Muriel Thomasset

Design and performance of AERHA, a high acceptance high resolution soft x-ray spectrometer

A soft x-ray spectrometer based on the use of an elliptical focusing mirror and a plane varied line spacing grating is described. It achieves both high resolution and high overall efficiency while remaining relatively compact. The instrument is dedicated to resonant inelastic x-ray scattering studies. We set out how this optical arrangement was judged best able to guarantee performance for the 50 - 1000 eV range within achievable fabrication targets. The AERHA (adjustable energy resolution high acceptance) spectrometer operates with an effective angular acceptance between 100 and 250 μsr (energy dependent) and a resolving power well in excess of 5000 according to the Rayleigh criterion. The high angular acceptance is obtained by means of a collecting pre-mirror. Three scattering geometries are available to enable momentum dependent measurements with 135°, 90°, and 50° scattering angles. The instrument operates on the Synchrotron SOLEIL SEXTANTS beamline which serves as a high photon flux 2 × 200 μm(2) focal spot source with full polarization control.

Latest metrology results with the SOLEIL synchrotron LTP

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.

High-efficiency B 4 C/Mo 2 C alternate multilayer grating for monochromators in the photon energy range from 0.7 to 3.4 keV

An alternate multilayer (AML) grating has been prepared by coating an ion etched lamellar grating with a B4C/Mo2C multilayer (ML) having a layer thickness close to the groove depth. Such a structure behaves as a 2D synthetic crystal and can reach very high efficiencies when the Bragg condition is satisfied. This AML coated grating has been characterized at the SOLEIL Metrology and Tests Beamline between 0.7 and 1.7 keV and at the four-crystal monochromator beamline of Physikalisch-Technische Bundesanstalt (PTB) at BESSY II between 1.75 and 3.4 keV. A peak diffraction efficiency of nearly 27% was measured at 2.2 keV. The measured efficiencies are well reproduced by numerical simulations made with the electromagnetic propagation code CARPEM. Such AML gratings, paired with a matched ML mirror, constitute efficient monochromators for intermediate energy photons. They will extend the accessible energy for many applications as x-ray absorption spectroscopy or x-ray magnetic circular dichroism experiments.

A Shack-Hartmann measuring head for the two-dimensional characterization of X-ray mirrors.

The recent development of short-wavelength optics (X/EUV, synchrotrons) requires improved metrology techniques in terms of accuracy and curvature dynamic range. In this article a stitching Shack-Hartmann head dedicated to be mounted on translation stages for the characterization of X-ray mirrors is presented. The principle of the instrument is described and experimental results for an X-ray toroidal mirror are presented. Submicroradian performances can be achieved and systematic comparison with a classical long-trace profiler is presented. The accuracy and wide dynamic range of the Shack-Hartmann long-trace-profiler head allow two-dimensional characterizations of surface figure and curvature with a submillimeter spatial resolution.

Study of Micro Roughness Parameters and Growth Characteristics of NbC/Si Multilayer using Layer by Layer Power Spectral Density Analysis

Analysis of atomic force microscopy data measured over extended length scale gives an opportunity to calculate power spectral density (PSD) and in turn micro roughness parameters over large spatial frequency range. The surface PSD function can be used to calculate the layer by layer PSD in the multilayer stacks. In the present study, information obtained so is used to analyze surface/interface imperfections in the NbC/Si multilayer over wide spatial frequency range using the topographic measurements by atomic force microscopy (AFM) technique. Inputs of growth characteristic obtained so have helped to grow a good quality NbC/Si multilayer as tested using reflectivity beamline on Indus‐1 Synchrotron facility.

Technical Report: Shack-Hartmann Long Trace Profiler: A New Generation of 2D LTP

The SH-LTP uses a 30 × 30 sampling point Shack-Hartmann Wavefront Sensor (HP26 / Imagine Optic). This sensor is optimized for working wavelengths around 400 nm, and offers high performances with accuracy less than λ/1000 rms and sensitivity less than λ/5000 rms. The light source is a single-mode fiber laser diode (405 nm). Once collimated with an achromatic doublet, the light is sent on the surface under test and reflected on the sensor for analysis (Figure 1). The basic principle is the same as for the conventional LTP [1]. However, the analysis pupil size of the sensor is about 12 × 12 mm2, with a spatial resolution of 450 μm (size of the microlenses), and at each point the local slopes are measured in both directions X and Y.