1,800 research outputs found
Spectroscopy of high-energy states of lanthanide ions
We discuss recent progress and future prospects for the analysis of the
4f5d excited states of lanthanide ions in host materials. Ab-initio
calculations for Ce in LiYF are used to estimate crystal-field and
spin-orbit parameters for the 4f and 5d configurations. We discuss the
possibility of using excited-state absorption to probe the electronic and
geometric structure of the 4f5d excited states in more detail and we
illustrate these ideas with calculations for Yb ions in SrCl
Impedance model for the polarization-dependent optical absorption of superconducting single-photon detectors
We measured the single-photon detection efficiency of NbN superconducting
single photon detectors as a function of the polarization state of the incident
light for different wavelengths in the range from 488 nm to 1550 nm. The
polarization contrast varies from ~5% at 488 nm to ~30% at 1550 nm, in good
agreement with numerical calculations. We use an optical-impedance model to
describe the absorption for polarization parallel to the wires of the detector.
For lossy NbN films, the absorption can be kept constant by keeping the product
of layer thickness and filling factor constant. As a consequence, we find that
the maximum possible absorption is independent of filling factor. By
illuminating the detector through the substrate, an absorption efficiency of
~70% can be reached for a detector on Si or GaAs, without the need for an
optical cavity.Comment: 15 pages, 5 figures, submitted to Journal of Applied Physic
Charging mechanisms in persistent phosphors
The development of novel persistent phosphors is currently hampered by a limited understanding of the charging mechanism. Using x-ray absorption and thermoluminescence spectroscopy we evaluate the validity of recently proposed models for the charging mechanism
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