ENERGY MODULATION OF THE ELECTRONS BY THE LASER FIELD IN THEWIGGLER MAGNET: ANALYSIS AND EXPERIMENT

Energy modulation of the electron beam after the interactionwith the laser field in the wiggler magnet can be calculated usinginterference of the laser field and the field of spontaneous emission inthe far field region of wiggler radiation. Quite often this approachgives a deeper insight on the process than traditional calculations wherethe effect of the laser field on the electron energy is integrated alongthe electron trajectory in the wiggler. We demonstrate it by showing theagreement between the analytical model and the experiment involvingwiggler scan measurements with large detuning from the FEL resonanceproducing more than one order of magnitude variations in the amplitude ofthe energy modulation. The high sensitivity was achieved using the THzradiation from a sub-mm dip in the electron density that energy modulatedelectrons leave behind while propagating along the storage ring lattice.All measurements were performed at the BESSY-II electron storagering