Investigation of the Characteristics of Laser Post-Ionization for Laser-Induced Plasma and Ion-Beam-Sputtered Neutrals

Abstract

The characteristic behaviors of the post-ionized signals of neutral atoms generated by either ion beam sputtering or laser ablation were investigated by adopting a Pb plate as a target sample. The signal intensities and the threshold laser power for ion generation were compared for various the ion generation schemes, such as laser ablation with 532 nm laser only (Case I), 2-color resonant laser ablation by using 532 nm and 283.3 nm lasers (Case II), laser ablation with 532 nm laser followed by resonant post-ionization with 283.3 nm laser (case III), and 2-color resonant laser ablation followed by resonant post-ionization (case IV). Case I required the highest threshold laser power required for ion generation while Case III with a 500 ns delay between the two laser pulses, 532nm and 283.3 nm, required the least laser power for the generation of ion signals. A comparison of the ion signal intensities between case II and case IV revealed a variation in the signal intensity that depended on the time delay between the ablation laser pulse and the ionization laser pulse. Meanwhile, the post-ionization of the neutrals generated by ion beam sputtering (case V) showed a comparable ion signal to that of the post-ionization signal of the laser-induced plasma. The resonant post-ionization of the sputtered neutrals showed a more than 10 times signal enhancement with the use of a 100 times less laser power, 0.6 mW, when compared to the case of non-resonant laser ionization with 60 mW at 355 nm. The behavior of the ion signal of the sputtered neutrals was also investigated by varying the experimental parameters, such as the time delay between the ion beam pulse and the laser pulse, the ion beam pulse and the high voltage pulse for ion extraction, and the high voltage applied to the ion extraction.