Threshold behaviour of ion formation for noble metals (Au, Ag, Cu, Pt) irradiated by 4 ns 532 nm laser

There have been no reports about the formation of metallic ions below the threshold of ablation, i.e. ∼1 J/cm2. In this work, generation of ions under the irradiation of 532 nm laser on the Au, Ag, Cu, and Pt targets under 4.6 × 103 Pa helium gas has been studied. The fluence was changed from the threshold of ion formation to the start of ablation. We have found that metallic ions started to be observed with the fluence that was about two orders of magnitude lower than that of the ablation threshold, ∼10 mJ/cm2, for all the surface-roughened metal targets investigated. The surface plasmon resonance excitation was provoked for the ion formation. Desorption of neutral species was suggested to be minor for the mass transfer from the surface to the gas phase below the threshold of the ablation.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (196 K)Download as PowerPoint slideHighlights► Positive and negative ions were measured for Au, Ag, Cu and Pt targets using 532 nm ns laser. ► Threshold values for the formation of ions were about two orders of magnitude lower than those for ablation. ► Surface plasmon excitation plays a major role for the formation of positive ions rather than the heat effect. ► Electron attachment to the desorbed atoms was suggested for the formation of negative ions.