ABSTRACT
We present what we believe to be the first measurement of the spectral properties of a soft x-ray laser seeded by a high-order harmonic beam. Using an interferometric method, the spectral profile of a seeded Ni-like krypton soft x-ray laser (32.8 nm) generated by optical field ionization has been experimentally determined, and the shortest possible pulse duration has been deduced. The source exhibits a Voigt spectral profile with an FWHM of 3.1+/-0.3 mA, leading to a Fourier-transform pulse duration of 4.7 ps. This value is comparable with the upper limit of the soft x-ray pulse duration determined by experimentally investigating the gain dynamics, from which we conclude that the source has reached the Fourier limit. The measured bandwidth is in good agreement with the predictions of a radiative transfer code, including gain line narrowing and saturation rebroadening.
ABSTRACT
We report what is to our knowledge the first demonstration of spatial filtering of a high-order harmonic beam into a soft-x-ray laser plasma amplifier at 32.8 nm. After amplification the seed energy is enhanced by a factor of 50, and the beam profile of the amplified beam exhibits an Airy-like shape due to the spatial filtering by the optical field ionized plasma. Moreover, the transverse coherence of the spatially filtered amplified beam is strongly enhanced, resulting in the generation of a peak coherent power of 0.9 x 10(5) to 1.8 x 10(5) W.
