The effects of the prepulse on capillary discharge extreme ultraviolet laser

In the past few years collisionally pumped extreme ultraviolet (XUV) lasers utilizing a capillary discharge were demonstrated. An intense current pulse is applied to a gas-filled capillary, inducing magnetic collapse (Z pinch) and formation of a highly ionized plasma column. Usually, a small current pulse (prepulse) is applied to the gas in order to preionize it prior to the onset of the main current pulse. In this paper we investigate the effects of the prepulse on a capillary discharge Ne-like Ar XUV laser (46.9 nm). The importance of the prepulse in achieving suitable initial conditions of the gas column and preventing instabilities during the collapse is demonstrated. Furthermore, measurements of the amplified spontaneous emission (ASE) properties (intensity and duration) in different prepulse currents revealed unexpected sensitivity. Increasing the prepulse current by a factor of 2 caused the ASE intensity to decrease by an order of magnitude and to nearly disappear. This effect is accompanied by a slight increase in the lasing duration. We attribute this effect to axial flow in the gas during the prepulse