Influence of initial and boundary discharge conditions on soft X-ray amplification in the fast gas-filled-capillary discharge

Summary form only given. It is just ten years since it was experimentally shown by J.J. Rocca (Colorado State University) that gas-filled-capillary discharges are capable to lase in soft X-ray region, first on Ne-like argon (/spl lambda/=46.9 nm), later on Ne-like sulfur (/spl lambda/=60.8 nm), and Ne-like chlorine (/spl lambda/=52.9 nm). However, transition to shorter wavelengths turned to be very difficult even with new powerful apparatus designed for this purpose. Since that time many laboratories have tried to repeat amplification on argon, if nothing else. Only when the role of pre-pulse had been at least partly understood the first amplifications on argon outside Colorado State University were achieved. Recently we summarized this effort and presented our method of internally generated pre-pulse (by capacitive/resistive coupling of the capillary high-voltage electrode with the pulse forming line). Simultaneously we offered our explanation of lower and upper pre-pulse limit (based on different conductivity profile (along the capillary radius) for the fully and partly ionized pre-plasma). In our present paper, we describe our experiments with externally generated prepulse and with different methods of capillary filling by the gas. An influence on soft X-ray radiation is studied with the help of a soft X-ray PIN diode (time-development of the emitted soft X-ray radiation) as well as of a soft X-ray spectrograph (time resolved soft X-ray spectra). It is expected that more precise conditions for reaching population inversion and amplification in the soft X-ray region will be given.