  Pump-probe experiments combining pulses from a X-ray FEL and an optical
femtosecond laser are very attractive for sub-picosecond time-resolved studies.
Since the synchronization between the two independent light sources to an
accuracy of 100 fs is not yet solved, it is proposed to derive both femtosecond
radiation pulses from the same electron bunch but from two insertion devices.
This eliminates the need for synchronization and developing a tunable high
power femtosecond quantum laser. In the proposed scheme a GW-level soft X-ray
pulse is naturally synchronized with a GW-level optical pulse, independent of
any jitter in the arrival time of the electron bunches. The concept is based on
the generation of optical radiation in a master oscillator-power FEL amplifier
(MOPA) configuration. X-ray radiation is generated in an X-ray undulator
inserted between the modulator and radiator sections of the optical MOPA
scheme. An attractive feature of the FEL amplifier scheme is the absence of any
apparent limitations which could prevent operation in the femtosecond regime in
a wide (200-900 nm) wavelength range. A commercially available long
(nanosecond) pulse dye laser can be used as seed laser.
