100 Hz repetition rate, high average power, plasma-based soft x-ray lasers*

Numerous applications demand high average power / high repetition rate compact sources of coherent soft x-ray radiation. We report the demonstration table-top soft x-ray lasers at wavelengths ranging from 10.9nm to 18.9nm from plasmas created at 100Hz repetition rate. Results includes a record average power of 0.15mW at $\lambda =$18.9nm from a laser-produced Mo plasma and 0.1mW average power at $\lambda =$13.9nm from a Ag plasma. These soft x-ray lasers are driven by collisional electron impact excitation in elongated line focus plasmas a few mm in length heated by a compact, directly diode-pumped, chirped pulse amplification Yb:YAG laser that produces 1J pulses of ps duration at 100Hz repetition rate. Pulses from this laser irradiate the surface of polished metal targets producing transient population inversions on the 4d$^{1}$S$_{0}\to $4p$^{1}$P$_{1}$ transition of Ni-like ions. Tailoring of the temporal profile of the driver laser pulse is observed to significantly increase soft x-ray laser output power as well as allow the generation of shorter wavelength lasers with reduced pump energy.