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Nanometer-Scale and Low-Density Imaging with Extreme Ultraviolet and Soft X-ray Radiation
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
The mirrors for FEL optical cavities operating in the EUV and SXR ranges have very low reflectivity. This problem can be eliminated by the employment of very long undulators (i.e., 100 m in length range for λ = 0.1 nm) and high-electron beam density for ensuring a sufficient gain. The undulators are specially designed configurations of alternatively polarized magnetic fields, in which electron bunches are traveling through an undulator on an oscillating path in a way that the radiation they emit can interact with themselves. The radiation, spontaneously emitted by the wiggling electrons, is amplified later during the passage of the electron bunches through the undulator, generating short, monochromatic light pulses. Thus, the principle of operation of FEL in the EUV and SXR region is based on “self-amplified spontaneous emission” (SASE) technique, which, on one hand, eliminates low reflectivity mirrors but, on the other hand, requires a very high-quality electron beam and a long undulator [50] (Figure 7.6).
Synchrotron Radiation X-ray Sources for Radiography and Tomography
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
Giorgio Margaritondo, Fauzia Albertin
An undulator (Figure 8.2) is a periodic series of magnets inserted along an otherwise straight portion of the closed trajectory of the electrons. The Lorentz force caused by the magnets forces the electrons to oscillate in the transverse direction, typically on the plane of the storage ring. Such oscillations correspond to an acceleration and therefore cause the emission of synchrotron light waves.
Attosecond Laser Generation
Published in Hitendra K. Malik, Laser-Matter Interaction for Radiation and Energy, 2021
SASE is a process with FEL in which a high-energy electron beam is used to create a laser beam. In the SASE process, an electron bunch with uniform density distribution and having velocity comparable to speed of light is injected into an undulator. The undulator is a periodic arrangement of the magnetic dipoles. These can be superconducting magnets or permanent magnets. Along the length of the undulator, the static magnetic field is alternating with a wavelength λμ. When electrons traverse in the undulator, they are forced to oscillate and radiate energy within a certain energy bandwidth. The emitted photons having velocities slightly greater than the electrons interact with the electrons in each undulator period. The electron bunch oscillating through the undulator is interacting with its owned created electromagnetic field through the spontaneous emission. Based on the phase differences among radiation and the electrons' oscillation, the electrons will accelerate or decelerate. The electrons in phase with the radiation will lose their energy and decelerate, whereas the electrons that are out of phase with the radiations will gain energy and hence accelerate. Because of such interactions, a longitudinal fine structure called micro-bunching is formed, which in turn, amplifies the electromagnetic field. The modulated electron bunch loses its kinetic energy to amplify certain photon energies until the time the system undergoes saturation. The energy spectra of SASE has a noise-like distribution with intense spikes. The phase space volume, which is available to the photons, is decreased by the micro-bunching; therefore, most likely, they preferred to have a similar phase and the emission of the beam is quasi-coherent. The schematic representation of the SASE mechanism of X-ray FEL is depicted in the upper part of Figure 9.2.
Ultraviolet photoabsorption in the B 3Σ- − X 3Σ- and C 3Π − X 3Σ- band systems of SO sulphur isotopologues
Published in Molecular Physics, 2022
A. N. Heays, G. Stark, J. R. Lyons, N. de Oliveira, B. R. Lewis, S. T. Gibson
Photoabsorption measurements were performed on the high-resolution absorption spectroscopy branch of the DESIRS beamline [38] at the SOLEIL synchrotron. This facility was used in similar studies of the OH and S2 radicals [39,40]. The beamline undulator generates continuum bandpass radiation with a width of 7% of its central frequency. Four overlapping measurements were required for complete coverage of the 43,000–52,000 cm−1 target region. The continuum radiation was passed through a rare-gas-filled chamber to filter unwanted higher harmonics generated in the undulator, then an absorption cell, and terminated at a vacuum-ultraviolet Fourier-transform spectrometer [41,42]. This is an all-reflection wave-front-division interferometer reliant on spatial coherence of the synchrotron beam and a modified Fresnel bi-mirror configuration with the optical-path difference scanned by translating one reflector. The instrument was operated with spectral resolution between 0.15 and 0.86 cm full-width at half-maximum (FWHM) depending on the perceived sharpness of SO features in each undulator bandpass and signal-to-noise considerations.
Characterisation of the first electronically excited state of protonated acetylene C2H3 + by coincident imaging photoelectron spectroscopy
Published in Molecular Physics, 2021
Gustavo A. Garcia, Jean-Christophe Loison, Fabian Holzmeier, Bérenger Gans, Christian Alcaraz, Laurent Nahon, Xiangkun Wu, Xiaoguo Zhou, Andras Bodi, Patrick Hemberger
Experiments were performed at the variable polarisation undulator-based beamline DESIRS [32], on the molecular beam endstation SAPHIRS [34]. The radical production scheme and its coupling to the SAPHIRS endstation has been described previously in detail [35]. In this work, F atoms (few 1013 atoms cm−3) were produced in a microwave discharge of a 5% mixture of F2 in He (Air Liquide) and fed into a quartz flow-tube reactor through a sidearm, while the precursor was diluted in He and entered the reactor via a moveable injector. The injector-nozzle distance was adjusted to deliver a reaction time of about 1 msec. The total pressure of the flow-tube reactor was maintained at 1–2 Torr. Two precursors were used to produce the C2H3 radical, the first and most obvious being ethene (99.95%, Air Liquide) through a single-H abstraction: C2H4 + F → C2H3 + HF ( kJ mol−1 [36]). This reaction was used to obtain the data in the photon energy range 8.0–10.3 eV containing the ground state of the C2v straight-Y and bridge shaped cations.
Conceptual design of a simple small angle X-ray scattering (SAXS) beamline
Published in Instrumentation Science & Technology, 2021
Zhihong Li, Quanjie Jia, Ming Li
A classic planar in-air undulator (IAU25) as the insertion device[6] is chosen as the light source of the beamline. The basic parameters and performance of the undulator are shown in Table 2 and Table S1, Figures S1, and S2 in the supplementary material. The undulator is optimized to provide fundamental radiation at 12 keV but may span the routine energy range from 8 to 12 keV for high flux applications. For low flux applications, by appropriately increasing the energy to 12.9 keV, the beam flux and flux density is reduced by one-twelfth at 12 keV (Figure S3). Although the higher harmonics ratio is relatively low when the undulator runs at a low K value, the higher harmonics must be further suppressed by a downstream deflector.