12,149 research outputs found
Cascaded Nondegenerate Four-Wave Mixing Technique for High-Power Single-Cycle Pulse Synthesis in the Visible and Ultraviolet Ranges
We present a new technique to synthesize high-power single-cycle pulses in
the visible and ultraviolet ranges by coherent superposition of a multiband
octave-spanning spectrum obtained by highly-nondegenerate cascaded four-wave
mixing of femtosecond pulses in bulk isotropic nonresonant media. The
generation of coherent spectra spanning over two octaves in bandwidth is
experimentally demonstrated using a thin fused silica slide. Full
characterization of the intervening multicolored fields using
frequency-resolved optical gating, where multiple cascaded orders have been
measured simultaneously for the first time, supports the possibility of direct
synthesis of near-single-cycle 2.2 fs visible-UV pulses without recurring to
complex amplitude or phase control, which should enable many applications in
science and technology.Comment: 13 pages, 4 figures. Submitted to Physical Review
Self-calibrating d-scan: measuring ultrashort laser pulses on-target using an arbitrary pulse compressor
In most applications of ultrashort pulse lasers, temporal compressors are
used to achieve a desired pulse duration in a target or sample, and precise
temporal characterization is important. The dispersion-scan (d-scan) pulse
characterization technique usually involves using glass wedges to impart
variable, well-defined amounts of dispersion to the pulses, while measuring the
spectrum of a nonlinear signal produced by those pulses. This works very well
for broadband few-cycle pulses, but longer, narrower bandwidth pulses are much
more difficult to measure this way. Here we demonstrate the concept of
self-calibrating d-scan, which extends the applicability of the d-scan
technique to pulses of arbitrary duration, enabling their complete measurement
without prior knowledge of the introduced dispersion. In particular, we show
that the pulse compressors already employed in chirped pulse amplification
(CPA) systems can be used to simultaneously compress and measure the temporal
profile of the output pulses on-target in a simple way, without the need of
additional diagnostics or calibrations, while at the same time calibrating the
often-unknown differential dispersion of the compressor itself. We demonstrate
the technique through simulations and experiments under known conditions.
Finally, we apply it to the measurement and compression of 27.5 fs pulses from
a CPA laser.Comment: 11 pages, 5 figures, Scientific Reports, in pres
Results for Channel Error Profiles for DECT
This letter presents the main statistical characterization
of the underlying error process obtained in the case of
the Digital European Cordless Telecommunications (DECT) radio
system. By simulation of the transmission link, error sequences
are generated for different channel parameters. Relevant statistics
are then computed for the purpose of efficient channel coding
design and evaluation
"The Role of International Technological Spillovers in the Economic Growth of the OECD Countries "
This paper explores the role of imports as a mechanism of transmission of international technological spillovers and the significance of these for the growth and economic convergence of the OECD countries. For this purpose a growth model is estimated that includes amongst its determinants a measure of the stock of technological knowledge. The results reveal first that international technological spillovers transmitted through imports have had a favourable influence on the economic growth of the OECD countries, Secondly, they suggest that the capacity of countries to take advantage of those spillovers depend on their own human and R&D capital endowments..
Probing halo nucleus structure through intermediate energy elastic scattering
This work addresses the question of precisely what features of few body
models of halo nuclei are probed by elastic scattering on protons at high
centre-of-mass energies. Our treatment is based on a multiple scattering
expansion of the proton-projectile transition amplitude in a form which is well
adapted to the weakly bound cluster picture of halo nuclei. In the specific
case of Li scattering from protons at 800 MeV/u we show that because
core recoil effects are significant, scattering crosssections can not, in
general, be deduced from knowledge of the total matter density alone.
We advocate that the optical potential concept for the scattering of halo
nuclei on protons should be avoided and that the multiple scattering series for
the full transition amplitude should be used instead.Comment: 8 pages REVTeX, 1 eps figure, accepted for publication in Phys. Rev.
Spitzer/IRS investigation of MIPSGAL 24 microns compact bubbles
The MIPSGAL 24 m Galactic Plane Survey has revealed more than 400
compact-extended objects. Less than 15% of these MIPSGAL bubbles (MBs) are
known and identified as evolved stars. We present Spitzer observations of 4 MBs
obtained with the InfraRed Spectrograph to determine the origin of the mid-IR
emission. We model the mid-IR gas lines and the dust emission to infer physical
conditions within the MBs and consequently their nature. Two MBs show a
dust-poor spectrum dominated by highly ionized gas lines of [\ion{O}{4}],
[\ion{Ne}{3}], [\ion{Ne}{5}], [\ion{S}{3}] and [\ion{S}{4}]. We identify them
as planetary nebulae with a density of a few 10 and a central
white dwarf of K. The mid-IR emission of the two other MBs is
dominated by a dust continuum and lower-excitation lines. Both of them show a
central source in the near-IR (2MASS and IRAC) broadband images. The first
dust-rich MB matches a Wolf-Rayet star of K at 7.5 kpc with dust
components of and K. Its mass is about $10^{-3}\
\rm{M_\odot}10^{-6}\ \rm{M_\odot/yr}. The second
dust-rich MB has recently been suggested as a Be/B[e]/LBV candidate. The gas
lines of [\ion{Fe}{2}] as well as hot continuum components (\sim300\sim1250\sim7510^{-3}\ \rm{M_\odot}10^{-5}\ \rm{M_\odot/yr}$.Comment: accepted for publication in Ap
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