1,365 research outputs found
An all-fibre PM MOPA pumped high-power OPO at 3.82 microns based on large aperture PPMgLN
We report a large aperture PPMgLN based OPO generating 21W of average output power at a slope efficiency of 45%, pumped by the output from a polarization maintaining Ytterbium doped fiber MOPA operating at 1060nm producing 58W of average output power and 20ns pulses at a repetition rate of 100kHz. A maximum of 5.5W of optical power was recorded at the idler wavelength of 3.82µm without thermal roll-off. We have experimentally verified that the pulse rise/fall time plays a significant role in the OPO conversion efficiency and that further enhancement in the OPO conversion efficiency will be possible using sub-nanosecond rise and fall times
Optical detection and modulation at 2µm-2.5µm in silicon
Recently the 2µm wavelength region has emerged as an exciting prospect for the next generation of telecommunications. In this paper we experimentally characterise silicon based plasma dispersion effect optical modulation and defect based photodetection in the 2-2.5µm wavelength range. It is shown that the effectiveness of the plasma dispersion effect is dramatically increased in this wavelength window as compared to the traditional telecommunications wavelengths of 1.3µm and 1.55µm. Experimental results from the defect based photodetectors show that detection is achieved in the 2-2.5µm wavelength range, however the responsivity is reduced as the wavelength is increased away from 1.55µm
Hilbert forms for a Finsler metrizable projective class of sprays
The projective Finsler metrizability problem deals with the question whether
a projective-equivalence class of sprays is the geodesic class of a (locally or
globally defined) Finsler function. In this paper we use Hilbert-type forms to
state a number of different ways of specifying necessary and sufficient
conditions for this to be the case, and we show that they are equivalent. We
also address several related issues of interest including path spaces, Jacobi
fields, totally-geodesic submanifolds of a spray space, and the equivalence of
path geometries and projective-equivalence classes of sprays.Comment: 23 page
The multiplier approach to the projective Finsler metrizability problem
This paper is concerned with the problem of determining whether a
projective-equivalence class of sprays is the geodesic class of a Finsler
function. We address both the local and the global aspects of this problem. We
present our results entirely in terms of a multiplier, that is, a type (0,2)
tensor field along the tangent bundle projection. In the course of the analysis
we consider several related issues of interest including the positivity and
strong convexity of positively-homogeneous functions, the relation to the
so-called Rapcs\'ak conditions, some peculiarities of the two-dimensional case,
and geodesic convexity for sprays.Comment: 25 page
The High Redshift Integrated Sachs-Wolfe Effect
In this paper we rely on the quasar (QSO) catalog of the Sloan Digital Sky
Survey Data Release Six (SDSS DR6) of about one million photometrically
selected QSOs to compute the Integrated Sachs-Wolfe (ISW) effect at high
redshift, aiming at constraining the behavior of the expansion rate and thus
the behaviour of dark energy at those epochs. This unique sample significantly
extends previous catalogs to higher redshifts while retaining high efficiency
in the selection algorithm. We compute the auto-correlation function (ACF) of
QSO number density from which we extract the bias and the stellar
contamination. We then calculate the cross-correlation function (CCF) between
QSO number density and Cosmic Microwave Background (CMB) temperature
fluctuations in different subsamples: at high z>1.5 and low z<1.5 redshifts and
for two different choices of QSO in a conservative and in a more speculative
analysis. We find an overall evidence for a cross-correlation different from
zero at the 2.7\sigma level, while this evidence drops to 1.5\sigma at z>1.5.
We focus on the capabilities of the ISW to constrain the behaviour of the dark
energy component at high redshift both in the \LambdaCDM and Early Dark Energy
cosmologies, when the dark energy is substantially unconstrained by
observations. At present, the inclusion of the ISW data results in a poor
improvement compared to the obtained constraints from other cosmological
datasets. We study the capabilities of future high-redshift QSO survey and find
that the ISW signal can improve the constraints on the most important
cosmological parameters derived from Planck CMB data, including the high
redshift dark energy abundance, by a factor \sim 1.5.Comment: 20 pages, 18 figures, and 7 table
On the temperature dependence of the symmetry energy
We perform large-scale shell model Monte Carlo (SMMC) calculations for many
nuclei in the mass range A=56-65 in the complete pfg_{9/2}d_{5/2} model space
using an effective quadrupole-quadrupole+pairing residual interaction. Our
calculations are performed at finite temperatures between T=0.33-2 MeV. Our
main focus is the temperature dependence of the symmetry energy which we
determine from the energy differences between various isobaric pairs with the
same pairing structure and at different temperatures. Our SMMC studies are
consistent with an increase of the symmetry energy with temperature. We also
investigate possible consequences for core-collapse supernovae events
Effect of an Electron-phonon Interaction on the One-electron Spectral Weight of a d-wave Superconductor
We analyze the effects of an electron-phonon interaction on the one-electron
spectral weight A(k,omega) of a d_{x^2-y^2} superconductor. We study the case
of an Einstein phonon mode with various momentum-dependent electron-phonon
couplings and compare the structure produced in A(k,omega) with that obtained
from coupling to the magnetic pi-resonant mode. We find that if the strength of
the interactions are adjusted to give the same renormalization at the nodal
point, the differences in A(k,omega) are generally small but possibly
observable near k=(pi,0).Comment: 10 pages, 14 figures (color versions of Figs. 2,4,10,11,12 available
upon request
Surface electronic structure of Sr2RuO4
We have addressed the possibility of surface ferromagnetism in Sr2RuO4 by
investigating its surface electronic states by angle-resolved photoemission
spectroscopy (ARPES). By cleaving samples under different conditions and using
various photon energies, we have isolated the surface from the bulk states. A
comparison with band structure calculations indicates that the ARPES data are
most readily explained by a nonmagnetic surface reconstruction.Comment: 4 pages, 4 figures, RevTex, submitted to Phys. Rev.
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