Short-pulse UV laser ablation of solid and liquid metals: indium

Abstract

Laser-ablation experiments on solid (T = 300 K) and liquid (T = 600 K) indium are reported. The ablation was performed under high vacuum conditions with UV laser pulses at 248 nm and pulse durations of 15 ns and 0.5 ps. The ablated neutral indium atoms were resonantly ionized with a second laser pulse 28 mm above the sample surface and detected in a time-of-flight mass spectrometer. The ablation threshold fluence for solid indium decreases by a factor of 40 from 100 mJ/cm 2 to 2.5 mJ/cm 2 when a 0.5 ps pulse is used instead of a 15 ns laser pulse. Measurements on liquid indium show a different behavior. With 15 ns laser pulses the threshold fluence is lowered by a factor of ∼ 3 from 100 mJ/cm 2 for solid indium to 30 mJ/cm 2 for liquid indium. In contrast, measurements with 0.5 ps laser pulses do not show any change in the ablation threshold and are independent of the phase of the metal at 2.5 mJ/cm 2. This behavior could be explained by thermal diffusion and heat conduction during the laser pulse and demonstrates in an independent way the energy lost into the material when long laser pulses are applied. Time-of-flight measurements to investigate the underlying ablation mechanism show thermal behavior of the ablated indium atoms for both ps and ns ablation and can be fitted to Maxwell-Boltzmann distributions.

Impacts of Ambient and Ablation Plasmas on Short- and Ultrashort-Pulse Laser Processing of Surfaces

“…Up to date, very few systematic studies are known on laser ablation of liquid metals. Some examples include comparison of ablation dynamics for metals in solid and liquid states [71][72][73], thermal modeling of molten gallium ablation to understand the causes of high energies of the expanding ablation products [74], experiments on imaging the laser ablation dynamics and the irradiated surface response [75,76], generation of hot electrons and X-rays under fs laser ablation of molten metals [77], and GaN film deposition by pulsed laser ablation of liquid gallium in a nitrogen atmosphere [78]. In [70], during multishot ns laser irradiation (IR and UV) of liquid metals in the presence of reactive ambient gases, a tower-like structure (called below "microtower") with the diameter somewhat exceeding the irradiation spot size was growing on the irradiated surface at an average rate of 3-20 μm per pulse.…”

Modeling of UV pulsed-laser ablation of metallic targets

“…The average values have been computed on a time interval comparable with the duration of the vaporization process the emission process are important. Recently, time-of-flight investigations of solid and liquid metallic target laser ablation by using UV laser pulses in the ns and fs regime have been reported [32,33]. These experimental studies have been carried out at extremely low ablation rates (i.e.…”

Investigation of ion charge composition and energy distribution of laser ablation plasma from liquid metal

“…Really, in this case absorbing media is restored by itself in a short time under action of forces of surface tension. Moreover, for a liquid state absorbing media the ablation threshold is expected to be much lower as compared with solid state one, and the efficiency much higher [3].…”