445 research outputs found
RGB generation by four-wave mixing in small-core holey fibers
We report the generation of white light comprising red, green, and blue spectral bands from a frequency-doubled fiber laser by an efficient four-wave mixing process in submicron-sized cores of microstructured holey fibers. A master-oscillator power amplifier (MOPA) source based on Yb-doped fiber is employed to generate 80 ps pulses at 1060 nm wavelength with 32 MHz repetition rate, which are then frequency-doubled in an LBO crystal to generate up to 2 W average power of green light. The green pump is then carefully launched into secondary cores of the cladding of photonic bandgap fibers. These secondary cores with diameters of about 400 to 800 nm act as highly nonlinear waveguides. At the output, we observe strong red and blue sidebands which, together with the remaining green pump light, form a visible white light source of about 360 mW. The generating process is identified as four-wave mixing where phase matching is achieved by birefringence in the secondary cores which arises from non-symmetric deformation during the fiber fabrication. Numerical models of the fiber structure and of the nonlinear processes confirm our interpretation. Finally, we discuss power scaling and limitations of the white light source due to the damage threshold of silica fibers
Phase sensitive amplification in a highly nonlinear lead-silicate fibre
We experimentally demonstrate phase-sensitive amplification in a highly nonlinear lead-silicate W-type fibre. A phase-sensitive gain swing of 6dB was observed in a 1.56m sample of the fibre for a total launched power of 33dBm
Phenomenological and Microscopic Optical-Model Descriptions of 99 MeV 6-Li Scattering
This work was supported by National Science Foundation Grants PHY 76-84033A01, PHY 78-22774, and Indiana Universit
Optical-Model Description of Time-Reversal Violation
A time-reversal-violating spin-correlation coefficient in the total cross
section for polarized neutrons incident on a tensor rank-2 polarized target is
calculated by assuming a time-reversal-noninvariant, parity-conserving
``five-fold" interaction in the neutron-nucleus optical potential. Results are
presented for the system for neutron incident energies
covering the range 1--20 MeV. From existing experimental bounds, a strength of
keV is deduced for the real and imaginary parts of the five-fold
term, which implies an upper bound of order on the relative -odd
strength when compared to the central real optical potential.Comment: 11 pages (Revtex
Halo Excitation of He in Inelastic and Charge-Exchange Reactions
Four-body distorted wave theory appropriate for nucleon-nucleus reactions
leading to 3-body continuum excitations of two-neutron Borromean halo nuclei is
developed. The peculiarities of the halo bound state and 3-body continuum are
fully taken into account by using the method of hyperspherical harmonics. The
procedure is applied for A=6 test-bench nuclei; thus we report detailed studies
of inclusive cross sections for inelastic He(p,p')He and
charge-exchange Li(n,p)He reactions at nucleon energy 50 MeV. The
theoretical low-energy spectra exhibit two resonance-like structures. The first
(narrow) is the excitation of the well-known three-body resonance. The
second (broad) bump is a composition of overlapping soft modes of
multipolarities whose relative weights depend on
transferred momentum and reaction type. Inelastic scattering is the most
selective tool for studying the soft dipole excitation mode.Comment: Submitted to Phys. Rev. C., 11 figures using eps
Gamow-Teller strength in 54Fe and 56Fe
Through a sequence of large scale shell model calculations, total
Gamow-Teller strengths ( and ) in Fe and Fe are
obtained. They reproduce the experimental values once the operator
is quenched by the standard factor of . Comparisons are made with recent
Shell Model Monte Carlo calculations. Results are shown to depend critically on
the interaction. From an analysis of the GT+ and GT strength functions it is
concluded that experimental evidence is consistent with the sum rule.Comment: 6 pages, RevTeX 3.0 using psfig, 7 Postscript figures included using
uufile
Nuclear Shell Model Calculations of Neutralino-Nucleus Cross Sections for Silicon 29 and Germanium 73
We present the results of detailed nuclear shell model calculations of the
spin-dependent elastic cross section for neutralinos scattering from \si29 and
\ge73. The calculations were performed in large model spaces which adequately
describe the configuration mixing in these two nuclei. As tests of the computed
nuclear wave functions, we have calculated several nuclear observables and
compared them with the measured values and found good agreement. In the limit
of zero momentum transfer, we find scattering matrix elements in agreement with
previous estimates for \si29 but significantly different than previous work for
\ge73. A modest quenching, in accord with shell model studies of other heavy
nuclei, has been included to bring agreement between the measured and
calculated values of the magnetic moment for \ge73. Even with this quenching,
the calculated scattering rate is roughly a factor of 2 higher than the best
previous estimates; without quenching, the rate is a factor of 4 higher. This
implies a higher sensitivity for germanium dark matter detectors. We also
investigate the role of finite momentum transfer upon the scattering response
for both nuclei and find that this can significantly change the expected rates.
We close with a brief discussion of the effects of some of the non-nuclear
uncertainties upon the matrix elements.Comment: 31 pages, figures avaiable on request, UCRL-JC-11408
Do Hadronic Charge Exchange Reactions Measure Electroweak L = 1 Strength?
An eikonal model has been used to assess the relationship between calculated
strengths for first forbidden beta decay and calculated cross sections for
(p,n) charge exchange reactions. It is found that these are proportional for
strong transitions, suggesting that hadronic charge exchange reactions may be
useful in determining the spin-dipole matrix elements for astrophysically
interesting leptonic transitions.Comment: 14 pages, 5 figures, Submitted to Physical Review
Nuclear spin structure in dark matter search: The finite momentum transfer limit
Spin-dependent elastic scattering of weakly interacting massive dark matter
particles (WIMP) off nuclei is reviewed. All available, within different
nuclear models, structure functions S(q) for finite momentum transfer (q>0) are
presented. These functions describe the recoil energy dependence of the
differential event rate due to the spin-dependent WIMP-nucleon interactions.
This paper, together with the previous paper ``Nuclear spin structure in dark
matter search: The zero momentum transfer limit'', completes our review of the
nuclear spin structure calculations involved in the problem of direct dark
matter search.Comment: 39 pages, 12 figures, a review in revtex
The GAPS Programme with HARPS-N@TNG IX. The multi-planet system KELT-6: detection of the planet KELT-6 c and measurement of the Rossiter-McLaughlin effect for KELT-6 b
Aims. For more than 1.5 years we monitored spectroscopically the star KELT-6
(BD+312447), known to host the transiting hot Saturn KELT-6b, because a
previously observed long-term trend in radial velocity time series suggested
the existence of an outer companion. Methods. We collected a total of 93 new
spectra with the HARPS-N and TRES spectrographs. A spectroscopic transit of
KELT-6b was observed with HARPS-N, and simultaneous photometry was obtained
with the IAC-80 telescope. Results. We proved the existence of an outer planet
with a mininum mass Msini=3.710.21 M and a
moderately eccentric orbit () of period P3.5
years. We improved the orbital solution of KELT-6b and obtained the first
measurement of the Rossiter-McLaughlin effect, showing that the planet has a
likely circular, prograde, and slightly misaligned orbit, with a projected
spin-orbit angle =3611 degrees. We improved the KELT-6b
transit ephemeris from photometry, and we provided new measurements of the
stellar parameters. KELT-6 appears as an interesting case to study the
formation and evolution of multi-planet systems.Comment: Letter, 4 figures, accepted for publication in A&A. Some language
editing and numbering of the paper series changed (from X to IX
- …