Regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) when 11 subjects made plausibility judgments about written sentences that varied in their syntactic complexity. While making their judgments, subjects uttered the word "double" aloud at a rate of one utterance per second to inhibit their ability to rehearse the sentences. Blood flow increased in Broca's area when subjects made judgments about the more complex sentences. This result replicates and extends previous findings that blood flow increases in this region when subjects process complex syntax under no interference conditions. The results of this experiment provide strong evidence that the increase in blood flow seen in Broca's area in association with processing syntactically complex structures is not due to subvocal rehearsal of those structures, but rather results from processing syntactic forms themselves.

Plasmonic antennas can enhance the intensity of a nanojoule laser pulse by localizing the electric field in their proximity 1 . It has been proposed that the field can become strong enough to convert the fundamental laser frequency into high-order harmonics through an extremely nonlinear interaction with gas atoms that occupy the nanoscopic volume surrounding the antennas [2][3][4] . However, the small number of gas atoms that can occupy this volume limits the generation of high harmonics [5][6][7] . Here we use an array of monopole nano-antennas to demonstrate plasmon-assisted high-harmonic generation directly from the supporting crystalline silicon substrate. The high density of the substrate compared with a gas allows macroscopic buildup of harmonic emission. Despite the sparse coverage of antennas on the surface, harmonic emission is ten times brighter than without antennas. Imaging the high-harmonic radiation will allow nanometre and attosecond measurement of the plasmonic field 8 thereby enabling more sensitive plasmon sensors 9 while opening a new path to extreme-ultraviolet-frequency combs 10

Surface plasmon sub-bandgap Schottky detectors based on an asymmetric Au stripe waveguide on p-Si are investigated theoretically and experimentally at free-space wavelengths of λ(0) = 1310 and 1550 nm. Au on p-Si produces a low Schottky barrier (0.33 eV), which improves the internal quantum efficiency. Thick and thin Au stripes are compared, with the latter increasing the hot hole emission probability relative to the former, and thus also improving the internal quantum efficiency. Two excitation schemes are considered: end facet illumination which launches surface plasmons on the detector, and top illumination which does not. Both schemes are implemented using a piezoelectric positioner that is programmed to scan the detection area in steps of 100-200 nm, thus enabling the acquisition of high-resolution photocurrent maps. The surface plasmon detectors yield a responsivity of ~1 mA W(-1), ~2× larger than the same detectors under top illumination, due to the absorption of surface plasmons. We compare the measurements with theoretical results for both excitation schemes and estimate the hot hole attenuation length in our Au stripes to be ~23 nm.

We propose a plasmonic surface that produces an electrically controlled reflectance as a high-speed intensity modulator. The device is conceived as a metal-oxide-semiconductor capacitor on silicon with its metal structured as a thin patch bearing a contiguous nanoscale grating. The metal structure serves multiple functions as a driving electrode and as a grating coupler for perpendicularly incident p-polarized light to surface plasmons supported by the patch. Modulation is produced by charging and discharging the capacitor and exploiting the carrier refraction effect in silicon along with the high sensitivity of strongly confined surface plasmons to index perturbations. The area of the modulator is set by the area of the incident beam, leading to a very compact device for a strongly focused beam (∼2.5 μm in diameter). Theoretically, the modulator can operate over a broad electrical bandwidth (tens of gigahertz) with a modulation depth of 3 to 6%, a loss of 3 to 4 dB, and an optical bandwidth of about 50 nm. About 1000 modulators can be integrated over a 50 mm(2) area producing an aggregate electro-optic modulation rate in excess of 1 Tb/s. We demonstrate experimentally modulators operating at telecommunications wavelengths, fabricated as nanostructured Au/HfO2/p-Si capacitors. The modulators break conceptually from waveguide-based devices and belong to the same class of devices as surface photodetectors and vertical cavity surface-emitting lasers.

Background: The administration of antiplatelet drugs before coronary artery bypass graft surgery (CABG) is associated with an increased risk of major hemorrhage and related surgical reexploration. Little is known about the relative effect of combined clopidogrel and aspirin on blood product use around the time of CABG. We evaluated the associated risk between the combined use of aspirin and clopidogrel and the transfusion of blood products perioperatively.

In this paper we present a sub-bandgap photodetector consisting of a metal grating on a thin metal patch on silicon, which makes use of the enhancement produced by the excitation of surface plasmon polaritons at the metal-silicon interface. The grating is defined via e-beam lithography and Au lift-off on a Au patch defined beforehand by optical lithography on doped p-type silicon. The surface plasmon polaritons are absorbed by the metal, leading to the creation of hot holes that can cross into the silicon where they are collected as the photocurrent. Physical characterization of intermediate structure is provided along with responsivity measurements at telecom wavelengths. Results are promising in terms of responsivity, with a value of 13 mA/W measured at 1550 nm - this is among the highest values reported to date for sub-bandgap detectors based on internal photoemission. The Schottky photodetector can be used in, e.g., non-contact wafer probing or in short-reach optical communications applications.

We propose and demonstrate a thin Au stripe on a truncated 1D dielectric photonic crystal covered with Cytop as a waveguide for Bloch long-range surface plasmon polaritons. High-quality mode outputs were observed and a mode power attenuation of 12–17 dB/mm measured at λ0 = 1310 nm for propagation in the plane of the truncated photonic crystal and within its stopband. The truncated 1D photonic crystal advantageously enables the use of a large range of materials for the substrate, breaking free from the constraint of material symmetry to support long-range plasmons. An input grating coupler implemented as a periodic array of nanoscale Au ridges on a Au stripe was used to excite the mode via perpendicularly incident p-polarized light. The output was provided by adding a second grating coupler near the end of a waveguide to diffract light upward or by polishing the output facet and allowing the mode to radiate into a free-space beam. Advantageously, grating coupling eliminates the need for high-quality end facets, and optical alignment is simplified. Given its practicality, the structure proposed is of strong interest for biosensing.

Exploiting surface plasmon polaritons to enhance interactions between graphene and light has recently attracted much interest. In particular, nonlinear optical processes in graphene can be dramatically enhanced and controlled by plasmonic nanostructures. This work demonstrates Raman scattering enhancement in graphene based on plasmonic resonant enhancement of the Stokes emission, and compares this mechanism with the conventional Raman enhancement by resonant pump absorption. Arrays of optical nanoantennas with different resonant frequency are utilized to independently identify the effects of each mechanism on Raman scattering in graphene via the measured enhancement factor and its spectral linewidth. We demonstrate that, while both mechanisms offer large enhancement factors (scattering cross-section gains of 160 and 20 for individual nanoantennas, respectively), they affect the graphene Raman spectrum quite differently. Our results provide a benchmark to assess and quantify the role and merit of each mechanism in surface-plasmon-mediated Raman scattering in graphene, and may be employed for design and realization of a variety of graphene optoelectronic devices involving nonlinear optical processes.