ARTICLE:

• HEAT TRANSFER AND PHASE CHANGE DURING HIGH POWER PULSED LASER ABLATION OF METAL  download article

Xianfan Xu
Mechanical Engineering Department Purdue University, 1288 Mechanical Engineering Building West Lafayette, IN 47907-1288, USA

ABSTRACT

High-power, nanosecond pulsed lasers are finding many attractive applications. Examples include: thin film deposition, micromachining, and nanomaterials synthesis. In these processes, the intense radiation flux from the laser is transformed to the target material, inducing rapid heating, melting, and evaporation. Owing to the fast heating-rate, the melted material can be superheated to a metastable state. When the temperature of the melt approaches the thermodynamic critical point, it undergoes a phase explosion that turns the melt into a mixture of liquid and vapor. This article describes, in detail, heat transfer and phase-change phenomena during pulsed laser ablation. Experimental diagnostic techniques and numerical calculation procedures are presented. Nanosecond time-resolved measurements of the velocity and radiative properties of the laser-generated plasma and the recoil pressure of ablation reveal the phase change mechanisms and the interface kinetic relation during laser ablation. Experiments are performed in a laser fluence range between 2.5 J/cm² and 10 J/cm² (between 100 MW/cm² and 400 MW/cm²). Superheating of the liquid phase, explosive phase change, and nonequilibrium kinetic relation at the liquid/vapor interface are found to exist. Conclusions obtained are based on the study of pulsed excimer laser ablation of a nickel target, however, they are generally applicable to nanosecond pulsed laser ablation of a metal.

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79-115 pages

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