physics Letters 10/2013; 103(15). DOI:10.1063/1.4823552 · 3.30 Impact Factor
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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.
    The Journal of the Acoustical Society of America 09/2013; 134(3):1754-9. DOI:10.1121/1.4817898 · 1.50 Impact Factor
  • 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.
    Physical Review B 07/2013; 88(4). DOI:10.1103/PhysRevB.88.041407 · 3.74 Impact Factor
  • 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.
    Physical review. B, Condensed matter 02/2013; 87(8). DOI:10.1103/PhysRevB.87.085405 · 3.66 Impact Factor
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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.
    Physical review. B, Condensed matter 06/2012; 85(21):214305-. DOI:10.1103/PhysRevB.85.214305 · 3.66 Impact Factor
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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.
    Nano Letters 05/2012; 12(7):3640-4. DOI:10.1021/nl3012787 · 13.59 Impact Factor
  • E. K. Stone · E. Hendry
    Physical review. B, Condensed matter 03/2012; 85(12). DOI:10.1103/PhysRevB.85.129901 · 3.66 Impact Factor
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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.
    Physical review. B, Condensed matter 02/2012; 85(16). DOI:10.1103/PhysRevB.85.161411 · 3.66 Impact Factor
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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.
    Nano Letters 02/2012; 12(2):977-83. DOI:10.1021/nl204055r · 13.59 Impact Factor
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    ABSTRACT: The acoustic transmittance of two closely spaced rigid plates perforated with a square array of circular holes is studied both experimentally and numerically. The system exhibits a band of acoustic attenuation originating from hybridization between a two-dimensional resonance in the gap between the plates, and pipe modes in the holes. Misalignment of the holes in either one or both lateral dimensions shifts the centre frequency of the stop band to maintain the conditions required for zero transmission.
    Meta '12, Paris; 01/2012
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    ABSTRACT: Graphene shows great potential for future electronic devices due to its high carrier mobility and thermal conductivity [1, 2]. An important consideration for such devices is thermal cooling of charge carriers. The use of large current densities results in over heating of charge carriers, and this power must be dissipated to avoid thermal breakdown of the graphene sheet [3]. The main cooling mechanisms are (1) direct transfer of heat to the metallic contacts forming the source and drain of the device via diffusion of electrons [4], (2) transfer of heat to the graphene lattice via scattering of electrons by acoustic phonons of the graphene sheet [5], and (3) transfer of heat directly to the underlying substrate via scattering of electrons by surface mode phonons of the substrate [6].
    Nanotechnology (IEEE-NANO), 2012 12th IEEE Conference on; 01/2012
  • D K Polyushkin · E Hendry · E K Stone · W L Barnes
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    ABSTRACT: We investigate the generation of THz pulses when arrays of silver nanoparticles are irradiated by femtosecond laser pulses, providing the first reproducible experimental evidence in support of recent theoretical predictions of such an effect. We assess our results in the context of a model where photoelectrons are produced by plasmon-mediated multiphoton excitation, and THz radiation is generated via the acceleration of the ejected electrons by ponderomotive forces arising from the inhomogeneous plasmon field. By exploring the dependence of the THz emission on the femtosecond pulse intensity and as a function of metal nanoparticle morphology, and by comparing measurements to numerical modeling, we are able to verify the role of the particle plasmon mode in this process.
    Nano Letters 11/2011; 11(11):4718-24. DOI:10.1021/nl202428g · 13.59 Impact Factor

Publication Stats

2k Citations
294.49 Total Impact Points


  • 2014
    • Universiteit Twente
      • Department of Complex Photonic Systems (COPS)
      Enschede, Overijssel, Netherlands
  • 2007–2014
    • University of Exeter
      • Department of Physics and Astronomy
      Exeter, England, United Kingdom
  • 2008
    • FOM Institute AMOLF
      Amsterdamo, North Holland, Netherlands
  • 2004–2005
    • Leiden University
      Leyden, South Holland, Netherlands