P. Rebernik Ribic, D. Gauthier, G. D. Ninno, E. Allaria, P. Cinquegrana, M. Danailov, A. Demidovich, E. Ferrari, L. Giannessi, B. Mahieu, G. Penco

Elettra-Sincrotrone Trieste, Italy

We demonstrate spectro-temporal shaping of extreme-ultraviolet (XUV) pulses from the FERMI seeded free-electron laser (FEL). By precisely manipulating the linear frequency chirp of the seed and tuning the FEL operating parameters we generate Fourier limited pulses or short trains of pulses locked in phase. Furthermore, using a twin-seed configuration we are able to produce two time-delayed pulses whose relative phase can be controlled with attosecond precision. Some of these pulses were directly characterized using spectral phase interferometry for direct electric-field reconstruction (SPIDER).

We also present a scheme that will allow manipulating the transverse radiation profile of the FERMI FEL. Placing a phase mask with a transverse staircase-like phase pattern in front of the seed laser will make it possible to generate XUV beams carrying orbital angular momentum (OAM). The setup will soon be tested at FERMI and can easily be implemented at any seeded FEL facility without extensive modifications of the machine layout.