Extreme ultraviolet laser ablation and time of flight mass spectrometry of gold, aluminum, and copper targets

An ablation crater depth estimation model, founded on the concept of an ionizing bleaching wave, has been developed for metal targets irradiated by an extreme ultra-violet (EUV) laser. Two EUV capillary discharge lasers operating with a wavelength of 46.9 nm were focused onto targets of gold, aluminium and copper using two different experimental set-ups to maximise the laser fluence range. The experimental ablation craters were measured using an atomic force microscope and the depths are compared to the ionizing wave model. The model is dependant on the dominant ion charge of the ablated plasma, which has been measured experimentally using the low fluence set-up with a Time of Flight (TOF) mass spectrometer. The measured ablation depths and ion charges at low fluences are in agreement with the model. The ablation crater depths in the higher fluence range have confirmed the trends predicted by the model showing potential to expand its use to other materials and fluence ranges.