Laser and Particle Beams



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


F.V.  HARTEMANN  a1 c1 , A.M.  TREMAINE  a1 , S.G.  ANDERSON  a1 , C.P.J.  BARTY  a1 , S.M.  BETTS  a1 , R.  BOOTH  a1 , W.J.  BROWN  a1 , J.K.  CRANE  a1 , R.R.  CROSS  a1 , D.J.  GIBSON  a1 , D.N.  FITTINGHOFF  a1 , J.  KUBA  a1 , G.P.  LE SAGE  a1 , D.R.  SLAUGHTER  a1 , A.J.  WOOTTON  a1 , E.P.  HARTOUNI  a1 , P.T.  SPRINGER  a1 , J.B.  ROSENZWEIG  a2 and A.K.  KERMAN  a3
a1 Lawrence Livermore National Laboratory, Livermore, CA
a2 University of California at Los Angeles, Department of Physics and Astronomy, Los Angeles, CA
a3 Massachusetts Institute of Technology, Physics Department, Cambridge, MA

Article author query
hartemann fv   [Google Scholar] 
tremaine am   [Google Scholar] 
anderson sg   [Google Scholar] 
barty cp   [Google Scholar] 
betts sm   [Google Scholar] 
booth r   [Google Scholar] 
brown wj   [Google Scholar] 
crane jk   [Google Scholar] 
cross rr   [Google Scholar] 
gibson dj   [Google Scholar] 
fittinghoff dn   [Google Scholar] 
kuba j   [Google Scholar] 
le sage gp   [Google Scholar] 
slaughter dr   [Google Scholar] 
wootton aj   [Google Scholar] 
hartouni ep   [Google Scholar] 
springer pt   [Google Scholar] 
rosenzweig jb   [Google Scholar] 
kerman ak   [Google Scholar] 
 

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 [sigma]x = [sigma]y = 27 [mu]m 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 1/e2 radius 36 [mu]m. 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 × 106 photons per pulse, and the inferred peak brightness exceeds 1015 photons/(mm2 × mrad2 × s × 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 [gamma]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 1019 photons/s.

(Received November 1 2003)
(Accepted January 26 2004)


Key Words: Calibrated foils; Compton scattering; Relativistic electron beam; Velocity compression; X-ray source.

Correspondence:
c1 Address correspondence and reprint requests to: F.V. Hartemann, Lawrence Livermore National Laboratory, L-280, P.O. Box 808, Livermore, CA 94551-0808, USA. E-mail: hartemann1@llnl.gov


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