Laser-induced ionization of ions from liquid alloy ion sources of high brightness

In this work, we have generated ion beam targets of metal and metalloid ions using a high-brightness liquid metal ion source (LMIS) originally applied in focused ion beam systems. Using an eutectic Au-Si alloy as a low melting point source feed material, ions of different ion species were detected: Si^{2+}, Si^+, Au^{2+}, Au^+, Au^{2+}, Au^{3+} and Au^{32+}. The source current between emitter needle and extractor electrode is in the range of 10 - 60 μA and can be adjusted up to about 150 μA. The ion source is characterized by high ion current stability and a suitable emission lifetime of several days, which is limited by the amount of material and can be further increased.
To study the strong-field laser ionization, we used a E x B filter and selected Si^{2+} and Au+ ions as ionic targets, because of their high beam intensity. We investigated ultrafast laser-induced ionization, which leads to higher charge states after multiple ionization of both ion species. Laser intensities of up to 10^{16} W/cm^2 allow observation of up to 10-fold ionization of Au^+ ions and 3-fold ionization of Si^{2+} ions.
The aim of further work is to extend the available ion beam targets to other elements of the periodic table to study ultrafast laser-induced fragmentation and ionization dynamics of atoms and molecules in strong laser fields. Another goal is the further increase of the density of ion laser targets for more reliable statistics and shorter measurement times. Further steps are technical improvements of ion source and ion optics as well as the investigation of heavy metal dimers such as Au^{2+}.