We report the first demonstration of a high average power tabletop soft x-ray laser. An average laser output power of $\approx 1\mathrm{mW}$ $(>2\mathrm{}\times {10}^{14}\mathrm{photons}/\mathrm{s})$ was generated at 46.9 nm in Ne-like Ar using a very compact tabletop discharge. The spatially coherent average power emitted by this 26.5 eV laser is comparable to that generated at this photon energy in a similar bandwidth $(\Delta \lambda /\lambda {=10\mathrm{}}^{-4\mathrm{}})$ by a third-generation synchrotron beam line. Lasing was obtained at a repetition rate of 7 Hz with an average output energy of $135\mu \mathrm{J}/\mathrm{pulse}$ by exciting a plasma column in a ceramic capillary with a fast current pulse. This very compact high-repetition-rate laser source makes intense short-wavelength coherent radiation accessible to a wide variety of new applications.

• Received 31 August 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.5804