Generation of coherent XUV radiation in the water window

Summary form only given. He atoms driven coherently by intense laser pulses in the quasi-single-cycle regime are capable of emitting (spatially) coherent x-rays with photon energies in excess of 0.5 keV. Propagation effects have been found to play a dramatic role in shaping the XUV spectrum at high photon energies. Careful optimization of the operating regime will allow the realization of an efficient ultrafast laser pumped coherent XUV sources at high photon energies.