Angular distributions of flux and energy of the ions emitted during pulsed laser ablation of copper

An experimental study on the pulsed laser ablation of copper by using Nd-YAG laser radiation of 1064 nm wavelength at a fluence of 13 J/cm2 is reported. A time-resolving plane Langmuir probe, placed at various angles with respect to the target surface normal, is used to record temporal variation of ion currents during the plasma expansion in vacuum. The measured angular distributions of integrated ion yields are strongly peaked in forward direction. The experimentally determined plume expansion coefficient Zinf/Xinf = 2.1±0.2 is in good agreement with the previous studies. Time-of-flight measurements indicated that the energy of various ion components is highest along target surface normal and decreases with increase of the angle, however the effect of angle is more pronounced on the faster ions. The energy spread of the ions decreases approximately from ±670 eV to ±19 eV as the probe angle increases from 0° to 60°. The measured angular dependence of ion yield and most probable ion energy nicely follows the trends predicted by Anisimov's plume expansion model