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Register a new userConcept of spectrometer for resonant inelastic X-ray scattering with parallel detection in incoming and outgoing photon energies
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V.N. Strocov
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A spectrometer for resonant inelastic X-ray scattering (RIXS) is proposed where imaging and dispersion actions in two orthogonal planes are combined to deliver full two-dimensional map of RIXS intensity in one shot with parallel detection in incoming hvin and outgoing hvout photon energies. Preliminary ray-tracing simulations with a typical undulator beamline demonstrate a resolving power well above 11000 in both hvin and hvout near a photon energy of 930 eV, with a vast potential for improvement. Combining such a spectrometer - nicknamed hv2 - with an XFEL source allows efficient time-resolved RIXS experiments.
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We describe the concepts and technical realization of the high-resolution soft-X-ray beamline ADRESS operating in the energy range from 300 to 1600 eV and intended for Resonant Inelastic X-ray Scattering (RIXS) and Angle-Resolved Photoelectron Spectroscopy (ARPES). The photon source is an undulator of novel fixed-gap design where longitudinal movement of permanent magnetic arrays controls not only the light polarization (including circular and 0-180 deg rotatable linear polarizations) but also the energy without changing the gap. The beamline optics is based on the well-established scheme of plane grating monochromator (PGM) operating in collimated light. The ultimate resolving power E/dE is above 33000 at 1 keV photon energy. The choice of blazed vs lamellar gratings and optimization of their profile parameters is described. Due to glancing angles on the mirrors as well as optimized groove densities and profiles of the gratings, high photon flux is achieved up to 1.0e13 photons/s/0.01%BW at 1 keV. Ellipsoidal refocusing optics used for the RIXS endstation demagnifies the vertical spot size down to 4 um, which allows slitless operation and thus maximal transmission of the high-resolution RIXS spectrometer delivering E/dE better than 11000 at 1 keV photon energy. Apart from the beamline optics, we give an overview of the control system, describe diagnostics and software tools, and discuss strategies used for the optical alignment. An introduction to the concepts and instrumental realization of the ARPES and RIXS endstations is given.
We present design and realization of an ultra-broadband optical spectrometer capable of measuring the spectral intensity of multi-octave-spanning light sources on a single-pulse basis with a dynamic range of up to 8 orders of magnitude. The instrument is optimized for the characterization of the temporal structure of femtosecond long electron bunches by analyzing the emitted coherent transition radiation (CTR) spectra. The spectrometer operates within the spectral range of 250nm to 11.35$mu$m, corresponding to 5.5 optical octaves. This is achieved by dividing the signal beam into three spectral groups, each analyzed by a dedicated spectrometer and detector unit. The complete instrument was characterized with regard to wavelength, relative spectral sensitivity, and absolute photo-metric sensitivity, always accounting for the light polarization and comparing different calibration methods. Finally, the capability of the spectrometer is demonstrated with a CTR measurement of a laser wakefield accelerated electron bunch, enabling to determine temporal pulse structures at unprecedented resolution.
In order to carry out inelastic X-ray scattering (IXS) experiment at BL15U1 beamline of Shanghai Synchrotron Radiation Facility (SSRF), the data acquisition and control system based on SPEC software has been developed. The IXS experimental method needs linkage control of monochromator, silicon drift detector (SDD) and ionization chamber on continuous segment-scan mode with variable step size, and gains the data of energy, spectrum and light intensity synchronously. A method is presented for achieving this function which was not realized only by using SSCAN of Experimental Physics and Industrial Control System (EPICS). This paper shows work details including control system description, SPEC configurations for EPICS devices, macro definitions and applications in the BL15U1. An IXS experiment was executed by using the SPEC control system, its results prove that the method is feasible to perform the experiment.
We report a search for photon-photon elastic scattering in vacuum in the X-ray region at an energy in the center of mass system of omega_{cms} =6.5 keV for which the QED cross section is sigma_{QED} =2.5 times 10^{-47} m^2. An X-ray beam provided by the SACLA X-ray Free Electron Laser is split and the two beamlets are made to collide at right angle, with a total integrated luminosity of (1.24 pm 0.08) times 10^{28} m^{-2}. No signal X rays from the elastic scattering that satisfy the correlation between energy and scattering angle were detected. We obtain a 95% C.L. upper limit for the scattering cross section of 1.9 times 10^{-27} m^2 at omega_{cms}=6.5 keV. The upper limit is the lowest upper limit obtained so far by keV experiments.
The resolution function of a spectrometer based on a strongly bent single crystal (bending radius of 10 cm or less) is evaluated. It is shown that the resolution is controlled by two parameters, (i) the ratio of the lattice spacing of the chosen reflection to the crystal thickness and (ii) a single parameter comprising crystal thickness, its bending radius, and anisotropic elastic constants of the chosen crystal. Diamond, due to its unique elastic properties, can provide notably higher resolution than silicon. The results allow to optimize the parameters of bent crystal spectrometers for the hard X-ray free electron laser sources.
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