9,096 research outputs found
1.57 Îźm InGaAsP/InP surface emitting lasers by angled focus ion beam etching
The characteristics of 1.57 Οm InGaAsP/InP surface emitting lasers based on an in-plan ridged structure and 45° beam deflectors defined by angled focused ion beam (FIB) etching are reported. With an externally integrated beam deflector, threshold currents and emission spectra identical to conventional edge emitting lasers are achieved. These results show that FIB etching is a very promising technique for the definition of high quality mirrors and beam deflectors on semiconductor heterostructures for a variety of integrated optoelectronic devices
Tests of Lorentz and CPT symmetry with hadrons and nuclei
We apply chiral-perturbation-theory techniques to the QCD sector of the Lorentz and CPT violating standard-model extension. We derive the effective Lagrangian in terms of pions and nucleons for a selected set of dimension-five operators involving quarks and gluons. This derivation is based on chiral-symmetry properties of the operators, as well as on their behaviour under C,P, and T transformations. We consider the power counting rules and apply the heavy-baryon approach to account for the large nucleon mass. Having obtained the relevant Lorentz-violating contributions to the pion-nucleon Lagrangian, we proceed to derive the particle and anti-particle Hamiltonian, from which we obtain the Lorentz-violating contribution to comagnetometer experiments. This allows us to place stringent limits on some of the parameters. For some other parameters we find that the best bounds will come from nucleon nucleon interactions, and we derive the relevant nucleon-nucleon potential. These considerations imply possible new opportunities for spin-precession experiments involving for example the deuteron.Portuguese Foundation for Science and Technology (FCT) [SFRH/BPD/101403/2014]; program POPH/FS
Formation of Low Threshold Voltage Microlasers
Vertical cavity surface emitting lasers (VCSELs) with threshold voltages of 1.7V have been fabricated. The resistance-area product in these new vertical cavity lasers is comparable to that of edge-emitting lasers, and threshold currents as low as 3 mA have been measured. Molecular beam epitaxy was used to grow n-type mirrors, a quantum well active region, and a heavily Be-doped p-contact. After contact definition and alloying, passive high-reflectivity mirrors were deposited by reactive sputter deposition of SiO2/Si3N4 to complete the laser cavity
Quantitative effects of abrupt deceleration on pulmonary diffusion in man Technical report,
Quantitative effects of abrupt deceleration on pulmonary diffusion in ma
Monolithic InP-Based Grating Spectrometer for Wavelength-Division Multiplexed Systems at 1.5 Îźm
A monolithic InP-based grating spectrometer for use in wavelength-division multiplexed systems at 1.5 Îźm is reported.
The spectrometer uses a single etched reflective focusing diffraction grating and resolves >50 channels at 1 nm spacing with a ~0.3nm channel width and at least 19dB channel isolation. Operation is essentially of the state of the input polarisation
Room temperature photonic crystal defect lasers at near-infrared wavelengths in InGaAsP
Room temperature lasing from optically pumped single defects in a two-dimensional (2-D) photonic bandgap (PBG) crystal is demonstrated. The high-Q optical microcavities are formed by etching a triangular array of air holes into a half-wavelength thick multiquantum-well waveguide. Defects in the 2-D photonic crystal are used to support highly localized optical modes with volumes ranging from 2 to 3 (lambda/2n)(3). Lithographic tuning of the air hole radius and the lattice spacing are used to match the cavity wavelength to the quantum-well gain peak, as well as to increase the cavity Q. The defect lasers were pumped with 10-30 ns pulses of 0.4-1% duty cycle. The threshold pump power was 1.5 mW (approximate to 500 ÎźW absorbed)
Planar photonic crystal
We present results of guiding light in a single-line-defect planar photonic crystal (PPC) waveguide with 90° and 60° bends. The wave guiding is obtained by total internal reflection perpendicular to the plane of propagation and by the photonic band gap for the 2D photonic crystal in the plane. The results for photonic waveguiding are shown and demonstrated at 1.5 ¾m wavelength
Optimized time-dependent perturbation theory for pulse-driven quantum dynamics in atomic or molecular systems
We present a time-dependent perturbative approach adapted to the treatment of
intense pulsed interactions. We show there is a freedom in choosing secular
terms and use it to optimize the accuracy of the approximation. We apply this
formulation to a unitary superconvergent technique and improve the accuracy by
several orders of magnitude with respect to the Magnus expansion.Comment: 4 pages, 2 figure
Knight Shift and Leading Superconducting Instability From Spin Fluctuations in Sr2RuO4
Recent nuclear magnetic resonance studies [A. Pustogow {\it et al.},
arXiv:1904.00047] have challenged the prevalent chiral triplet pairing scenario
proposed for SrRuO. To provide guidance from microscopic theory as to
which other pair states might be compatible with the new data, we perform a
detailed theoretical study of spin-fluctuation mediated pairing for this
compound. We map out the phase diagram as a function of spin-orbit coupling,
interaction parameters, and band-structure properties over physically
reasonable ranges, comparing when possible with photoemission and inelastic
neutron scattering data information. We find that even-parity pseudospin
singlet solutions dominate large regions of the phase diagram, but in certain
regimes spin-orbit coupling favors a near-nodal odd-parity triplet
superconducting state, which is either helical or chiral depending on the
proximity of the band to the van Hove points. A surprising
near-degeneracy of the nodal - and -wave solutions leads
to the possibility of a near-nodal time-reversal symmetry broken
pair state. Predictions for the temperature dependence
of the Knight shift for fields in and out of plane are presented for all
states.Comment: 5 pages (3 figures) + supplementary informatio
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