Prepulse effect for recombining plasma produced by ultrashort high-intensity lasers

We compare the space-resolved characteristics of carbon plasmas produced us ing a single ultrashort high-intensity laser pulse (> 10(19) W/cm(2)) of le ss than 800 fs duration and those using a combination of a 100 ps duration prepulse and an ultrashort laser pulse. Profiles of electron density and el ectron temperature as functions of position from the original target surfac e are derived from the measured one-dimensional space-resolved soft X-ray s pectra. The electron density was estimated from the Inglis-Teller limit and from a comparison of the experimental and the calculated profiles of Lyman series lines. The electron density gradually increases up to the critical density of the incident laser light near the target surface, and the densit y gradient is much steeper when the plasma is produced using the single ult rashort pulse. The electron temperature was estimated from the intensity ra tio of the H-like Ly-beta line to the He-like He-beta line and that of the H-like Ly-alpha line to its satellite lines. The plasmas produced using the prepulse additionally are relatively uniform with moderate electron densit y and temperature, and a larger portion of the K-shell lines from carbon io ns is produced in the recombining phase, rather than in the heating phase. With a suitable choice of prepulses, the spatial and temporal profiles of t he plasma density and temperature can be controlled, which can facilitate a pplications of the laser-produced plasmas to various kinds of research, suc h as producing a gain medium for X-ray lasers.