58 research outputs found
On a general analytical formula for U_q(su(3))-Clebsch-Gordan coefficients
We present the projection operator method in combination with the
Wigner-Racah calculus of the subalgebra U_q(su(2)) for calculation of
Clebsch-Gordan coefficients (CGCs) of the quantum algebra U_q(su(3)). The key
formulas of the method are couplings of the tensor and projection operators and
also a tensor form for the projection operator of U_q(su(3)). We obtain a very
compact general analytical formula for the U_q(su(3)) CGCs in terms of the
U_q(su(2)) Wigner 3nj-symbols.Comment: 9 pages, LaTeX; to be published in Yad. Fiz. (Phys. Atomic Nuclei),
(2001
Mid-infrared laser filaments in the atmosphere
Filamentation of ultrashort laser pulses in the atmosphere offers unique
opportunities for long-range transmission of high-power laser radiation and
standoff detection. With the critical power of self-focusing scaling as the
laser wavelength squared, the quest for longer-wavelength drivers, which would
radically increase the peak power and, hence, the laser energy in a single
filament, has been ongoing over two decades, during which time the available
laser sources limited filamentation experiments in the atmosphere to the
near-infrared and visible ranges. Here, we demonstrate filamentation of
ultrashort mid-infrared pulses in the atmosphere for the first time. We show
that, with the spectrum of a femtosecond laser driver centered at 3.9 um, right
at the edge of the atmospheric transmission window, radiation energies above 20
mJ and peak powers in excess of 200 GW can be transmitted through the
atmosphere in a single filament. Our studies reveal unique properties of
mid-infrared filaments, where the generation of powerful mid-infrared
supercontinuum is accompanied by unusual scenarios of optical harmonic
generation, giving rise to remarkably broad radiation spectra, stretching from
the visible to the mid-infrared
Symmetry as a source of hidden coherent structures in quantum physics: general outlook and examples
A general algebraic approach, incorporating both invariance groups and
dynamic symmetry algebras, is developed to reveal hidden coherent structures
(closed complexes and configurations) in quantum many-body physics models due
to symmetries of their Hamiltonians . Its general ideas are manifested on
some recent new examples: 1) G-invariant bi-photons and a related
SU(2)-invariant treatment of unpolarized light; 2) quasi-spin clusters in
nonlinear models of quantum optics; 3) construction of composite particles and
(para)fields from G-invariant clusters due to internal symmetries.Comment: 10 pages, LATEX; Proceedings of VIII Int. Conf. on Symmetry Methods
in Physics (Dubna, July 28-August 2, 1997
Observations of the pulsating subdwarf B star Feige 48: Constraints on evolution and companions
Since pulsating subdwarf B (sdBV or EC14026) stars were first discovered
(Kilkenny et al, 1997), observational efforts have tried to realize their
potential for constraining the interior physics of extreme horizontal branch
(EHB) stars. Difficulties encountered along the way include uncertain mode
identifications and a lack of stable pulsation mode properties. Here we report
on Feige 48, an sdBV star for which follow-up observations have been obtained
spanning more than four years, which shows some stable pulsation modes.
We resolve the temporal spectrum into five stable pulsation periods in the
range 340 to 380 seconds with amplitudes less than 1%, and two additional
periods that appear in one dataset each. The three largest amplitude
periodicities are nearly equally spaced, and we explore the consequences of
identifying them as a rotationally split l=1 triplet by consulting with a
representative stellar model.
The general stability of the pulsation amplitudes and phases allows us to use
the pulsation phases to constrain the timescale of evolution for this sdBV
star. Additionally, we are able to place interesting limits on any stellar or
planetary companion to Feige 48.Comment: accepted for publication in MNRA
Multi-millijoule few-cycle mid-infrared pulses through nonlinear self-compression in bulk
The physics of strong-field applications requires driver laser pulses that are both energetic and extremely short. Whereas optical amplifiers, laser and parametric, boost the energy, their gain bandwidth restricts the attainable pulse duration, requiring additional nonlinear spectral broadening to enable few or even single cycle compression and a corresponding peak power increase. Here we demonstrate, in the mid-infrared wavelength range that is important for scaling the ponderomotive energy in strong-field interactions, a simple energy-efficient and scalable soliton-like pulse compression in a mm-long yttrium aluminium garnet crystal with no additional dispersion management. Sub-three-cycle pulses with >0.44 TW peak power are compressed and extracted before the onset of modulation instability and multiple filamentation as a result of a favourable interplay between strong anomalous dispersion and optical nonlinearity around the wavelength of 3.9 μm. As a manifestation of the increased peak power, we show the evidence of mid-infrared pulse filamentation in atmospheric air
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