Ions and Atoms in Superfluid 4 Helium: Motion Studies and Optical Transitions

Abstract

In this paper systematic studies of the ion production mechanism are reported. The use of laser ablation inside the liquid is compared to the laser sputtering technique which produces the ions in the gas phase. For the first time impurity ions produced directly in the liquid could be separated from other sputtering products in the laser focus and identified unambigously by their characteristic emission light during the recombination process with electrons emitted from a field emission tip. This technique is important for future, pressure dependent measurements of the ionic mobility in liquid helium when ion production in the gas phase is impossible. Furthermore, optical transitions of various elements implanted into liquid helium are reported which became observable due to an improved set-up used in this experiment.