Travelling wave chirped pulse amplified transient pumping for collisional excitation lasers

A approximately ps travelling wave chirped pulse amplified pulse at 6×10¹⁴ W cm^-2 superimposed on approximately 300 ps background pulses is shown to be an efficient method to pump transient collisional excitation X-ray lasers in both Ni-like and Ne-like ions. Measurements of X-ray laser output as a function of plasma length are fitted with results of an amplified spontaneous emission model of the laser output taking account of travelling wave pumping effects. A small signal gain coefficient approximately 42 cm^-2 and a effective gain length product of approximately 18 are measured for the Ni-like Sn laser at 120 angstroms. Simulations from a hydrodynamic and atomic physics code (EHYBRID) coupled to a ray trace code show that a spatially averaged small signal gain approximately 65 cm^-2 can be obtained in Ne-like Ge provided the optimum pumping pulse arrangement is used.