ABSTRACT
Over the last several years the use of the prepulse technique has gained wide spread acceptance and opened the door for producing X-ray lasing in low-Z neon-like ions. We present germanium experiments which compare the relative merits of using the prepulse technique to compensate for refraction as compared with the use of curved targets. With the multiple pulse technique, which uses a series of 100 ps pulses 400 ps apart to illuminate germanium targets, we present results which show the 3p - > 3s, J = 0 - > 1 transition at 196 A to completely dominate the other laser lines. Time resolved data shows the usual pair of J = 2—> 1 lines at 232 and 236 a to lase after the J = 0—» 1 line. Using these short pulses together with a traveling wave geometry we are able to produce bright, short X-ray pulses which can be used in imaging experiments. Using the multiple pulse technique we also demonstrate lasing at 79 a in nickel-like neodymium. To understand these plasmas, we present the first high-magnification, two-dimensional, spatially-resolved, near-field images of the laser output for the multiple-pulse driven germanium plasma. LASNEX hydrodynamic results are combined with XRASER kinetics and radiation transport calculations to model these plasmas. Those results are input to a refraction code to predict the spatial and angular output of the laser. We present a comparison of the experimental results with the simulations.
