Speaker
Description
We will present the first results of an experiment performed at the FERMI FEL to generate few-femtosecond extreme-ultraviolet (XUV) pulses using a recently developed slippage-compensation scheme in externally seeded free-electron lasers. Building on this approach, we will also show the results of a theoretical study aimed at extending the scheme to generate multiple few-femtosecond XUV pulses, in particular pulse pairs, with tunable topological properties and adjustable temporal delay. Simulations show that the topological charge l of each pulse can be independently set to l=−1,0,1, while the delay can be tuned from a few to several tens of femtoseconds. Compared with superradiance, the proposed scheme offers greater flexibility, as it does not require driving the FEL into saturation and suppresses SASE emission from the unseeded portion of the electron beam, which can be substantial at longer wavelengths. Combined with pulse-to-pulse polarization switching, the proposed approach could enable XUV studies of circular and helical dichroism in chiral systems and magnetic materials, as well as high-resolution imaging, in the few-femtosecond regime.
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