DEMONSTRATION OF SOFT-X-RAY LASING TO GROUND-STATE IN LI-III

Soft x-ray lasing with a gain length GL approximate to 5.5 was demonst rated in hydrogenlike Li III at 13.5 nm (2-1 transition) in a 5 mm lon g LiF microcapillary using a 50 mJ, 250 fs UV laser beam at a 2 Hz rep etition rate. The initial plasma was created in the 0.3 mm diameter mi crocapillary by a low power Nd/YAG laser. The strongly nonlinear incre ase of the 13.5 nm line intensity with increasing microcapillary lengt h was compared with a linear increase of the Li III 11.4 nm (3-1 trans ition) line intensity.