825 research outputs found
Photoionization cross section calculations for the halogen-like ions Kr and Xe
Photoionization cross sections calculations on the halogen-like ions; Kr
and Xe have been performed for a photon energy range from each ion
threshold to 15 eV, using large-scale close-coupling calculations within the
Dirac-Coulomb R-matrix approximation. The results from our theoretical work are
compared with recent measurements made at the ASTRID merged-beam set-up at the
University of Aarhus in Denmark and from the Fourier transform ion cyclotron
resonance (FT-ICR) trap method at the SOLEIL synchrotron radiation facility in
Saint-Aubin, France and the Advanced Light Soure (ALS). For each of these
complex ions our theoretical cross section results over the photon energy range
investigated are seen to be in excellent agreement with experiment. Resonance
energy positions and quantum defects of the prominent Rydberg resonances series
identified in the spectra are compared with experiment for these complex
halogen like-ions.Comment: Accepted for publicatio
Photoionization of Co and electron-impact excitation of Co using the Dirac R-matrix method
Modelling of massive stars and supernovae (SNe) plays a crucial role in
understanding galaxies. From this modelling we can derive fundamental
constraints on stellar evolution, mass-loss processes, mixing, and the products
of nucleosynthesis. Proper account must be taken of all important processes
that populate and depopulate the levels (collisional excitation, de-excitation,
ionization, recombination, photoionization, bound-bound processes). For the
analysis of Type Ia SNe and core collapse SNe (Types Ib, Ic and II) Fe group
elements are particularly important. Unfortunately little data is currently
available and most noticeably absent are the photoionization cross-sections for
the Fe-peaks which have high abundances in SNe. Important interactions for both
photoionization and electron-impact excitation are calculated using the
relativistic Dirac Atomic -matrix Codes (DARC) for low ionization stages of
cobalt. All results are calculated up to photon energies of 45 eV and electron
energies up to 20 eV. The wavefunction representation of Co III has been
generated using GRASP0 by including the dominant 3d, 3d[4s, 4p],
3p3d and 3p3d configurations, resulting in 292 fine structure
levels. Electron-impact collision strengths and Maxwellian averaged effective
collision strengths across a wide range of astrophysically relevant
temperatures are computed for Co III. In addition, statistically weighted
level-resolved ground and metastable photoionization cross-sections are
presented for Co II and compared directly with existing work.Comment: 11 pages, 8 figures and 4 table
Injection locking of two frequency-doubled lasers with 3.2 GHz offset for driving Raman transitions with low photon scattering in Ca
We describe the injection locking of two infrared (794 nm) laser diodes which
are each part of a frequency-doubled laser system. An acousto-optic modulator
(AOM) in the injection path gives an offset of 1.6 GHz between the lasers for
driving Raman transitions between states in the hyperfine split (by 3.2 GHz)
ground level of Ca. The offset can be disabled for use in
Ca. We measure the relative linewidth of the frequency-doubled beams
to be 42 mHz in an optical heterodyne measurement. The use of both injection
locking and frequency doubling combines spectral purity with high optical
power. Our scheme is applicable for providing Raman beams across other ion
species and neutral atoms where coherent optical manipulation is required.Comment: 3 pages, 3 figure
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