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Radiation Sources
Published in Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull, X-Ray Imaging, 2016
Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull
Another laser-driven x-ray source is an x-ray free-electron laser (FEL), such as the Linac Coherent Light Source (LCLS) built at the Stanford Linear Accelerator Center (SLAC) (Arthur et al. 1995; https://portal.slac.stanford.edu/sites/lcls_public/Documents/lcls_factsheet_2_2014_v6_0.pdf). LCLS produces pulses of x-rays more than a billion times brighter than the most powerful existing synchrotron sources, which are also based on large electron accelerators. The ultrafast x-ray pulses are used much like flashes from a high-speed strobe light, enabling scientists to take stop-motion pictures of atoms and molecules in motion, shedding light on the fundamental processes of chemistry, technology, and life itself. The downside here is again the low energy limit, plus this source also suffers one of the other significant drawbacks of synchrotrons—the large-scale facility investments required limit the number of available sources. Also see Zholents (2012) paper on next generation free electron lasers.
X-Ray Sources
Published in Shalom Eliezer, Kunioki Mima, Applications of Laser–Plasma Interactions, 2008
With an increase in ILλLμm2 above around 1015 W/cm2 μm2 (IL is the laser intensity in units of W/cm2), the collective processes in laser–plasma interaction such as resonance absorption or parametric instabilities start dominating over the absorption mechanism so that plasma electrons have a second component consisting of energetic electrons, that is, hot electrons. The created plasma becomes less collisional and, because of the long penetration depth of hot electrons, plasma is heated nonlocally. Bulk electron temperatures tend to be lower than that for the lower intensity, and x-ray emission mainly arises from inner-shell ionization and subsequent radiative de-excitation. As a result, the observed x-ray lines consist of the primary Ka line from singly ionized ions and the energy-shifted components from partially ionized ions (Nishimura et al., 2003). These multi-keV x-rays are of primary interest in the new fields of ultrafast x-ray diffractometry and biomedical radiography such as x-ray imaging for high-energy density physics. Depending on their energy and the target material (Z), the electrons will typically penetrate several microns into the solid, generating bremsstrahlung and Kα line radiation as they slow down via collisions with cold atoms. The characteristic Kα or Lα radiations have received most attention because of their potential as a monoenergetic, pulse x-ray source.
Sub-20-fs multiterawatt lasers and x-ray applications
Published in S Svanberg, C-G Wahlström, X-ray Lasers 1996, 2020
C. P. J. Barty, T. Guo, C. Blanc, F. Raksi, C. G. Rose-Petruck, J. A. Squier, C. Walker, K. R. Wilson, V. V. Yakovlev, K. Yamakawa
Many applications are presently being pursued or considered for the ultrafast, ultrahigh peak power systems at UCSD. These include the generation of ultrafast x-rays and their use for studies of ultrafast molecular dynamics via time-resolved diffraction or time-resolved x-ray absorption spectroscopy[14], the generation of small source size, short duration hard x-ray radiation for use in high resolution and reduced-dose medical radiography[15], the generation of single femtosecond high order harmonic radiation[16], studies of ultrahigh intensity laser/matter interactions[17], the design of TeV/m laser particle accelerators and the development of keV x-ray lasers.
Attoclock revisited on electron tunnelling time
Published in Journal of Modern Optics, 2019
C. Hofmann, A. S. Landsman, U. Keller
Angular streaking was initially applied to attosecond pulse measurements (58, 59) before we applied it to the attoclock concept (13, 14). To characterize the temporal structure of ultrafast free electron pulses (60, 61) the ultrafast X-ray pulse promotes electrons of a target gas into the continuum by single photon ionization, and these photoelectrons are subsequently streaked by a close to circularly polarized pulse of longer wavelength. However moving away from a pump-probe scheme with circular polarization to a single pulse with elliptical polarization was the key idea to obtain a self-referencing ‘time-zero’ calibration for the attoclock (14). These ideas then for example also have been applied to measure the time-dependent polarization of an ultrashort pulse with sub-cycle resolution (62).