Effects of nanosecond-duration laser prepulses on solid targets

A critical issue in high-intensity laser-solid interactions is the effect of the laser prepulse on the target, but the experimental details of these lower-intensity interactions are often difficult to measure due to the subsequent high-intensity pulse. We have performed target experiments using a 0.5-ns duration, 800-nm wavelength laser pulse, specifically designed to mimic the typical amplified spontaneous emission (ASE) prepulse from a high-power Ti:Sapphire laser. Using this ''artificial'' ASE prepulse, we find that the threshold for relevant changes to typical solid targets occurs at a fluence of ∼0.1 J/cm2, or ∼108 W/cm2, well below the plasma formation threshold. Notably, the results are not consistent with simple surface vaporization, and suggest that the ASE prepulse causes multiatom clusters to be ejected from the target surface. In a full high-intensity experiment, this ablated material would then strongly interact with the subsequent primary laser pulse