8,032 research outputs found
Optical Design and Active Optics Methods in Astronomy
Optical designs for astronomy involve implementation of active optics and
adaptive optics from X-ray to the infrared. Developments and results of active
optics methods for telescopes, spectrographs and coronagraph planet finders are
presented. The high accuracy and remarkable smoothness of surfaces generated by
active optics methods also allow elaborating new optical design types with high
aspheric and/or non-axisymmetric surfaces. Depending on the goal and
performance requested for a deformable optical surface analytical
investigations are carried out with one of the various facets of elasticity
theory: small deformation thin plate theory, large deformation thin plate
theory, shallow spherical shell theory, weakly conical shell theory. The
resulting thickness distribution and associated bending force boundaries can be
refined further with finite element analysis. Keywords: active optics, optical
design, elasticity theory, astronomical optics, diffractive optics, X-ray
optic
Dispersion and damping of multi-quantum well polaritons from resonant Brillouin scattering by folded acoustic modes
We report on confined exciton resonances of acoustic and folded acoustic
phonon light scattering in a GaAs/AlAs multi-quantum-well. Significant
variations of the line shifts and widths are observed across the resonance and
quantitatively reproduced in terms of the polariton dispersion. This high
resolution Brillouin study brings new unexpectedly detailed informations on the
polariton dynamics in confined systems
Hole-LO phonon interaction in InAs/GaAs quantum dots
We investigate the valence intraband transitions in p-doped self-assembled
InAs quantum dots using far-infrared magneto-optical technique with polarized
radiation. We show that a purely electronic model is unable to account for the
experimental data. We calculate the coupling between the mixed hole LO-phonon
states using the Fr\"ohlich Hamiltonian, from which we determine the polaron
states as well as the energies and oscillator strengths of the valence
intraband transitions. The good agreement between the experiments and
calculations provides strong evidence for the existence of hole-polarons and
demonstrates that the intraband magneto-optical transitions occur between
polaron states
Interpretations of the Accelerating Universe
It is generally argued that the present cosmological observations support the
accelerating models of the universe, as driven by the cosmological constant or
`dark energy'. We argue here that an alternative model of the universe is
possible which explains the current observations of the universe. We
demonstrate this with a reinterpretation of the magnitude-redshift relation for
Type Ia supernovae, since this was the test that gave a spurt to the current
trend in favour of the cosmological constant.Comment: 12 pages including 2 figures, minor revision, references added, a
paragraph on the interpretation of the CMB anisotropy in the QSSC added in
conclusion, general results unchanged. To appear in the October 2002 issue of
the "Publications of the Astronmical Society of the Pacific
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