Investigating the dynamics of fast capillary discharges leads to soft X-ray laser realization at 46.9 nm

The dynamic evolution of plasma columns, generated by a fast capillary discharge setup, was measured by an "off-axis" imaging apparatus. Appropriate initial conditions were found where stable compression of the plasma column could be obtained. The appearance of a sequence of shock and refraction waves during the plasma column compression is clearly seen. Relative line emission from Ne-like and F-like Ar ions at 25-50,Å spectral range was used for electron temperature and density measurements, during the column compression. Appropriate conditions for soft x-ray laser operation were found at the time the first shock wave reaches the axis. Indeed, strong soft x-ray amplification at 46.9nm (3s-3p, J=0-1) was measured at this stage. The small signal gain of the measured amplified line is ∼0.9 cm^-1 and the beam divergence is less than 5mRad.