Early plume expansion in atmospheric pressure midinfrared laser ablation of water-rich targets

Zhaoyang Chen and Akos Vertes

Phys. Rev. E 77, 036316 – Published 25 March 2008

Abstract

We have developed a one-dimensional fluid dynamics model for the ablation of water-rich targets by nanosecond infrared laser pulses at atmospheric pressure. To describe the laser-target interaction and the plume expansion dynamics, in light of recent experimental results the model incorporates phase explosion due to superheating and the nonlinear light absorption properties of water. In the model, the phase explosion is treated as a prolonged process that lasts for a finite time. Once a thin layer beneath the target surface exceeds the phase explosion temperature, this layer is transformed from target material into a mixture of water vapor and droplets and become part of the plume. This process is sustained for some time until the laser energy cannot maintain it. The simulation results show that as a result of two different phase transition mechanisms, i.e., surface evaporation and phase explosion, a first, slower plume expansion phase is followed by a more vigorous accelerated expansion phase. The calculated time evolution of the shock front at various fluence levels agrees well with the experimental observations of Apitz and Vogel [I. Apitz and A. Vogel, Appl. Phys. A. 81, 329 (2005)]. This model sheds light on the effect of phase explosion in laser ablation dynamics and its results are relevant for material synthesis, surface analysis, and medical (surgery) applications.

Received 16 October 2007

DOI:https://doi.org/10.1103/PhysRevE.77.036316

Authors & Affiliations

Zhaoyang Chen and Akos Vertes^*

Department of Chemistry, The George Washington University, 725 21-st Street, N.W., Washington, DC 20052, USA

^*Corresponding author.

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Issue

Vol. 77, Iss. 3 — March 2008

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Images

Figure 1
Mass density and constant pressure specific heat capacity of liquid water as a function temperature.Reuse & Permissions
Figure 2
(Color online) (a) Time profiles of laser irradiances with the total fluence of $1.4 J ∕ {cm}^{2}$ . The original profile and the attenuated laser irradiance at the target surface are represented by dashed and solid lines, respectively. (b) Calculated surface temperature and (c) interface displacement for laser fluence $1.4 J ∕ {cm}^{2}$ . (d) Comparison of experimental shock front position data (●) with our fluid dynamics calculations in the presence of phase explosion (◻). Extrapolating the linear fit of the final $R (t)$ segment to $R = 0$ provided onset time of phase explosion (solid line).Reuse & Permissions
Figure 3
(Color online) Spatial distribution of water (a) temperature, (b) number density, and (c) velocity in the target and plume domains for a fluence of $1.4 J ∕ {cm}^{2}$ at $100 ns$ (before phase explosion) and $125 ns$ (during phase explosion).Reuse & Permissions
Figure 4
(Color online) Time progression of plume number density distributions for $1.4 J ∕ {cm}^{2}$ Er:YAG laser ablation of water into (a) $1 atm$ nitrogen gas and (b) vacuum at $200 ns$ (1), $400 ns$ (2), $600 ns$ (3), and $800 ns$ (4). The distributions in (a) show a high density region close to the shock front and the pileup of background gas in front of the interface. Solid lines indicate water vapor density, whereas the dashed lines denote background gas density. Horizontal dashed lines indicate the gas density at atmospheric pressure.Reuse & Permissions
Figure 5
(Color online) (a) Temporal laser irradiance profiles for a total fluence of $5.4 J ∕ {cm}^{2}$ . The incident laser irradiance and the attenuated laser irradiance at the surface are represented by solid and dashed lines, respectively. (b) Calculated surface temperature and (c) interface displacement for laser fluence $5.4 J ∕ {cm}^{2}$ . (d) Comparison of experimental shock front position data (●) for $5.4 J ∕ {cm}^{2}$ laser fluence with our fluid dynamics calculations (◻). Extrapolating the linear fit of the final $R (t)$ segment to $R = 0$ provided onset time of phase explosion (solid line).Reuse & Permissions
Figure 6
(Color online) (a) Temporal laser irradiance profiles for a total fluence of $0.12 J ∕ {cm}^{2}$ . The incident laser irradiance is indistinguishable from the irradiance arriving to the interface (optically thin plume). Compared to the two higher fluences in Figs. 2, 5, (b) significantly lower surface temperatures and (c) interface displacements are calculated for $0.12 J ∕ {cm}^{2}$ laser fluence. (d) Comparison of experimental shock front position data (●) for $0.12 J ∕ {cm}^{2}$ laser fluence with our fluid dynamics calculations (◻).Reuse & Permissions

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