Two-color transient pumping in Ni-like silver at 13.9 and 16.1 nm

We report on progress in the optimization and understanding of the collisional pumping of x-ray lasers in the transient regime using an ultrashort subpicosecond heating pulse. An irradiation scheme using a frequency-doubled 600-ps laser pulse to preform the plasma is tested. The effect of traveling-wave irradiation on the time-integrated and time-resolved lasing signal at the 4d¹S₀→4p¹P₁ Ni-like Ag line is studied in detail. Under specific irradiation conditions, strong lasing is also obtained on another spectral line at 16.05 nm that is identified as the 4f¹P₁→4d¹P₁ transition in Ni-like Ag.