894 research outputs found
Fabrication and measurement of a photonic crystal waveguide integrated with a semiconductor optical amplifier
A III-V semiconductor photonic crystal (PhC) waveguide is integrated into a semiconductor optical amplifier (SOA); this has the potential to reshape pulses that are distorted and chirped on propagation through the SOA. The PhC waveguide is modeled using the three-dimensional (3D) finite difference time domain (FDTD) method initially for the ideal case of infinite depth holes, and this shows a ministop band close to 1600 nm. The PhC waveguide is then fabricated into a commercial SOA using focused ion beam etching. The optical power measured at the output of the PhC-SOA waveguide shows evidence of a ministop band but with a small stopband depth. More realistic 3D FDTD modeling including effects of finite hole depth and vertical layer structure is then shown to give much better agreement with measured results. Finally predictions are made for the performance of a membrane structure
Single Lateral Mode Mid-Infrared Laser Diode using Sub-Wavelength Modulation of the Facet Reflectivity
The characteristics of mid-infrared laser diodes have been investigated
before and after the patterning of sub-wavelength metallic apertures on the
emitting facet. Before modification of the facet the emitted spectrum consisted
of a large number of peaks associated with different spatial modes, whereas
afterwards the spectrum was dominated by a single peak. Simulations showed that
the patterning of the facet caused the effective reflectivity to be different
for each lateral mode, suggesting that the peak in the measured spectra is
associated with the single lateral mode which is most strongly reflected from
the modified facet.Comment: 12 pages, 3 figure
Streaking single-electron ionization in open-shell molecules driven by X-ray pulses
We obtain continuum molecular wavefunctions for open-shell molecules in the
Hartree-Fock framework. We do so while accounting for the singlet or triplet
total spin symmetry of the molecular ion, that is, of the open-shell orbital
and the initial orbital where the electron ionizes from. Using these continuum
wavefunctions, we obtain the dipole matrix elements for a core electron that
ionizes due to single-photon absorption by a linearly polarized X-ray pulse.
After ionization from the X-ray pulse, we control or streak the electron
dynamics using a circularly polarized infrared (IR) pulse. For a high intensity
IR pulse and photon energies of the X-ray pulse close to the ionization
threshold of the or orbitals, we achieve control of the
angle of escape of the ionizing electron by varying the phase delay between the
X-ray and IR pulses. For a low intensity IR pulse, we obtain final electron
momenta distributions on the plane of the IR pulse and we find that many
features of these distributions correspond to the angular patterns of electron
escape solely due to the X-ray pulse.Comment: 13 pages, 7 figure
Integronlike Structures in Campylobacter spp. of Human and Animal Origin
Resistance to antimicrobial agents used to treat severe Campylobacter spp. gastroenteritis is increasing worldwide. We assessed the antimicrobial resistance patterns of Campylobacter spp. isolates of human and animal origin. More than half (n = 32) were resistant to sulphonamide, a feature known to be associated with the presence of integrons. Analysis of these integrons will further our understanding of Campylobacter spp. epidemiology
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