Occurrence of erosion processes in the near-surface region of metals exposed to intense nanosecond laser pulses

Possibility of applying a hydrodynamic model to describe the laser erosion of metals irradiated by high-intensity nanosecond pulses

“…To experimentally study the optical characteristics of laserproduced plasma (using the techniques of transverse laser probing [10,11] and laser-induced plasma spectroscopy [12]) in this work we employed a research complex, which comprised the means for monitoring the dynamics of the spectral, spatial, and phase structures of laser-produced plasma plumes (LPPs) of metals with a high temporal resolution.…”

“…The investigations of Refs [11,12] showed that the peak of erosion plume glow for t = 20 ns (I ~ 10 9 W cm -2 ) is located at less than 1 mm from the target surface, while for pulses of similar intensity with t = 100 ns [10] at 1 - 2 mm (which is attributable to the higher energy density). This permits characterising the spatial scales of erosion plumes early in their nonstationary formation in atmospheric conditions.…”

“…When the rise time of a laser pulse is sufficiently short (10 -8 - 10 -9 s), even for I ~ 10 8 - 10 9 W cm -2 the abrupt interphase boundary between the condensed metal phase and its vapour becomes nonabrupt and turns into a macroscopic transition layer, whose thickness is determined by the depth of light pulse penetration (5 - 10 mm) [19]. In this layer there occurs dissipation of the laser pulse energy, resulting in its fast (as fast as permitted by the inertia of the matter) transformation to an overheated, rapidly expanding vapour (according to the estimates of Refs [10,11], its initial expansion velocity amounts to 10 - 20 km s -1 ), which subsequently forms the erosion plume. This vigorous gas-dynamic process imparts a substantial recoil pressure momentum to the laser target, generating an acoustic shock wave propagating into the target material [20].…”

“…The detonation of a metal macrolayer, which possesses considerable excess energy, has the effect that there appears an intensely glowing plasma-vapour plume at the surface plasma region with a short delay relative to the onset of laser irradiation (5 - 10 ns for a pulse of duration t = 20 ns [11] and 30 - 40 ns for t = 100 ns [10]). This plume rapidly expands into the ambient medium and interacts with the irradiating laser pulse [12].…”

“…This permits characterising the spatial scales of erosion plumes early in their nonstationary formation in atmospheric conditions. The data obtained in the probing of erosion plumes at 1 and 2 mm from the metal target surfaces permitted estimating the velocity of their propagation through these spaces at 4 - 15 km s -1 for t = 20 ns [11] and at 7 - 20 km s -1` for t = 100 ns [10] (I = 10 9 W cm -2 ), depending on the type of metal. The fact that shortening the leading edge of a pulse does not entail an increase in the initial velocity of the plasma plume suggests that these velocities are the limiting ones for the irradiation regime under discussion and that the initial plume dynamics is determined only by the macrolayer detonation velocity (i.e.…”