Dynamics of the plumes produced by ultrafast laser ablation of metals

Abstract

We have analyzed ultrafast laser ablation of a metallic target ͑Nickel͒ in high vacuum addressing both expansion dynamics of the various plume components ͑ionic and nanoparticle͒ and basic properties of the ultrafast laser ablation process. While the ion temporal profile and ion angular distribution were analyzed by means of Langmuir ion probe technique, the angular distribution of the nanoparticulate component was characterized by measuring the thickness map of deposition on a transparent substrate. The amount of ablated material per pulse was found by applying scanning white light interferometry to craters produced on a stationary target. We have also compared the angular distribution of both the ionic and nanoparticle components with the Anisimov model. While the agreement for the ion angular distribution is very good at any laser fluence ͑from ablation threshold up to Ϸ1 J/ cm 2 ͒, some discrepancies of nanoparticle plume angular distribution at fluencies above Ϸ0.4 J / cm 2 are interpreted in terms of the influence of the pressure exerted by the nascent atomic plasma plume on the initial hydrodynamic evolution of the nanoparticle component. Finally, analyses of the fluence threshold and maximum ablation depth were also carried out, and compared to predictions of theoretical models. Our results indicate that the absorbed energy is spread over a length comparable with the electron diffusion depth L c ͑Ϸ30 nm͒ of Ni on the timescale of electron-phonon equilibration and that a logarithmic dependence is well-suited for the description of the variation in the ablation depth on laser fluence in the investigated range.

Femtosecond ultraviolet laser ablation of silver and comparison with nanosecond ablation

“…A similar low-Z impurity peak was observed in fs ablation of Ni. 8 However, with the target stationary only the Ag ion signal is observed. The ion probe signals reported below were obtained after laser ablative cleaning of the target.…”

“…Another significant feature is that most of the experiments on medium, or heavy elements, have been carried with laser wavelengths in the near infrared around 800 nm, 2,6,7 or in the visible at 527 nm, or 620 nm, 3,[8][9][10]13 whereas ns ablation is typically studied for UV lasers at 355 nm or 248 nm. However, one should note that the strong-field excitation induced by fs-lasers makes it possible to ablate materials using longer wavelengths where the materials are transparent to the laser light.…”

“…[15][16][17] There are some reports of ion energy distribution measurements using Langmuir probes 7 or ion energy analyzers, 2,4,7,11 but these measurements have been made in a direction close to the normal of the target surface, and do not give information about the shape of the ablation plume. Donnelly et al 8,9 have used ion probes to measure the plume shape and the ion energy distribution in fs ablation of nickel.…”

“…[1][2][3][4][5][6][7][8][9] It is now well established that fs laser ablation of solids is significantly different from nanosecond (ns) ablation. In fs ablation the time available for heat conduction is of the order of the electron-lattice relaxation time, typically 1-10 ps.…”

Heating and compression of a laser produced plasma in a pulsed magnetic field

“…The laser energy was increased, so as to maintain the laser fluence of 2 J cm À2 . The deposition distributions were obtained by using a flatbed transmission scanner to map the optical transmission of films made, using 8000 shots for the field off and 500 shots with the field on, as described by Donnelly et al 18 The boundary of the deposition in the nofield case (Fig. 5) corresponds to a projection of the coil aperture from the ablation spot.…”