Micro-fluid dynamics via laser metal surface interactions: Wave-vortex interpretation of emerging multiscale coherent structures

Abstract

Lugomer and colleagues have discovered filamentary-like coherent structures in small (∼3 mm diameter) laserbeam-metal-surface interactions. Experimental photographs of a small part of the laser spot area shows frozen "fossil" filament-like structures. We present reasonable arguments and preliminary computer results that suggest that these are due to vorticity deposited by accelerated flows due to blast and shock waves.

Laser-generated Richtmyer–Meshkov and Rayleigh–Taylor instabilities in a semiconfined configuration: bubble dynamics in the central region of the Gaussian spot

“…RMI is known to appear in many natural phenomena ranging from astrophysical to atomic scales as well as in technological applications. Examples include supernova explosion with the formation of circumstellar structures (Kane et al 1999, Peng et al 2003, laser-material interactions (Fukumoto and Lugomer 2003, Zabusky et al 2005, Lugomer 2007, Lugomer 2016, 2017, 2018, laser inertial confinement fusion (Alon et al 1996, Nishihara et al 1998, Shvarts et al 2001, Matsuoka et al 2003, explosive combustion (Yang et al 1993), and shock-tube phenomena (Palekar et al 2007, Balakumar et al 2008, Probyn and Thornber 2013, Ting et al 2014.…”

Laser and Astrophysical Plasmas and Analogy between Similar Instabilities

“…Characteristics of plasma evolution also depend on the laser pulse duration and the wavelength. Considering the ns-LMIs and the wavelengths ranging from the far infrared CO 2 laser (λ = 10.8 µm, τ = 100 ns), to the infrared Nd-YAG laser (λ = 1.06 µm, τ = 40 ns), to the visible Ruby laser (τ = 30 ns, λ = 600 nm),and to the ultraviolet XeCl laser (λ = 308 nm, τ = 16-20 ns), one finds that in all cases plasma expansion depends on the interaction with the surrounding background gas [11,12]. The expanding plasma becomes a mixture of atoms and ions of both, vaporized target material (In, Co, Fe, Ti, etc.…”

“…Dynamics of plasmas created by ultraintense lasers are intended to mimic plasma dynamics in cosmic explosions and planetary cores creating ultrahigh-pressure shocks [47] In this respect, irradiation of a small sphere by an ultraintense laser creates intense shock waves and ultrahigh pressures reaching ~10 12 atmospheres. Such gigantic shock fronts are similar to the thin shock regions at the boundary between a collapsed supernova and the surrounding material-creating a spheroid of super-hot plasma.…”

“…The experiments-shortly described below-have shown that various plasma flow instabilities can be created by laser-matter interaction, which on the metal targets stay permanently after pulse termination. Multipulse laser irradiation of metal surface modulated by parallel micro-scale scratches has been used in order to induce initial multimodal perturbation [12,[57][58][59] Interference of the initial perturbation modes results in the evolution of various plasma flow instabilities on pure metal targets and targets coated by layers of different metal types. The Co-coated steel plate targets of 1 × 1 × 0.05 cm were exposed (in the open configuration) to the beam of XeCl excimer laser (λ = 308 nm, of E = 250-300 mJ, Es ~5 J/cm 2 , I~2.4 × 10 8 W/cm 2 , τ ≤ 20 ns), of the rectangular cross-section with constant power density distribution (top hat profile), and irradiated by N = 12 pulses at the low repetition frequency of 10 Hz.…”

Thermal dynamics-based mechanism for intense laser-induced material surface vaporization

“…Across this layer the continuum hypothesis fails and steep changes in temperature, pressure and density occurs. It has been reported by Zabusky et al [15] that homogeneous boiling of the skin layer of material starts to occur directly beneath the liquid-vapour interface when the interface temperature reaches around 80% of the critical point. This accompanies a significant drop in the surface tension and huge amount of melt liquid superheat.…”