Femtosecond ultraviolet laser ablation of silver and comparison with nanosecond ablation

Abstract

The ablation plume dynamics arising from ablation of silver with a 500 fs, 248 nm laser at ∼2 J cm−2 has been studied using angle-resolved Langmuir ion probe and thin film deposition techniques. For the same laser fluence, the time-of-flight ion signals from femtosecond and nanosecond laser ablation are similar; both show a singly peaked time-of-flight distribution. The angular distribution of ion emission and the deposition are well described by the adiabatic and isentropic model of plume expansion, though distributions for femtosecond ablation are significantly narrower. In this laser fluence regime, the energy efficiency of mass ablation is higher for femtosecond pulses than for nanosecond pulses, but the ion production efficiency is lower.

Ion distribution and ablation depth measurements of a fs-ps laser-irradiated solid tin target

“…Early studies, employing ion energy analyzers, identify these pulses as light element contaminations. 12,15 Energy-dispersive X-ray spectroscopy measurements reveal that areas on our tin target unexposed to laser light contain a substantial amount of oxygen and other low-mass elements, such as carbon and nitrogen. These elements are only barely visible, if at all, for an irradiated target area.…”

“…In the experiments, we average over five shots (shots No. [10][11][12][13][14] per target position as well as over 30 separate target positions, i.e., 150 shots in total. Shots later than shot No.…”

“…In almost all studies, the wavelength of the laser is in the infrared, where commercial laser systems are readily available. The focus is often either on the ablation depth or ion distributions (energy, yield, or angular), with a few exceptions such as the work of Toftmann et al, 12 which addresses both. A detailed study of laser ablation of the relevant element tin, including both depth and ion emission distribution, has not yet been performed in the fs-ps domain.…”

“…There they could be used for generating a fine-dispersed liquid-metal target 10 before the arrival of a high-energy main-pulse responsible for the EUV emission, enhancing laser-plasma coupling. 11 The utilization of a fs-ps laser system could strongly reduce fast ionic and neutral debris from EUV sources compared with nanosecondpulses, 12 enabling a better machine lifetime. 13 Since the 1990s, many experiments have been performed and models developed 2,3 for laser-matter interaction at this particular time scale.…”

“…13 Since the 1990s, many experiments have been performed and models developed 2,3 for laser-matter interaction at this particular time scale. Target materials used are metals such as gold, silver, copper, and aluminum, 5,12,[14][15][16][17][18][19][20][21] and non-metals such as silicon [22][23][24][25] and metal oxides, [26][27][28] among others. 29,30 Most of these studies are conducted in a femtosecond pulse length range from 50 fs up to approximately 1 ps and a pulse fluence up to 10 J/cm 2 .…”