Traveling-wave scheme for the transient pumping of X-ray laser with a sub-ps TW pulse

Summary form only given. High efficiency of the transient collisional excitation (TCE) pumping of X-ray lasers has been demonstrated recently. TCE relies an the rapid increase of the electron temperature in a preformed plasma irradiated with a short picosecond pulse. This plasma is created by a sub-nanosecond pulse and contains a predominant proportion of the lasant ions. The gain duration is limited to a few ps by several effects such as plasma cooling or ionization while the transit time of the amplified emission along a 1 cm long plasma column is 33 ps. This results in the temporal detuning of the optimal plasma conditions as the X-ray laser pulse propagates. A way to overcome this detuning is to use a travelling wave irradiation of the plasma at the velocity of the X-ray laser pulse. We perform this task by laterally pumping the gain medium by focusing an inhomogeneous pulse (IP) along the plasma column.