  This paper describes a scheme for pump-probe experiments that can be
performed at LCLS and at the European XFEL and determines what additional
hardware development will be required to bring these experiments to fruition.
It is proposed to derive both pump and probe pulses from the same electron
bunch, but from different parts of the tunable-gap baseline undulator. This
eliminates the need for synchronization and cancels jitter problems. The method
has the further advantage to make a wide frequency range accessible at high
peak-power and high repetition-rate. An important feature of the proposed
scheme is that the hardware requirement is minimal. Our technique is based in
essence on the "fresh" bunch technique. For its implementation it is sufficient
to substitute a single undulator module with short magnetic delay line, i.e. a
weak magnetic chicane, which delays the electron bunch with respect to the SASE
pulse of half of the bunch length in the linear stage of amplification. This
installation does not perturb the baseline mode of operation. We present a
feasibility study and we make exemplifications with the parameters of the SASE2
line of the European XFEL.
