19,643 research outputs found
Apparatus for precision focussing and positioning of a beam waist on a target
The invention relates to optical focussing apparatus and, more particularly, to optical apparatus for focussing a highly collimated Gaussian beam which provides independent and fine control over the focus waist diameter, the focus position both along the beam axis and transverse to the beam, and the focus angle. A beam focussing and positioning apparatus provides focussing and positioning for the waist of a waisted beam at a desired location on a target such as an optical fiber. The apparatus includes a first lens, having a focal plane f sub 1, disposed in the path of an incoming beam and a second lens, having a focal plane f sub 2 and being spaced downstream from the first lens by a distance at least equal to f sub 1 + 10 f sub 2, which cooperates with the first lens to focus the waist of the beam on the target. A rotatable optical device, disposed upstream of the first lens, adjusts the angular orientation of the beam waist. The transverse position of the first lens relative to the axis of the beam is varied to control the transverse position of the beam waist relative to the target (a fiber optic as shown) while the relative axial positions of the lenses are varied to control the diameter of the beam waist and to control the axial position of the beam waist. Mechanical controllers C sub 1, C sub 2, C sub 3, C sub 4, and C sub 5 control the elements of the optical system. How seven adjustments can be made to correctly couple a laser beam into an optical fiber is illustrated. Prior art systems employing optical techniques to couple a laser beam into an optical fiber or other target simply do not provide the seven necessary adjustments. The closest known prior art, a Newport coupler, provides only two of the seven required adjustments
Light transmission assisted by Brewster-Zennek modes in chromium films carrying a subwavelength hole array
This work confirms that not only surface plasmons but many other kinds of
electromagnetic eigenmodes should be considered in explaining the values of the
transmittivity through a slab bearing a two-dimensional periodic corrugation.
Specifically, the role of Brewster-Zennek modes appearing in metallic films
exhibiting regions of weak positive dielectric constant. It is proposed that
these modes play a significant role in the light transmission in a thin
chromium film perforated with normal cylindrical holes, for appropriate lattice
parameters.Comment: 5 pages, 4 figures. Published versio
Neutron spectroscopic factors of Ni isotopes from transfer reactions
177 neutron spectroscopic factors for nickel isotopes have been extracted by
performing a systematic analysis of the angular distributions measured from
(d,p) transfer reactions. A subset of the extracted spectroscopic factors are
compared to predictions of large-basis shell models in the full pf model space
using the GXPF1A effective interaction, and the (f5/2, p3/2, p1/2, g9/2) model
space using the JJ4PNA interaction. For ground states, the predicted
spectroscopic factors using the GXPF1A effective interaction in the full pf
model space agree very well with the experimental values, while predictions
based on several other effective interactions and model spaces are about 30%
higher than the experimental values. For low-energy excited states (<3.5 MeV),
the agreement between the extracted spectroscopic factors and shell model
calculations is not better than a factor of two.Comment: 18 pages, 4 figures, 2 tables. accepted for publication in PR
Transport Model Simulations of Projectile Fragmentation Reactions at 140 MeV/nucleon
The collisions in four different reaction systems using Ca and
Ni isotope beams and a Be target have been simulated using the Heavy
Ion Phase Space Exploration and the Antisymmetrized Molecular Dynamics models.
The present study mainly focuses on the model predictions for the excitation
energies of the hot fragments and the cross sections of the final fragments
produced in these reactions. The effects of various factors influencing the
final fragment cross sections, such as the choice of the statistical decay code
and its parameters have been explored. The predicted fragment cross sections
are compared to the projectile fragmentation cross sections measured with the
A1900 mass separator. At MeV, reaction dynamics can significantly
modify the detection efficiencies for the fragments and make them different
from the efficiencies applied to the measured data reported in the previous
work. The effects of efficiency corrections on the validation of event
generator codes are discussed in the context of the two models.Comment: 28 pages, 13 figure
The Influence of in-medium NN cross-sections, symmetry potential and impact parameter on the isospin observables
We explore the influence of in-medium nucleon-nucleon cross section, symmetry
potential and impact parameter on isospin sensitive observables in
intermediate-energy heavy-ion collisions with the ImQMD05 code, a modified
version of Quantum Molecular Dynamics model. At incident velocities above the
Fermi velocity, we find that the density dependence of symmetry potential plays
a more important role on the double neutron to proton ratio and the
isospin transport ratio than the in-medium nucleon-nucleon cross
sections, provided that the latter are constrained to a fixed total NN
collision rate. We also explore both and as a function of the
impact parameter. Since the copious production of intermediate mass fragments
is a distinguishing feature of intermediate-energy heavy-ion collisions, we
examine the isospin transport ratios constructed from different groups of
fragments. We find that the values of the isospin transport ratios for
projectile rapidity fragments with are greater than those constructed
from the entire projectile rapidity source. We believe experimental
investigations of this phenomenon can be performed. These may provide
significant tests of fragmentation time scales predicted by ImQMD calculations.Comment: 24 pages, 9 figures, to be published in Phys. Rev.
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