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0Nanosecond laser ablation in a free expansion and in confined modes of erosion laser plasma: physical aspects and applications
D.S. Polyakov1*, V.P. Veiko, A. Ramos-Velazques
1-ITMO University, Saint-Petersburg, Russia
* polyakovdmitry1988@gmail.com
Nanosecond laser ablation is a complex physical process whose various aspects are used for numerous applications. In the simplest case of ablation in the ambient gas atmosphere (free expansion mode) the process consists of the following main stages: absorption of laser radiation and heating material up to evaporation point, transport of evaporated atoms through Knudsen layer, gas-dynamic expansion of vapor/plasma accompanied with possible additional absorption in the plume, mixing of the vapor with ambient gas accompanied with gas phase chemical reactions, condensation inside the plume (formation of nanoparticles and nanoclusters), deposition of condensed species back to the surface. The transition from the ablation in free expansion mode to the ablation in the confined mode (i.e. when the ablation proceeds in thin gap between the ablated material and transparent substrate) may significantly change the parameters of vapor/plasma plume, dynamics of its expansion and related phenomena. Despite that such ablation mode is widely used for several important applications such as CLI^PA [1,2] and LIBT/LIRT [3,4] the physics of the process is steel poorly understood.
In this talk we would like to present the results the of gas-dynamic simulation of nanosecond laser ablation of metals in confined mode with different gap sizes (from several microns up to several hundreds of microns) and in free expansion mode. Fig. 1 demonstrate the example of calculations of vapor density distribution inside the gap, that illustrate spreading of vapor in the radial directions. The results of the simulations are compared with experimental results on laser induced backward transfer of metals on glass substrate. Based on the results of such comparison the general physical picture and features of nanosecond laser ablation in confined mode will be revealed. It will be demonstrated that nanosecond laser ablation in confined mode can be used as a new method of polychromic marking of glasses. Possibilities and limitations of this method will be discussed.
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Fig. 1. Calculated vapour density distribution inside the gap during nanosecond laser ablation of titanium.
The study was financially supported by the Russian Science Foundation (project №24-79-10230).
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