35,440 research outputs found
Preliminary design of the full-Stokes UV and visible spectropolarimeter for UVMag/Arago
The UVMag consortium proposed the space mission project Arago to ESA at its
M4 call. It is dedicated to the study of the dynamic 3D environment of stars
and planets. This space mission will be equipped with a high-resolution
spectropolarimeter working from 119 to 888 nm. A preliminary optical design of
the whole instrument has been prepared and is presented here. The design
consists of the telescope, the instrument itself, and the focusing optics.
Considering not only the scientific requirements, but also the cost and size
constraints to fit a M-size mission, the telescope has a 1.3 m diameter primary
mirror and is a classical Cassegrain-type telescope that allows a
polarization-free focus. The polarimeter is placed at this Cassegrain focus.
This is the key element of the mission and the most challenging to be designed.
The main challenge lies in the huge spectral range offered by the instrument;
the polarimeter has to deliver the full Stokes vector with a high precision
from the FUV (119 nm) to the NIR (888 nm). The polarimeter module is then
followed by a high-resolution echelle-spectrometer achieving a resolution of
35000 in the visible range and 25000 in the UV. The two channels are separated
after the echelle grating, allowing a specific cross-dispersion and focusing
optics for the UV and visible ranges. Considering the large field of view and
the high numerical aperture, the focusing optic for both the UV and visible
channels is a Three-Mirror-Anastigmat (TMA) telescope, in order to focus the
various wavelengths and many orders onto the detectors.Comment: 6 pages, 6 figures, IAUS 30
Quartz-based flat-crystal resonant inelastic x-ray scattering spectrometer with sub-10 meV energy resolution
Continued improvement of the energy resolution of resonant inelastic x-ray
scattering (RIXS) spectrometers is crucial for fulfilling the potential of this
technique in the study of electron dynamics in materials of fundamental and
technological importance. In particular, RIXS is the only alternative tool to
inelastic neutron scattering capable of providing fully momentum resolved
information on dynamic spin structures of magnetic materials, but is limited to
systems whose magnetic excitation energy scales are comparable to the energy
resolution. The state-of-the-art spherical diced crystal analyzer optics
provides energy resolution as good as 25 meV but has already reached its
theoretical limit. Here, we demonstrate a novel sub-10meV RIXS spectrometer
based on flat-crystal optics at the Ir-L absorption edge (11.215 keV)
that achieves an analyzer energy resolution of 3.9meV, very close to the
theoretical value of 3.7meV. In addition, the new spectrometer allows
efficient polarization analysis without loss of energy resolution. The
performance of the instrument is demonstrated using longitudinal acoustical and
optical phonons in diamond, and magnon in SrIrO. The novel
sub-10meV RIXS spectrometer thus provides a window into magnetic
materials with small energy scales
Disentangling Cooper-pair formation above Tc from the pseudogap state in the cuprates
The discovery of the pseudogap in the cuprates created significant excitement
amongst physicists as it was believed to be a signature of pairing, in some
cases well above the room temperature. In this "pre-formed pairs" scenario, the
formation of pairs without quantum phase rigidity occurs below T*. These pairs
condense and develop phase coherence only below Tc. In contrast, several recent
experiments reported that the pseudogap and superconducting states are
characterized by two different energy scales, pointing to a scenario, where the
two compete. However a number of transport, magnetic, thermodynamic and
tunneling spectroscopy experiments consistently detect a signature of
phase-fluctuating superconductivity above leaving open the question of whether
the pseudogap is caused by pair formation or not. Here we report the discovery
of a spectroscopic signature of pair formation and demonstrate that in a region
of the phase diagram commonly referred to as the "pseudogap", two distinct
states coexist: one that persists to an intermediate temperature Tpair and a
second that extends up to T*. The first state is characterized by a doping
independent scaling behavior and is due to pairing above Tc, but significantly
below T*. The second state is the "proper" pseudogap - characterized by a
"checker board" pattern in STM images, the absence of pair formation, and is
likely linked to Mott physics of pristine CuO2 planes. Tpair has a universal
value around 130-150K even for materials with very different Tc, likely setting
limit on highest, attainable Tc in cuprates. The observed universal scaling
behavior with respect to Tpair indicates a breakdown of the classical picture
of phase fluctuations in the cuprates.Comment: 9 pages, 4 figure
Shot-noise limited monitoring and phase locking of the motion of a single trapped ion
We perform high-resolution real-time read-out of the motion of a single
trapped and laser-cooled Ba ion. By using an interferometric setup we
demonstrate shot-noise limited measurement of thermal oscillations with
resolution of 4 times the standard quantum limit. We apply the real-time
monitoring for phase control of the ion motion through a feedback loop,
suppressing the photon recoil-induced phase diffusion. Due to the spectral
narrowing in phase-locked mode, the coherent ion oscillation is measured with
resolution of about 0.3 times the standard quantum limit
UVMag: Space UV and visible spectropolarimetry
UVMag is a project of a space mission equipped with a high-resolution
spectropolarimeter working in the UV and visible range. This M-size mission
will be proposed to ESA at its M4 call. The main goal of UVMag is to measure
the magnetic fields, winds and environment of all types of stars to reach a
better understanding of stellar formation and evolution and of the impact of
stellar environment on the surrounding planets. The groundbreaking combination
of UV and visible spectropolarimetric observations will allow the scientists to
study the stellar surface and its environment simultaneously. The instrumental
challenge for this mission is to design a high-resolution space
spectropolarimeter measuring the full-Stokes vector of the observed star in a
huge spectral domain from 117 nm to 870 nm. This spectral range is the main
difficulty because of the dispersion of the optical elements and of
birefringence issues in the FUV. As the instrument will be launched into space,
the polarimetric module has to be robust and therefore use if possible only
static elements. This article presents the different design possibilities for
the polarimeter at this point of the project.Comment: 9 pages, 4 figures, SPIE Conference Astronomical Telescopes +
Instrumentation Montreal June 201
Spectral pre-modulation of training examples enhances the spatial resolution of the Phase Extraction Neural Network (PhENN)
The Phase Extraction Neural Network (PhENN) is a computational architecture,
based on deep machine learning, for lens-less quantitative phase retrieval from
raw intensity data. PhENN is a deep convolutional neural network trained
through examples consisting of pairs of true phase objects and their
corresponding intensity diffraction patterns; thereafter, given a test raw
intensity pattern PhENN is capable of reconstructing the original phase object
robustly, in many cases even for objects outside the database where the
training examples were drawn from. Here, we show that the spatial frequency
content of the training examples is an important factor limiting PhENN's
spatial frequency response. For example, if the training database is relatively
sparse in high spatial frequencies, as most natural scenes are, PhENN's ability
to resolve fine spatial features in test patterns will be correspondingly
limited. To combat this issue, we propose "flattening" the power spectral
density of the training examples before presenting them to PhENN. For phase
objects following the statistics of natural scenes, we demonstrate
experimentally that the spectral pre-modulation method enhances the spatial
resolution of PhENN by a factor of 2.Comment: 12 pages, 10 figure
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