PNNL

Abstract

This work investigates extreme ultraviolet (EUV) emission at 13.5 nm from laser-produced tin plasmas generated using a mass-limited laser blow-off (LBO) plume created from a 1 µm Sn foil using 1064 nm, 6 ns Nd:YAG laser pulses. The LBO method produces a low-density, spatially extended pre-plume whose mass distribution can be precisely tuned through the interpulse delay between a low-energy pre-pulse and a higher-energy main heating pulse. Experiments using EUV spectroscopy, Nomarski interferometry, shadowgraphy, and retarding field ion analysis reveal that heating the LBO plume significantly enhances laser–plasma coupling and reduces self-absorption compared to conventional bulk or foil Sn targets. Optimal delays yield up to a 35% improvement in relative in-band conversion efficiency. Electron-density measurements show that LBO-generated plasmas form large, low-density regions favorable for efficient absorption of the heating pulse, as well as reduced density gradients. Ion diagnostics further indicate increased ion flux and reduced ion velocities at optimal delays. HELIOS simulations are shown to be in agreement with experimental results, and indicate that higher temperatures are reached in the case of heated LBO plume.