Saturated Amplification of a Collisionally Pumped Optical-Field-Ionization Soft X-Ray Laser at 41.8 nm

We report the first saturated amplification of an optical-field-ionization soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 330-mJ, 35-fs, 10-Hz Ti:sapphire laser system in a few-mm cell filled with xenon. A gain of $67\mathrm{cm}{}^{-1\mathrm{}}$ on the ${4d}^{9}5p-{4d}^{9}5d$ transition at 41.8 nm in Pd-like xenon and a gain-length product of 15 have been inferred at saturation. This source delivers about $5\times {10}^9$ photons per pulse. The influence of the pumping energy and the laser polarization on the lasing output are also presented.