Fig. 2: Experimental setup.
a Scheme of the TIMER instrument in the OP beam configuration. The two beams generated by the FEL source are split vertically by a planar mirror PM1 to generate the probe (see panel c). Of the remaining two half beams, the variably polarized one (LH/LV) is steered by the second planar mirror PM2 whereas the LV branch propagates unaffected. Both half beams constitute the pump and are crossed and focussed at the sample at an angle 2θ by two toroidal mirrors FM1 and FM2. Of the two half beams reflected by PM1, the variably polarized one is geometrically blocked while the LV is steered to the delay line and then focussed at the sample at an angle θpr. The signal beam is drawn exemplary to propagate in forward diffraction at an angle θsig. b Scheme of the OP beam generation in the FERMI undulator chain (see text for discussion).
