Since the discovery of high-Tc superconductors, understanding Mott insulating phases and their insulator to metal transitions has become increasingly important . As opposed to the Mott-insulating ground state found in 3d-electron compounds, a metallic ground state is expected to be found in strontium iridates, due to the extended 5d electronic orbitals of the Ir ions. However Sr2IrO4, shows a non metallic behavior. Its insulating ground state arises mainly from the cooperative action of the onsite Coulomb interaction and strong spin-orbit coupling, leading to a novel Jeff=1/2 Mott-insulating ground state .While the insulating ground state of Sr2IrO4 below TN = 240K is stabilized by a Mott-Slatter mecanism, the origin of the high temperature insulating ground state remains under controversy. The presence of magnetic fluctuations may also give rise to a possibly Mott-Slatter hybrid scenario in which pseudo-spins long range correlations may cooperate with spin-orbit and onsite Coulomb interaction[5-6].
A possible way to disentangle magnetic fluctuations effects from Mott physics signatures is realized by photo-exciting strontium iridate single crystals with femtosecond light pulses. Following this approach, earlier pump-probe studies [7,8] have pointed out strong similarities between iridates and cuprates electron dynamics such as a two-time scale dynamics along with the formation of in-gap states. In order to uncover short time (< 100fs) electron dynamics we present a combined super-continuum based time resolved reflectivity along with a HHG based time resolved photoemission study of Sr2IrO4 at room temperature. Our data reveal for the first time, crucial information about the time and energy resolved dynamics of the short lived in-gap states forming in the first 50fs after the photo-excitation. The origin of these in-gap states seems to be consistent with the framework of photo-doping of Mott insulators in which a photo-induced Mott gap renormalization occur.
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One direction towards compact Free Electron Laser is to replace the conventional linac by a laser plasma driven beam, provided proper electron beam manipulation to handle the large values of the energy spread and of the divergence. Applying seeding techniques enable also to reduce the required undulator length. The rapidly developing LWFA are already able to generate synchrotron radiation. With an electron divergence of typically 1 mrad and an energy spread of the order of 1 % (or few), an adequate beam manipulation through the transport to the undulator is needed for FEL amplification. Electron beam transfer follows different steps with strong focusing variable strength permanent magnet quadrupoles, an energy demixing chicane with conventional dipoles, a second set of quadrupoles for further dedicated focusing in the undulator. A test experiment for the demonstration of FEL amplification with a LWFA is under preparation and progress on the equipment preparation and expected performance are described.
The design and implementation of a pair of 100 mm-long grazing-incidence total-reflection mirrors for the hard
X-ray beamline Nanoscopium at Synchrotron Soleil is presented. A vertically and horizontally nanofocusing
mirror pair, oriented in Kirkpatrick-Baez geometry, has been designed and fabricated with the aim of creating a
diffraction-limited high-intensity 5 − 20 keV beam with a focal spot size as small as 50 nm. We describe the design
considerations, including wave-optical calculations of figures-of-merit that are relevant for spectromicroscopy,
such as the focal spot size, depth of field and integrated intensity. The mechanical positioning tolerance in the
pitch angle that is required to avoid introducing high-intensity features in the neighborhood of the focal spot
is demonstrated with simulations to be of the order of microradians, becoming tighter for shorter focal lengths
and therefore directly affecting all nanoprobe mirror systems. Metrology results for the completed mirrors are
presented, showing that better than 1.5 °A-rms figure error has been achieved over the full mirror lengths with
respect to the designed elliptical surfaces, with less than 60 nrad-rms slope errors.
The Nanoscopium 155 m-long scanning nanoprobe beamline of Synchrotron Soleil (St Aubin, France) is dedicated to
quantitative multi-modal imaging. Dedicated experimental stations, working in consecutive operation mode, will provide
coherent scatter imaging and spectro-microscopy techniques in the 5-20 keV energy range for various user communities.
Next to fast scanning, cryogenic cooling will reduce the radiation damage of sensitive samples during the measurements.
Nanoscopium is in the construction phase, the first user experiments are expected in 2014. The main characteristics of
the beamline and an overview of its status are given in this contribution.
Generalization of specific optical metrology and systematic testing of all delivered components has yield in the last
decade to a significant improvement of the optical surfaces installed on synchrotron radiation (SR) beamlines around the
world. Surface roughness is classically characterized by phase-shift interferential microscope, sometimes AFM. Long
trace profiler (LTP)1, which measures the local slope along a line profile, has been the choice instrument to measure
figure errors of large size components. Present LTPs have accuracy around 0.2 μrad RMS, and a spatial resolution
around 1 mm, but they cannot provide 2D measurement nor access the small radii that modern sagitally focusing SR
optics calls for. Stiching interferometry or Shack-Hartmann methods are good candidate for 2D measurement of figure
errors. With increasing quality of mirrors and increasing coherence of synchrotron sources the simple specification of
surface figure by the RMS slope errors of low spatial frequencies and roughness by the standard deviation of the high
frequency surface height fluctuation is becoming less and less relevant. In order to achieve given performances the
properties of an optical surface are better specified by the power spectrum of the surface errors in different spatial
frequency ranges, the definition of which depends on the actual use of the surface. Evaluating the quality of SR mirrors
used to form micro or nano X-ray probes should be checked by modeling the point spread function. It requires an
accurate measure of the surface shape in the low frequency range. The next step of SR optics improvement will come
from local polishing techniques guided by metrology. The required level of accuracy is calling for a panel of measuring
methods adapted to different spatial frequency that are still under development.
In this article, a stitching Shack-Hartmann profilometric head is presented. This instrument has been developed to answer
improved needs for surface metrology in the domain of short-wavelength optics (X/EUV). It is composed of a highaccuracy
Shack-Hartmann wavefront sensor and an illumination platform. This profilometric head is mounted on a
translation stage to perform bidimensional mappings by stitching together successive sub-aperture acquisitions. This
method ensures the submicroradian accuracy of the system and allows the user to measure large surfaces with a submillimetric
We particularly emphasize on the calibration method of the head; this method is validated by characterizing a super-flat
reference mirror. Cross-checked tests with the Soleil's long-trace profiler are also performed. The high precision of
profilometric head has been validated with the characterization of a spherical mirror. We also emphasize on the large
curvature dynamic range of the instrument with the measurement of an X-ray toric mirror.
The instrument, which performs a complete diagnostic of the surface or wavefront under test, finds its main applications
in metrology (measurement of large optics/wafers, post-polishing control and local surface finishing for the industry,
spatial quality control of laser beam).
SOLEIL Long Trace Profiler (LTP) is a custom made instrument developed in the former LURE. As many instruments of its kind, it is based on pencil beam interferometry and uses the principle of stabilisation of the probe beam by a pentaprism equivalent reflector. The interferometer however is a polarization interferometer located close to the surface under test. The optics head can be configured to measure the optics in its working position: face up, face down or sideways. Particular care is given to absolute calibration because the precise knowledge of radii of curvature is required to determine the grazing angle and align accurately the synchrotron beamlines. A reproducible calibration procedure has been defined and checked against various reference surfaces. The main limitation to accuracy is the beam instability due to aur turbulence and thermal drifts. Careful confinement, oversampled acquisitions, and data averaging can minimize this effect. Noise is not uniformly distributed over spatial frequencies. In order to better understand the influence of beam footprint on the surface under test, and the characteristics of the beam fluctuation, we have constructed a special head where two measurements, one with a narrow pencil beam and interferometric detection and another with a large unmodulated beam and centroid detection, can be done simultaneously. The first results obtained from this device are presented here.
Infrared microspectrometry, using a synchrotron radiation source, has been developed at Super-ACO (LURE-France). In order to accommodate for constrained horizontal (45 mrad) and vertical (18 mrad) collection angles, a particular care has been devoted to the design and making of the extraction optics, in order to achieve the highest brightness as possible, for small area illumination. Experimentally, a net gain of one hundred in Signal to Noise Ratio has been measured for an upper aperture of 3 X 3 micrometers 2. Several applications are currently underway, and some of them, related to Biomedical Science are reported in this paper.
We have developed a LURE a code to predict the efficiency of gratings. The code is based on differential theory and uses a simplified R-matrix propagation algorithm to obtain numerical stability on the whole range from visible to hard x-rays. Experimental and numerical studies have been performed on some test cases at a synchrotron source. A good agreement between numerical prediction and measurements has been found. The code is a rigorous application of electromagnetic theory and gives exact results as long as accurate optical constants can be attributed to grating materials. Such rigorous calculations provide an important tool for the optical engineering of modern synchrotron monochromator gratings. We give an example of application of this code to the engineering of a modern beam line and for the optimization of harmonic rejection.
A new instrumentation program was decided in 1996 to renew LURE's aging beamline equipment, and also get some experience in view of a new French synchrotron source. For the VUV and soft X-ray domain which are covered by the low energy machine Super-ACO, three new beamlines were scheduled over a three year period with a clear goal toward resolution. Two soft X-ray beamlines are equipped with grazing incidence monochromators, a spherical grating monochromator (SGM) and a plane grating monochromator; a VUV beamline will use an off-plane Eagle normal incidence monochromator. The particular features of each beamline are described. Some emphasis is given to the design, construction and alignment principles which have been followed to the insure an optical quality. A status of the program advance is given. Results from the already commissioned SGM beamline are reported.
The achievement of high resolving power from VUV to soft X-rays is a new challenge for synchrotron radiation beam-lines. When the X-UV range has to be privileged, we show that an optimized Plane
grating monochromator (PGM), which can be corrected up to large aperture angles, offer a good compromise between resolution, flux and easiness of use. The design method and especially the determination of deviation angles and gratings parameters are outlined. The dependence of ultimate performances on the fabrication accuracy is evaluated; This design is compared to an alternative SGM design and their performances are found complementary.
Though optimization softwares are commonly used in visible optical design, none seems to exist for soft x-ray optics. It is shown here that optimization techniques can be applied with some advantages to X-UV monochromator design. A merit function, suitable for minimizing the aberrations is proposed, and the general method of computation is described. Samples of the software inputs and outputs are presented, and compared to reference data. As an example of application to soft X-ray monochromator design, the optimization of the soft X-ray monochromator of the ESRF microscopy beamline is presented. Good agreement between the predicted resolution of a modified PGM monochromator and experimental measurements is reported.
In-line holography is attractive for x-ray microscopy due to its recording simplicity. A drawback of this method is the superposition of the virtual and real images, in which structures and details can be modified or lost. This superposition effectively limits the application of in-line holography to x-ray microscopy. We present in this work an iterative constrained algorithm for twin image elimination from Gabor holograms of finite support objects. It is based in the different spatial extent of both images, together with a finite support constraint. The conditions under which the algorithm is applicable are presented, together with an alternative Monte Carlo method for holograms of complex objects recorded in the shadow regions.