Effects of capillary discharge current on the time of lasing onset of soft x-ray laser at low pressure

The laser spike of Ne-like argon 46.9 nm pumped by a capillary discharge is measured with an x-ray diode (XRD) at low Ar pressure (25 Pa). Changing the rise-time and amplitude of the main current, we observe the effects of current on the time of the laser spike. The experimental results show that the time of lasing onset, which is the time of the laser spike after the onset of the main current, is larger than 40 ns and almost constant when the rise-time and amplitude of the current are changed. The theoretical results are calculated with the snow-plough model and show that the plasma is pinched several times before the laser spike occurs.