Capillary z-pinch for recombination pumping of EUV lasers

Abstract

Our aim is to achieve lasing at 13.38 nm wavelength, using excited hydrogen-like nitrogen ions (N6+)*. The primary pumping process is a three-body collisional recombination, taking place in a non-stationary under-cooled plasma created during the pinch expansion stage. To design optimum parameters of the device we have performed computer modeling for various capillary radii and current pulse shapes, presuming the capillary wall ablation is negligible. We came to the conclusion that for capillary with radius 1.6 mm a measurable gain is predicted only if the current slope is greater than 1.1012 As-1 and current peak value is greater than 50 kA. We report here new results of simulations for capillary filled by boron and compare them with previous nitrogen results. In both cases the same capillary radius and current pulse shape are taken into account. Evaluated pressure optimized gains are 1 cm-1 and 0.1 cm-1 for boron and nitrogen, respectively. Efficient amplification of spontaneous emission at boron Balmer alpha (26.23 nm) may be achieved with lower current peaks and lower current slopes than for nitrogen (13.38 nm). Greater pumping efficiency of hydrogen like ions with lower atomic number was expected. It corresponds to the smaller ionization potential and lower electron plasma temperature needed to get required abundances of fully ionized atoms. The role of wall ablation is also judged and compared for alumina and boron nitride capillaries with both capillary fillings. The ablated material has cooling effect; the electron temperature on the axis is lower than in the case without wall ablation.