Operation and output pulse characteristics of a discharge-pumped 46.9 nm soft X-ray laser with larger inner diameter capillary and higher discharge currents

We report a significant improvement of the output pulse energy of 46.9 nm laser obtained when we increase the amplitude of main current pulse from 27 to 45 kA. More importantly, we experimentally observed the impact of Ar discharge pressure and main discharge current on laser intensity and beam characteristics of 46.9 nm laser. When we increased the main current amplitude up to 45kA, the laser pulse energy increased to 1.55 mJ with its maximum value for newly employed larger diameter capillary. Here, we have performed symmetric measurements of the exit beam size and divergence of the 46.9 nm laser. The laser spots were captured over a broad range of discharge parameters. The laser beam divergence and spot size increased significantly as we increased Ar initial discharge pressure. At the same time, the spatial intensity distribution of the laser beam changed from a single peak pattern to a ring shape profile. These effects are results of increased refraction of the laser beam, caused by larger density gradients at higher initial Ar pressure inside the plasma column. Furthermore, the main discharge current was increased gradually to moderately increase the laser intensity and to improve the divergence and uniformity of the laser beam. The laser spots of 46.9 nm laser captured at different discharge pressures exhibit good cylindrical symmetry and support the experimental results of laser intensity. This study is conducted to advance the divergence and uniformity of the laser beam of a 46.9 nm discharge-pumped Ne-like Ar soft X-ray amplifier by reducing the plasma density gradients at the time of lasing. We have investigated, by using one-dimensional Magneto-hydrodynamics (MHD) simulations, the impact of main current pulse amplitude and discharge pressure of Ar on pinching time and plasma radius. The lasing and amplification are observed in 4.8 mm inner diameter aluminum channel having a length of 35 cm. This work presents a method to improve laser beam characteristics and laser pulse energy.