X-Ray Based Subpicosecond Electron Bunch Characterization Using 90 degrees Thomson Scattering.

X rays produced by 90\ifmmode^\circ\else\textdegree\fi{} Thomson scattering of a femtosecond, near infrared, terawatt laser pulse of a 50 MeV electron beam are shown to be an effective diagnostic to measure transverse and longitudinal density distributions of an electron beam ( $e$ beam) with subpicosecond time resolution. The laser beam was focused onto the $e$-beam waist, generating 30 keV x rays in the forward direction. The transverse and longitudinal $e$-beam structures have been obtained by measuring the intensity of the x-ray beam, while scanning the laser beam across the $e$ beam in space and time. The $e$-beam divergence has been obtained through measurement of spatial and spectral characteristics of the scattered x-ray beam.