Characterization of a bright, tunable, ultrafast Compton scattering X-ray source

Abstract

The Compton scattering of a terawatt-class, femtosecond laser pulse by a high-brightness, relativistic electron beam has been demonstrated as a viable approach toward compact, tunable sources of bright, femtosecond, hard X-ray flashes. The main focus of this article is a detailed description of such a novel X-ray source, namely the PLEIADES~Picosecond Laser-Electron Inter-Action for the Dynamical Evaluation of Structures! facility at Lawrence Livermore National Laboratory. PLEIADES has produced first light at 70 keV, thus enabling critical applications, such as advanced backlighting for the National Ignition Facility and in situ time-resolved studies of high-Z materials. To date, the electron beam has been focused down to s x ϭ s y ϭ 27 mm rms, at 57 MeV, with 266 pC of charge, a relative energy spread of 0.2%, a normalized horizontal emittance of 3.5 mm{mrad, a normalized vertical emittance of 11 mm{mrad, and a duration of 3 ps rms. The compressed laser pulse energy at focus is 480 mJ, the pulse duration 54 fs Intensity Full Width at Half-Maximum~IFWHM!, and the 10e 2 radius 36 mm. Initial X rays produced by head-on collisions between the laser and electron beams at a repetition rate of 10 Hz were captured with a cooled CCD using a CsI scintillator; the peak photon energy was approximately 78 keV, and the observed angular distribution was found to agree very well with three-dimensional codes. The current X-ray dose is 3 ϫ 10 6 photons per pulse, and the inferred peak brightness exceeds 10 15 photons0~mm 2 ϫ mrad 2 ϫ s ϫ 0.1% bandwidth!. Spectral measurements using calibrated foils of variable thickness are consistent with theory. Measurements of the X-ray dose as a function of the delay between the laser and electron beams show a 24-ps full width at half maximum~FWHM! window, as predicted by theory, in contrast with a measured timing jitter of 1.2 ps, which contributes to the stability of the source. In addition, K-edge radiographs of a Ta foil obtained at different electron beam energies clearly demonstrate the g 2 -tunability of the source and show very good agreement with the theoretical divergence-angle dependence of the X-ray spectrum. Finally, electron bunch shortening experiments using velocity compression have also been performed and durations as short as 300 fs rms have been observed using coherent transition radiation; the corresponding inferred peak X-ray flux approaches 10 19 photons0s.

Extremely high-intensity laser interactions with fundamental quantum systems

“…Another advantage is that the electrons can be precisely synchronized with the driving laser field. In order to further improve the all-optical setup, design parameters for a proof-of-concept experiment have been analyzed in Hartemann et al, 2007. For the calculation of the Compton scattering parameters, a 3D Compton scattering code has been used, which was extensively tested for Compton scattering experiments performed at LLNL Hartemann et al, 2004Hartemann et al, , 2005) (see Sun and Wu, 2011 for an alternative numerical simulation scheme). It is shown that x-ray fluxes exceeding 10 21 s −1 and a peak brightness larger than 10 19 photons/(s mrad 2 mm 2 0.1% bandwidth) can be achieved at photon energies of about 0.5 MeV.…”

“…solutions with an exponentially-diverging electron acceleration, even in the absence of an external field (see the books Hartemann, 2001 andRohrlich, 2007 for reviews on these issues).…”

Advanced Compton scattering light source R&D at LLNL

“…T-REX experiments have been already performed on an enhanced version of the 100 MeV LLNL electron linac used for previous Compton scattering sources [2]. The electron bunch is accelerated to ~120 MeV and focused with a series of quadrupole magnets.…”

More power to X‐rays: New developments in X‐ray spectroscopy

“…Several important diffraction measurements were performed with this source, though the results will not be reviewed here. A similar X-ray-generation mechanism is used to produce Compton scattering through electron beam-intense laser interactions (PLADEIS), as described by Hartemann et al [62,63]. Currently, two other FEL operating in the X-ray region are being built, one in Europe (FLASH) and one in Japan.…”