Andrey Sokolov

The at-wavelength metrology facility for UV- and XUV-reflection and diffraction optics at BESSY-II

A new optics beamline and a versatile 11-axes UHV-reflectometer for at-wavelength characterization of real life-sized UV- and XUV-reflection gratings and other (nano-) optical elements has been set up and is in operation at BESSY-II. Azimuthal rotation of samples allows for reflectometry and polarimetry measurements in s- and p-polarization.

An XUV optics beamline at BESSY II

The design for a new XUV-Optics Beamline is presented. The collimated plane grating monochromator (PGM-) beamline at a bending magnet is setup at the BESSY-II synchrotron radiation facility within the framework of the blazed-grating production facility. Coupled to a versatile four-circle (ten axes) UHV- reflectometer as a permanent end station the whole setup is dedicated to at-wavelength characterization and calibration of the in-house produced precision gratings and novel nano-optical devices as well as mirrors, multilayered systems etc. It is also open to external projects employing reflectometry, spectroscopy or scattering techniques. According to its purpose, this beamline has specific features, such as: very high spectral purity, provided by two independent high order suppression systems, an advanced aperture system for suppression of stray light and scattered radiation, a broad energy range between 10 eV and 2000 eV, small beam divergence and spot size on the sample. Thus this Optics Beamline will become a powerful metrology tool for reflectivity measurements in s- or p-polarisation geometry with linearly or elliptically polarized light on real optics up to 360 mm length and 4 kg weight.

Highly efficient blazed grating with multilayer coating for tender X-ray energies

For photon energies of 1 - 5 keV, blazed gratings with multilayer coating are ideally suited for the suppression of stray and higher orders light in grating monochromators. We developed and characterized a blazed 2000 lines/mm grating coated with a 20 period Cr/C- multilayer. The multilayer d-spacing of 7.3 nm has been adapted to the line distance of 500 nm and the blaze angle of 0.84° in order to provide highest efficiency in the photon energy range between 1.5 keV and 3 keV. Efficiency of the multilayer grating as well as the reflectance of a witness multilayer which were coated simultaneously have been measured. An efficiency of 35% was measured at 2 keV while a maximum efficiency of 55% was achieved at 4 keV. In addition, a strong suppression of higher orders was observed which makes blazed multilayer gratings a favorable dispersing element also for the low X-ray energy range.

At-wavelength metrology facility for soft X-ray reflection optics.

A new Optics Beamline coupled to a versatile UHV reflectometer is successfully operating at BESSY-II. It is used to carry out at-wavelength characterization and calibration of in-house produced gratings and novel nano-optical devices as well as mirrors and multilayer systems in the UV and XUV spectral region. This paper presents most recent commissioning data of the beamline and shows their correlation with initial beamline design calculations. Special attention is paid to beamline key parameters which determine the quality of the measurements such as high-order suppression and stray light behavior. The facility is open to user operation.

Reflection zone plate wavelength-dispersive spectrometer for ultra-light elements measurements.

We have developed an electron beam excitation ultra-soft X-ray add-on device for a scanning electron microscope with a reflective zone plate mulichannel spectrometer in order to analyse ultra-light elements such as Li and B. This spectrometer has high (λ/Δλ~100) resolving power in the energy range of 45 eV - 1120 eV. Metallic Li samples were examined and fluorescence spectra successfully measured. Energy resolution of 0.49 eV was measured in the ultra-low energy range using the Al L(2,3) line at 71 eV. High sensitivity of Boron detection was demonstrated on a B(4)C sample with layer thicknesses of 1-50 nm, detecting an amount of metallic Boron as small as ~0.57 fg.

A reflectometer for at-wavelength characterization of XUV-reflection gratings

Within our technology center for production of highly efficient precision gratings a versatile 4-circle UHV-reflectometer for synchrotron radiation based at-wavelength characterization has been fabricated. The main feature is the possibility to incorporate real live-sized gratings. The samples are adjustable within six degrees of freedom by a novel UHV-tripod system, and the reflectivity can be measured at all incidence angles for both s- and p-polarization geometry. The reflectometer has been setup in a clean room hutch and it is coupled permanently to the optics beamline PM-1 for the UV and XUV range with the polarization adjustable to either linear or elliptical. The setup will be open to users by the end of 2014.

Gratings for synchrotron and FEL beamlines: a project for the manufacture of ultra-precise gratings at Helmholtz Zentrum Berlin

Establishing a facility for the production of gratings for synchrotron and free-electron laser applications is reported.

Effect of reflection and refraction on NEXAFS spectra measured in TEY mode

A study of the effect of reflection and refraction processes on the evolution of the total-electron-yield spectrum over a wide range of incidence angles including grazing angles is reported.

Inverted VLS Spectrometer at BESSY for Molecular Potential Energy Surfaces and Excitations

20 Vol. 31, No. 2, 2018, Synchrotron radiation newS Introduction In chemistry, active sites are typically centered at specific functional groups interacting with, e.g., the molecular backbone or the solvent environment. Selectivity and rate are governed by dynamic pathways on the potential energy surfaces of products, educts, and intermediaries. Thus, detailed information on the potential energy surfaces around active atomic centers holds the key to rate and selectivity. Resonant inelastic X-ray scattering (RIXS) allows us to gain this insight, since it accesses, next to electronic and vibronic excitations, spectral losses of purely structural excitations [1]. Through the transient structural distortion in the core excited state, vibrational and rotational RIXS losses are induced and the ground-state potential energy surface is described at selected atomic sites [2–6]. The RIXS spectrum is multidimensional, with not only the energy of the incident and scattered photons as coordinates, but also the polarization state and scattering angle [7]; polarization of the incident radiation gives rise to angular anisotropy of the scattering, which can be exploited to gain information about orbital symmetries in molecules [8]. RIXS is a sub-natural linewidth method with stringent symmetry selection rules, which can even be sharpened upon detuning [9] and can be interpreted in the framework of the apparent “scattering duration time” [10]. With the dedicated Momentum and Energy TRansfer RIXS (METRIXS) instrument for molecular science at BESSY, this approach becomes widely applicable for molecules. For ultrafast reactions, we will approach ultimately the transform limit in energy and time at the upcoming hRIXS at the European XFEL.

Efficient high-order suppression system for a metrology beamline

An efficient high-order suppression system has been developed and included in the optics beamline in BESSY-II synchrotron sources. The design of the instrument and its performance in suppressing high-order diffraction from the monochromator grating are described in this paper.