Source challenges resulting from the first applications of a UV storage ring FEL on Super-ACO

On the Super-ACO free electron laser were developed the first applications of a storage ring based FEL and of a UV FEL. The feasibility of use was demonstrated in 1993 with a time resolved polarised fluorescence experiment in biology. After these experiments, the stability of the laser source was significantly improved, with the installation of a longitudinal feedback. A particular advantage of a storage ring FEL source is to provide as well naturally synchronized synchrotron radiation. A first pump-probe time-resolved experiment coupling such two tunable, synchronized light sources was then performed in surface physics.