<title>Microablation of pure metals: laser plasma and crater investigations</title>

Abstract

Crater shapes and plasma plume expansion in the interaction of femtosecond (70 fs), picosecond (20 ps) and nanosecond (6 ns) laser pulses (wavelengths-800 nm; 400 nm and 266 nm for femtosecond Ti-Al203 laser ; 1064 nm, 532 nm and 266 nm for nanosecond and picosecond Nd-YAG lasers; mode-nearly TEM00; waist diameter-of the order of 1 0 jim) with various pure metals in air and noble gases at atmospheric pressure were studied. The craters formed at the surfaces were measured by an optical microscope profilometer with O.O1im depth and O.5im lateral resolutions. The measurements of laser plasma expansion were carried out with ICCD camera with 3 jim spatial and 1 ns temporal resolutions. These measurements were made in 0-100 ns time delay range and at different wavelengths in 200-850 nm optical spectral range. Laser ablation efficiencies, crater profiles, plasma plume shapes at different time delays, rates of plasma expansion in both longitudinal and transversal directions to the laser beam were obtained. Experimental results were analyzed from the point of view of different theoretical models of laser beam interaction with plasma and metals. The laser pulse duration range used in our study was of particular interest, as it includes the characteristic time of electron-phonon relaxation in solids, that is, of the order of one picosecond. Thus, we could study the different regimes of laser ablation without (for fs pulses) and with (for ns pulses) laser beam/plasma plume interaction. It was found that for nanosecond pulses the laser beam absorption, as well as its scattering and reflection in plasma, were the limiting factors for efficient laser ablation and precise material processing with sharply focused laser beams.

Analytical performances of laser-induced micro-plasma of Al samples with single and double ultrashort pulses in air and with Ar-jet: A comparative study

“…This is in correlation with the results of our previous studies [17]. Crater volumes, depths and diameter were the same for metal samples irradiated by pulses with 50 fs -1 ps durations with identical experimental parameters [10][11]. In addition, the analysis of plasma images with 50 fs or 1 ps pulse durations has demonstrated that plasma reheating was identical in both the cases [16][17].…”

“…The efficiency of Al sample ablation with 50 fs -1 ps pulses does not depend on the laser pulse duration [10][11]13]. For 50 fs pulses, the maximum pulse energy did not exceed 40 µJ so that the undesirable nonlinear effects inherent to fs laser propagation in air (10 µm waist spot) may be avoided.…”

“…With micro-LIBS applying ns laser pulse durations, the surface analysis was provided with a spatial resolution of the order of some micrometers [4]. Microablation with ultrashort laser pulses (fs and ps) has demonstrated the improved analytical performances (depth and lateral resolution, ablation efficiency) along with a higher accuracy of matter sampling and reduced thermal damage of the target surface [8][9][10][11][12][13][14].…”

Laser-Induced Breakdown Spectroscopy for Mars surface analysis: capabilities at stand-off distances and detection of chlorine and sulfur elements

“…The two major mechanisms significant for sampling of solids are melting followed by vaporisation and explosion of macroparticulates caused by mechanical effects, which can depend on grain size and density of each sample. Our previous results [33] showed that metals with lower melting temperature give greater crater volumes, which suggested that an important role in the crater formation should be attributed to processes dealing with plasma -target interaction and liquid matter ejection. Thus, we can suppose that liquid matter ejection could play an important role in the ablation process of metals explaining the presence of a protrusion along the crater boundary.…”