6,443 research outputs found
Continuous-wave, multimilliwatt, mid-infrared source tunable across 6.4–7.5 μm based on orientation-patterned GaAs
We report a continuous-wave (cw) source of tunable mid-infrared radiation providing tens of milliwatt of output
power in the 6460–7517 nm spectral range. The source is based on difference-frequency generation (DFG) in orientation-patterned
(OP)-GaAs pumped by a Tm-fiber laser at 2010 nm and a 1064 nm-Yb-fiber-pumped cw optical
parametric oscillator. Using a 25.7-mm-long OP-GaAs crystal, we have generated up to 51.1 mW of output power at
6790 nm, with >40 mW and >20 mW across 32% and 80% of the mid-infrared tuning range, respectively, which is to
the best of our knowledge the highest tunable cw power generated in OP-GaAs in this spectral range. The DFG
output at maximum power exhibits passive power stability better than 2.3% rms over more than 1 h and a frequency
stability of 1.8 GHz over more than 1 min, in high spatial beam quality. The system and crystal performance at high
pump powers have been studiedPostprint (published version
Optical parametric generator based on orientation-patterned gallium phosphide
We report the first pulsed optical parametric generator based on Orientation-patterned Gallium Phosphide. The output is tunable from 1721-1850 nm (signal) and 2504-2787 nm (idler), providing a total output power of 18 mW.Peer ReviewedPostprint (author's final draft
Critically phase-matched Ti:sapphire-laserpumped deep-infrared femtosecond optical parametric oscillator based on CdSiP2
We report a high-repetition-rate femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on type-I critical phase-matching in CdSiP2 (CSP), pumped directly by a Ti:sapphire laser. Using angle-tuning in the CSP crystal, the OPO can be continuously tuned across 7306–8329 nm (1201–1369 cm−1) in the deep-IR. It delivers up to 18 mW of idler average power at 7306 nm and >7 mW beyond 8000 nm at 80.5 MHz repetition rate, with the spectra exhibiting bandwidths of >150 nm across the tuning range. Moreover, the signal is tunable across 1128–1150 nm in the near-infrared, providing up to 35 mW of average power in ∼266 fs pulses at 1150 nm. Both beams exhibit single-peak Gaussian distribution in TEM00 spatial profile. With an equivalent spectral brightness of ∼5.6×1020photons s−1 mm−2 sr−10.1% BW−1, this OPO represents a viable alternative to synchrotron and supercontinuum sources for deep-IR applications in spectroscopy, metrology, and medical diagnostics.Peer ReviewedPostprint (author's final draft
A large-scale survey of X-ray filaments in the Galactic Centre
We present a catalogue of 17 filamentary X-ray features located within a
68\times34 arcmin^2 view centred on the Galactic Centre region from images
taken by Chandra. These features are described by their morphological and
spectral properties. Many of the X-ray features have non-thermal spectra that
are well fitted by an absorbed power law. Of the 17 features, we find six that
have not been previously detected, four of which are outside the immediate
20\times20 arcmin^2 area centred on the Galactic Centre. Seven of the 17
identified filaments have morphological and spectral properties expected for
pulsar wind nebulae (PWNe) with X-ray luminosities of 5\times10^32 to 10^34 erg
s^-1 in the 2.0-10.0 keV band and photon indices in the range of \Gamma = 1.1
to 1.9. In one feature, we suggest the strong neutral Fe K\alpha emission line
to be a possible indicator for past activity of Sgr A*. For G359.942-0.03, a
particular filament of interest, we propose the model of a ram pressure
confined stellar wind bubble from a massive star to account for the morphology,
spectral shape and 6.7 keV He-like Fe emission detected. We also present a
piecewise spectral analysis on two features of interest, G0.13-0.11 and
G359.89-0.08, to further examine their physical interpretations. This analysis
favours the PWN scenario for these features.Comment: 12 pages, 10 figure
Coherence scale of the Kondo lattice
It is shown that the large-N approach yields two energy scales for the Kondo
lattice model. The single-impurity Kondo temperature, , signals the onset
of local singlet formation, while Fermi liquid coherence sets in only below a
lower scale, . At low conduction electron density
("exhaustion" limit), the ratio is much smaller than unity, and
is shown to depend only on and not on the Kondo coupling. The physical
meaning of these two scales is demonstrated by computing several quantities as
a function of and temperature.Comment: 4 pages, 4 eps figures. Minor changes. To appear in Phys. Rev. Let
Far Infrared Variability of Sagittarius A*: 25.5 Hours of Monitoring with
Variable emission from Sgr~A*, the luminous counterpart to the super-massive
black hole at the center of our Galaxy, arises from the innermost portions of
the accretion flow. Better characterization of the variability is important for
constraining models of the low-luminosity accretion mode powering Sgr~A*, and
could further our ability to use variable emission as a probe of the strong
gravitational potential in the vicinity of the
black hole. We use the \textit{Herschel}
Spectral and Photometric Imaging Receiver (SPIRE) to monitor Sgr~A* at
wavelengths that are difficult or impossible to observe from the ground. We
find highly significant variations at 0.25, 0.35, and 0.5 mm, with temporal
structure that is highly correlated across these wavelengths. While the
variations correspond to 1% changes in the total intensity in the
\textit{Herschel} beam containing Sgr~A*, comparison to independent,
simultaneous observations at 0.85 mm strongly supports the reality of the
variations. The lowest point in the light curves, 0.5 Jy below the
time-averaged flux density, places a lower bound on the emission of Sgr~A* at
0.25 mm, the first such constraint on the THz portion of the SED. The
variability on few hour timescales in the SPIRE light curves is similar to that
seen in historical 1.3 mm data, where the longest time series is available, but
the distribution of variations in the sub-mm do not show a tail of
large-amplitude variations seen at 1.3 mm. Simultaneous X-ray photometry from
XMM-Newton shows no significant variation within our observing period, which
may explain the lack of very large variations if X-ray and submillimeter flares
are correlated.Comment: Accepted for publication in Ap
Representing uncertainty regarding satisfaction degrees using possibility distributions
Evaluating flexible criteria on data leads to degrees of satisfaction. If a datum is uncertain, it can be uncertain to which degree it satisfies the criterion. This uncertainty can be modelled using a possibility distribution over the domain of possible degrees of satisfaction. In this work, we discuss the meaningfulness thereof by looking at the semantics of such a representation of the uncertainty. More specifically, it is shown that defuzzification of such a representation, towards usability in (multi-criteria) decision support systems, corresponds to expressing a clear attitude towards uncertainty (optimistic, pessimistic, cautious, etc.
A Model of the EGRET Source at the Galactic Center: Inverse Compton Scattering Within Sgr A East and its Halo
Continuum low-frequency radio observations of the Galactic Center reveal the
presence of two prominent radio sources, Sgr A East and its surrounding Halo,
containing non-thermal particle distributions with power-law indices around
2.5-3.3 and 2.4, respectively. The central 1-2 pc region is also a source of
intense (stellar) UV and (dust-reprocessed) far-IR radiation that bathes these
extended synchrotron-emitting structures. A recent detection of gamma-rays
(2EGJ1746-2852) from within around 1 degree of the Galactic Center by EGRET
onboard the Compton GRO shows that the emission from this environment extends
to very high energies.
We suggest that inverse Compton scatterings between the power-law electrons
inferred from the radio properties of Sgr A East and its Halo, and the UV and
IR photons from the nucleus, may account for the possibly diffuse gamma-ray
source as well. We show that both particle distributions may be contributing to
the gamma-ray emission, though their relevant strength depends on the actual
physical properties (such as the magnetic field intensity) in each source. If
this picture is correct, the high-energy source at the Galactic Center is
extended over several arcminutes, which can be tested with thenext generation
of gamma-ray and hard X-ray missions.Comment: latex, 14 pages, 3 figures (accepted for publication in ApJ
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