Traveling wave excitation and amplification of neon-like germanium 3p–3s transitions

We report on experiments using traveling wave excitation of neon-like germanium to produce amplification of 3p–3s soft X-ray transitions. The laser pulse consisted of three 100 ps Gaussian laser pulses separated by 400 ps. Targets were 3 cm long germanium slabs. Traveling wave excitation was employed by tilting the wave front of the driving laser by 45 degrees to match the propagation speed of the X-ray laser photons along the length of the target. We compare cases with the traveling wave, with no traveling wave, and against the traveling wave. Significant enhancement of the X-ray laser intensities is observed using the traveling wave technique due to the short gain duration of these plasmas. Gain was inferred from line intensity measurements at two lengths. Our results are compared to a numerical model.