181 research outputs found
Influence of Phase Matching on the Cooper Minimum in Ar High Harmonic Spectra
We study the influence of phase matching on interference minima in high
harmonic spectra. We concentrate on structures in atoms due to interference of
different angular momentum channels during recombination. We use the Cooper
minimum (CM) in argon at 47 eV as a marker in the harmonic spectrum. We measure
2d harmonic spectra in argon as a function of wavelength and angular
divergence. While we identify a clear CM in the spectrum when the target gas
jet is placed after the laser focus, we find that the appearance of the CM
varies with angular divergence and can even be completely washed out when the
gas jet is placed closer to the focus. We also show that the argon CM appears
at different wavelengths in harmonic and photo-absorption spectra measured
under conditions independent of any wavelength calibration. We model the
experiment with a simulation based on coupled solutions of the time-dependent
Schr\"odinger equation and the Maxwell wave equation, including both the single
atom response and macroscopic effects of propagation. The single atom
calculations confirm that the ground state of argon can be represented by its
field free symmetry, despite the strong laser field used in high harmonic
generation. Because of this, the CM structure in the harmonic spectrum can be
described as the interference of continuum and channels, whose relative
phase jumps by at the CM energy, resulting in a minimum shifted from the
photoionization result. We also show that the full calculations reproduce the
dependence of the CM on the macroscopic conditions. We calculate simple phase
matching factors as a function of harmonic order and explain our experimental
and theoretical observation in terms of the effect of phase matching on the
shape of the harmonic spectrum. Phase matching must be taken into account to
fully understand spectral features related to HHG spectroscopy
Attosecond pulse shaping around a Cooper minimum
High harmonic generation (HHG) is used to measure the spectral phase of the
recombination dipole matrix element (RDM) in argon over a broad frequency range
that includes the 3p Cooper minimum (CM). The measured RDM phase agrees well
with predictions based on the scattering phases and amplitudes of the
interfering s- and d-channel contributions to the complementary photoionization
process. The reconstructed attosecond bursts that underlie the HHG process show
that the derivative of the RDM spectral phase, the group delay, does not have a
straight-forward interpretation as an emission time, in contrast to the usual
attochirp group delay. Instead, the rapid RDM phase variation caused by the CM
reshapes the attosecond bursts.Comment: 5 pages, 5 figure
Implementation of advanced practice nursing for minor orthopedic injuries in the emergency care context – a non-inferiority study
Aims
To evaluate the implementation of advanced practice nursing for patients with minor orthopedic injuries, including comparison of outcomes in relation to advanced practice nurse versus standard (physician-led) care models.
Design
A non-inferiority study was performed in an emergency department in Norway, where advanced practice nursing is in an initial stage of implementation. The non-inferiority design was chosen to test whether the new advanced practice nursing model does not compromise quality of care compared to the standard care model already in use.
Methods
Patients with minor orthopedic injuries were assessed and treated by either advanced practice nursing or standard (physician-led) care models. Participating patients were assigned to the professional available at presentation. In the nursing model, registered nurses worked at an advanced level/applied advanced practice nursing following in-house-training. Senior orthopedic specialists evaluated the diagnostic and treatment accuracy in both models. Data were collected in a tool developed for this study, from May to October, 2019.
Results
In total, 335 cases were included, of which 167 (49.9 %) were assessed and treated in the nursing model. Overall, correct diagnosis was found in 97.3 % (n = 326) of the cases, and correct treatment was found in 91.3 % (n = 306) of the cases. In comparison of missed diagnosis between advanced practice nurse and the standard (physician-led) care model showed inconclusive results (risk ratio: 0.29, 95% CI: 0.06-1.36). In comparison of treatment outcomes, the results showed that the advanced practice nursing model was non-inferior (risk ratio: 0.45, 95% CI: 0.21-0.97).
Conclusion
Advanced practice nursing care models can be used to diagnose and treat minor orthopedic injuries without compromising quality of care. Further implementation of the advanced practice nurse care model is encouraged
Macroscopic studies of short-pulse high-order harmonic generation using the time-dependent Schrödinger equation
We consider high harmonic generation by ultrashort (27–108 fs) laser pulses and calculate the macroscopic response of a collection of atoms to such a short pulse. We show how the harmonic spectrum after propagation through the medium is significantly different from the single-atom spectrum. We use single-atom data calculated by integration of the time-dependent Schrödinger equation and propose a method, based on an adiabatic approximation, to extract the data necessary to perform a propagation calculation. © 1998 The American Physical Society
Escape and Spreading Properties of Charge-Exchange Resonances in Bi 208
The properties of charge-exchange excitations of Pb with , i.e., the isobaric analog and Gamow-Teller resonances, are studied within
a self-consistent model making use of an effective force of the Skyrme type.
The well-known isobaric analog case is used to assess the reliability of the
model. The calculated properties of the Gamow-Teller resonance are compared
with recent experimental measurements with the aim of better understanding the
microscopic structure of this mode.Comment: 26 pages including references, figure captions and tables. Figures
are available upon request at [email protected] (decnet 32858::COLO).
Preprint code: IPNO/TH 94-2
The -Axial Exchange Current
The axial exchange current operator that arises from the coupling of the
axial field to the pion and effective scalar field in nuclei is constructed.
The spatial dependence of this exchange current operator may be determined
directly from the nucleon-nucleon interaction. This ""-axial
exchange current contributes about 5\% to the quenching of the nucleon axial
current coupling constant in heavy nuclei.Comment: 10pages, Latex fil
Wave packet retrieval by multi-photon quantum beat spectroscopy in helium
We show that we can probe the components of an attosecond bound electron wave packet by mapping the quantum beat signal produced by a synchronized delayed few-cycle infrared pulse into the continuum. In addition, spectrally overlapping peaks that result from one-, two- or three-photon processes from more or less deeply bound states can in principle be interferometrically resolved with high resolution
Direct extraction of intense-field-induced polarization in the continuum on the attosecond time scale from transient absorption
A procedure is suggested for using transient absorption spectroscopy above the ionization threshold to measure the polarization of the continuum induced by an intense optical pulse. In this way transient absorption measurement can be used to probe subfemtosecond intense field dynamics in atoms and molecules. The method is based on an approximation to the dependence of these spectra on time delay between an attosecond XUV probe pulse and an intense pump pulse that is tested over a wide range of intensities and time delays by all-electrons-active calculations using the multiconfiguration time-dependent Hartree-Fock method in the case of neon
Attosecond pulse trains generated using two color laser fields
We investigate the spectral and temporal structure of high harmonic emission from argon exposed to an infrared laser field and its second harmonic. For a wide range of generating conditions, trains of attosecond pulses with only one pulse per infrared cycle are generated. The synchronization necessary for producing such trains ensures that they have a stable pulse-to-pulse carrier envelope phase, unlike trains generated from one color fields, which have two pulses per cycle and a pi phase shift between consecutive pulses. Our experiment extends the generation of phase stabilized few cycle pulses to the extreme ultraviolet regime
Determination of the Gamow-Teller Quenching Factor from Charge Exchange Reactions on 90Zr
Double differential cross sections between 0-12 degrees were measured for the
90Zr(n,p) reaction at 293 MeV over a wide excitation energy range of 0-70 MeV.
A multipole decomposition technique was applied to the present data as well as
the previously obtained 90Zr(p,n) data to extract the Gamow-Teller (GT)
component from the continuum. The GT quenching factor Q was derived by using
the obtained total GT strengths. The result is Q=0.88+/-0.06 not including an
overall normalization uncertainty in the GT unit cross section of 16%.Comment: 11 papes, 4 figures, submitted to Physics Letters B (accepted),
gzipped tar file, changed content
- …