Measurement of Femtosecond Electron Bunches

Proposed linear colliders like the ILC, advanced light sources, free-electron lasers and plasma wakefield accelerators all rely on bunches of charged particles with ultrashort temporal profiles, in some cases as short as tens of femtoseconds. Accurate measurement of the time profile of such intense bunches presents special experimental difficulties, and requires optical methods based on ultrafast lasers and nonlinear optics.

This talk will describe my group’s activities over the last few years to push these measurements to new limits. The principle behind our measurements is to “encode” the longitudinal structure of the intense electron bunches in these devices by utilising the transverse Coulomb field of the bunch to cause birefringence in a suitable crystal placed close to the beam axis, but not intercepting the beam itself. The birefringence induced by the bunch passage alters the polarisation of a collinear Ti:S or fibre laser beam traversing the crystal, and non-linear correlation techniques are used to extract the temporal signature with good signal-to-noise from the modulated laser beam.

By this means temporal resolutions approaching 60 femtoseconds rms have been achieved with the 500 MeV bunches at the DESY FLASH facility at Hamburg, a precursor for the X-FEL.

The Dundee group has been involved with free-electron laser (FEL) research since its pioneering UK activities at Glasgow University’s Kelvin Laboratory in the 1980s. It has research collaborations with the FOM FELIX facility in The Netherlands, Stanford University and SLAC ESA in California, the DESY FLASH facility in Hamburg, and the Alpha-X Project at Strathclyde University (among others). It also has a long-term collaboration with Abertay University and STFC Daresbury Laboratory, and is currently working on the ERLP, the energy recovery linac prototype under construction at Daresbury as a test-bed for any planned UK 4th Generation Light Source.

Event resources