1,329 research outputs found
Femtosecond dynamics of electronic states in the Mott insulator 1T-TaS2 by time-resolved photoelectron spectroscopy
Photoexcitation of the Mott insulator 1T-TaS2 by an intense laser pulse leads to an ultrafast transition toward a gapless phase. Beside the collapse of the electronic gap, the sudden excitation of the charge density wave mode results into periodic oscillations of the electronic states. We employ time resolved photoelectron spectroscopy to monitor the rich dynamics of electrons and phonons during the relaxation toward equilibrium. The qualitative difference between the oscillatory dynamics of the charge density wave and the monotonic recovery of the electronic gap proves that 1T-TaS2 is indeed a Mott insulator. Moreover the quasi-instantaneous build up of mid gap states is in contrast with the retarded response expected from a Peierls insulating phase. Interestingly, the photoinduced electronic states in the midgap spectral region display a weak resonance that is reminiscent of a quasiparticle peak
Renormalized spin coefficients in the accumulated orbital phase for unequal mass black hole binaries
We analyze galactic black hole mergers and their emitted gravitational waves.
Such mergers have typically unequal masses with mass ratio of the order 1/10.
The emitted gravitational waves carry the inprint of spins and mass quadrupoles
of the binary components. Among these contributions, we consider here the
quasi-precessional evolution of the spins. A method of taking into account
these third post-Newtonian (3PN) effects by renormalizing (redefining) the 1.5
PN and 2PN accurate spin contributions to the accumulated orbital phase is
developed.Comment: 10 pages, to appear in Class. Quantum Grav. GWDAW13 Proceedings
Special Issue, v2: no typos conjectur
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Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas
We report on terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures, which exhibit single-mode emission at 3.360, 3.921, and 4.745 THz. These frequencies are in close correspondence to fine-structure transitions of Al atoms, N+ ions, and O atoms, respectively. Due to the low electrical pump power of these THz QCLs, they can be operated in a mechanical cryocooler in continuous-wave mode, while a sufficient intrinsic tuning range of more than 5 GHz is maintained. The single-mode operation and the intrinsic tuning range of these THz QCLs allow for the application of these lasers as radiation sources for high-resolution absorption spectroscopy to determine the absolute densities of Al atoms, N+ ions, and O atoms in plasmas
Recommended from our members
Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas
We report on terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures, which exhibit single-mode emission at 3.360, 3.921, and 4.745 THz. These frequencies are in close correspondence to fine-structure transitions of Al atoms, N+ ions, and O atoms, respectively. Due to the low electrical pump power of these THz QCLs, they can be operated in a mechanical cryocooler in continuous-wave mode, while a sufficient intrinsic tuning range of more than 5 GHz is maintained. The single-mode operation and the intrinsic tuning range of these THz QCLs allow for the application of these lasers as radiation sources for high-resolution absorption spectroscopy to determine the absolute densities of Al atoms, N+ ions, and O atoms in plasmas
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Terahertz absorption spectroscopy for measuring atomic oxygen densities in plasmas
This paper describes the first implementation of terahertz (THz) quantum cascade lasers for high-resolution absorption spectroscopy on plasmas. Absolute densities of ground state atomic oxygen were directly obtained by using the fine structure transition at approximately 4.75 THz. Measurements were performed on a low-pressure capacitively coupled radio frequency oxygen discharge. The detection limit in this arrangement was found to be 2 × 10 13 cm−3, while the measurement accuracy was within 5%, as demonstrated by reference measurements of a well-defined ammonia transition. The results show that the presented method is well suited to measure atomic oxygen densities, and it closes the THz gap for quantitative atomic density measurements in harsh environments such as plasmas
Recommended from our members
Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas
We report on terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures, which exhibit single-mode emission at 3.360, 3.921, and 4.745 THz. These frequencies are in close correspondence to fine-structure transitions of Al atoms, N+ ions, and O atoms, respectively. Due to the low electrical pump power of these THz QCLs, they can be operated in a mechanical cryocooler in continuous-wave mode, while a sufficient intrinsic tuning range of more than 5 GHz is maintained. The single-mode operation and the intrinsic tuning range of these THz QCLs allow for the application of these lasers as radiation sources for high-resolution absorption spectroscopy to determine the absolute densities of Al atoms, N+ ions, and O atoms in plasmas
Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
Gaia Early Data Release 3 (Gaia EDR3) gives trigonometric parallaxes for
nearly 1.5 billion sources. Inspection of the EDR3 data for sources identified
as quasars reveals that their parallaxes are biased, that is systematically
offset from the expected distribution around zero, by a few tens of
microarcsec. We attempt to map the main dependencies of the parallax bias in
EDR3. In principle this could provide a recipe for correcting the EDR3
parallaxes. For faint sources the quasars provide the most direct way to
estimate parallax bias. In order to extend this to brighter sources and a
broader range of colours, we use differential methods based on physical pairs
(binaries) and sources in the Large Magellanic Cloud. The functional forms of
the dependencies are explored by mapping the systematic differences between
EDR3 and DR2 parallaxes. The parallax bias is found to depend in a non-trivial
way on (at least) the magnitude, colour, and ecliptic latitude of the source.
Different dependencies apply to the five- and six-parameter solutions in EDR3.
While it is not possible to derive a definitive recipe for the parallax
correction, we give tentative expressions to be used at the researcher's
discretion and point out some possible paths towards future improvements.Comment: 32 pages, 30 figures. Submitted to Astronomy & Astrophysics. Revised
version where typos in (A.3) have been corrected. For associated code, see
https://www.cosmos.esa.int/web/gaia/edr3-code (code was not affected by the
typos
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