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Accelerator and Laser Diagnostics (ALD) Group

Investigators

laser
Electro-Optic Laser Diagnostics

Background

The Accelerator and Laser Diagnostics Group at Dundee is a long-term collaboration between Dundee and Abertay Universities and the STFC Daresbury Laboratory near Warrington, Cheshire. This group has been involved with free-electron laser (FEL) research since its pioneering UK activities at Glasgow University's Kelvin Laboratory starting in 1982, and has research collaborations with the FELIX facility in The Netherlands, Stanford University and SLAC in California, the DESY FLASH facility in Hamburg, and the Alpha-X Project at Strathclyde University in the UK (among others).


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Electro-Optic Laser Diagnostics

Many aspects of free-electron laser physics and technology have been investigated over this extended period. In recent years, much of the group’s activity has centred on the ultrafast diagnostics of the bunched extreme-relativistic electron beams used in FELs, advanced light sources and electron linear colliders such as the planned International Linear Collider (ILC). The principle is to "encode" the longitudinal (i.e. temporal) 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 laser beam traversing the crystal, and several non-linear correlation techniques are used to extract the temporal signature from the modulated laser beam with good signal-to-noise.


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Principle of E-O Bunch Diagnostics

By this means temporal resolutions approaching 60 femtoseconds rms have been achieved with the 500 MeV bunches at the DESY FLASH facility, a precursor for X-FEL. Recent work has included incorporation of fibre lasers into the diagnostic systems, producing greater stability and offering the potential to generate very accurate relative timing signals between the electron beam bunches and external lasers, such as those used in pump-probe experiments. Part of our activities involve collaboration with ERLP, the energy recovery linac prototype under construction at Daresbury Laboratory as the test-bed for the planned 4th Generation Light Source (4GLS). Diagnostics developed by the Dundee group are used on ERLP, at DESY FLASH, and are planned for EndStation A at SLAC.


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