Traveling wave-pumping of ultra-short-pulse x-ray lasers

Pumping of proposed inner-shell photo-ionized (ISPI) x-ray lasers places stringent requirements on the optical pump source. We investigate these requirements for an example x-ray laser (XRL) in Carbon lasing on the 2p - 1s transition at 45 Å. Competing with this lasing transition is the very fast auger decay rate out of the upper lasing state, such that the x-ray laser would self-terminate on a femto-second time scale. XRL gain may be demonstrated if pump energy is delivered in a time short when compared to the auger rate. The fast self-termination also demands that we sequentially pump the length of the x-ray laser at the group velocity of the x- ray laser. This is the classical traveling wave requirement. It imposes a condition on the pumping source that the phase angle of the pump laser be precisely de-coupled from the pulse front angle. At high light intensities, this must be performed with a vacuum grating delay line. We also include a discussion of issues related to pump energy delivery, i.e. pulse-front curvature, temporal blurring and pulse fidelity. An all- reflective optical system with low aberration is investigated to see if it fulfills the requirements. It is expected that these designs together with new high energy (>1J) ultra-short pulse (<40 fs) pump lasers now under construction, may fulfill our pump energy conditions and produce a tabletop x-ray laser.