X-ray lasing on the 4d — 4p transitions of Ni-like molybdenum ions

We outline the results of experiments in the generation of X-ray laser radiation on the 4d — 4p Ni-like ion transitions at a wavelength λ = 189 Å under sequential irradiation of plane targets by two laser pulses focused to a line. These experiments were executed on the Sokol-p picosecond laser facility. The average energy of a 4-ps long ultrashort pump pulse was equal to 6.5 J, the energy of a 0.44-ns long prepulse was equal to 2.7 J, and the time delay between them was equal to 1.5 ns. The effective gain for short target lengths was equal to ~24 cm^-1. In the travelling pump wave regime, which was realised using a ladder mirror, we obtained an 8-fold increase in output X-ray laser energy in comparison with the output energy obtained in the ordinary target irradiation regime.