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

Abstract

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 ultraviolet (EUV) laser. Two EUV capillary discharge lasers operating at a wavelength of 46.9 nm were focused onto targets of gold, aluminum, and copper using two different experimental setups to maximize the laser fluence range. The experimental ablation craters were measured using an atomic force microscope, and the depths were compared to the ionizing wave model. The model depends on the dominant ion charge of the ablated plasma, which was measured experimentally using the low fluence setup with a time-of-flight 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 confirmed the trends predicted by the model, showing potential to expand its use to other materials and fluence ranges.