Models For Laser Ablation Mass Removal And Impulse Generation In Vacuum

The complexity of the phenomena simultaneously occurring, from the very first instants of high-power laser pulse interaction with the target up to the phase explosion, along with the strong changes in chemical-physical properties of matter, makes modeling laser ablation a hard task, especially near the thermodynamic critical regime. In this work, we report a computational model of an aluminum target irradiated in vacuum by a gaussian-shaped pulse of 20 ns duration, with a peak intensity of the order of GW/cm2. This continuum model covers laser energy deposition and temperature evolution in the irradiated target, along with the mass removal mechanism involved, and the vaporized material expansion. Aluminum was considered to be a case study due to the vast literature on the temperature dependence of its thermodynamic, optical, and transport properties that were used to estimate time-dependent values of surface-vapor quantities (vapor pressure, vapor density, vapor and surface temperature) and vapor gas-dynamical quantities (density, velocity, pressure) as it expands into vacuum. Very favorable agreement is reported with experimental data regarding: mass removal and crater depth due to vaporization, generated recoil momentum, and vapor flow velocity expansion.

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Enhanced mass removal due to phase explosion during high irradiance nanosecond laser ablation of silicon

10.2172/764401 ◽

2000 ◽

Author(s):

Jong Hyun Yoo

Keyword(s):

Laser Ablation ◽

High Irradiance ◽

Nanosecond Laser ◽

Phase Explosion ◽

Mass Removal ◽

Nanosecond Laser Ablation

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Listening with Curiosity – Tracking the Acoustic Response of Portable Laser Ablation

CHIMIA International Journal for Chemistry ◽

10.2533/chimia.2021.300 ◽

2021 ◽

Vol 75 (4) ◽

pp. 300-304

Author(s):

Stefan Kradolfer ◽

Kurt Heutschi ◽

Joachim Koch ◽

Detlef Günther

Keyword(s):

Laser Ablation ◽

Inductively Coupled Plasma ◽

Method Development ◽

Acoustic Signals ◽

Minimal Invasive ◽

Acoustic Response ◽

Mass Removal ◽

Inductively Coupled ◽

Laser Focus ◽

Plasma Mass Spectrometry

Nowadays, one of the methods of choice for minimal invasive sampling of solid matter is laser ablation (LA). Routine LA sampling is performed commonly in the laboratory and the amount of ablated mass can directly be monitored and analysed. By contrast laser-based sampling in the field, using a portable laser ablation system (pLA), still remains challenging concerning low-absorbing or NIR-transparent samples. The current hardware is limited in regards to photon energy and density resulting in unsteady ablation. But as the actual amount of collected mass is the major crux of on-site sampling, with this performance it is often unknown and estimates can only be made based on the experience from prior method development and the experience of the user. In the following work an easy-to-use method to monitor the amount of ablated material collected during laser-based sampling by measuring the acoustic response is presented. The pLA-system was coupled to inductively coupled plasma mass spectrometry (ICPMS) via a diffusion driven gas exchange device (GED) which allowed to monitor mass removal and acoustic response quasi-simultaneously. For the current instrumentation only actual mass removal leads to the formation of shockwaves (SW) and, thus, acoustic signals. These events can be used as indicator for executed LA events and counted on an individual basis. The intensity of acoustic signals has been shown to correlate with the LA mass, i.e., the amount of ablated material. This allows to perform re-adjustment of the laser focus during sampling for optimal ablation based on the intensity of the acoustic signal. Likewise, acoustic intensity together with counting allows the operator to make estimates about total mass sampled. Therefore, unsuccessful laser aerosol collection in the field shall become a thing of the past.

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