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Abstract:
X-ray free-electron lasers have revolutionized x-ray science by achieving unprecedented
intensities exceeding 1018 W/cm2. However, they lack temporal coherence and controllability
of their pulses' temporal and spatial properties, which is essential for many
applications. We investigate the possibility to control and shape x-ray laser pulses with
optical light. An optical laser pulse is used to control the population inversion on the
2p -> 1s transition in a neon x-ray laser pumped by an x-ray free-electron laser. Theoretical
results are presented based on population and photon rate equations. We study
the dependance of the x-ray laser's output on the pump pulse's and the optical laser
pulse's properties. Small-signal gain calculations reveal that for a high degree of control
narrowband pumping radiation is required and the optical laser pulse must have precise
timing with respect to the pump pulse. Self-consistent gain calculations show that it will
be possible to do spatial pulse shaping and to produce high-intensity, sub-femtosecond
pulses that are controlled by and synchronized to the optical laser pulse with femtosecond
precision. Our results indicate that the presented scheme would make it possible
to establish pump-probe techniques with femtosecond x-ray and optical pulse
