Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Final Activity Report Summary - ECOLAMP (Enhancement and control of laser-assisted material processing)

The use of laser technology in industry, to create micron scale features in a range of materials, is typically assumed to exploit laser-induced thermal processes that result in melting or vaporisation of the solid and theoretical models normally include only thermal processes.

The principal objective of the work-programme in this project was to develop a fundamental understanding of the laser ablation process through modelling/simulations and to use this understanding to underpin the applied research programmes in laser material processing which are in progress at the host institution.

In particular, the project was also aimed at understanding the mechanism involved in:
(i) hybrid laser processing steps in which an ambient gas or vapour was used as an assist medium; and
(ii) how the rapid mechanical changes that accompany laser absorption could affect the final structures formed.

Primarily because of the sheer complexity of the models required to do it properly, this latter effect has been ignored in most previous attempts at simulation of these interactions. In order to tackle this challenging problem, two experienced researchers were recruited, with specific expertise in:
(a) thermodynamic simulations of vapour - liquid systems; and
(b) thermo-mechanical effects arising from short pulse laser material interactions.
A third, more-experienced, researcher - whose expertise was complementary to that of the experienced researchers - was recruited later for two separate three-month periods and the combined team worked well together for these three-month periods of overlap.

The expertise profile of the fellows was chosen to deliver specific objectives:

(a) To develop a thermodynamic description of laser material interactions in different ambient environments. The goal was to understand how the presence of additional effects could influence laser ablation - with particular application to laser machining of silicon in the presence of assist gases. We also had experimental data on the effects of electric fields applied in conjunction with the laser beam. In the first instance, the process of silicon ablation had to be modelled and then more advanced simulations were developed which included gas-assist. Finite element Monte Carlo models of vapour-assisted silicon machining have been developed and these models have successfully reproduced the main features of the extensive experimental data that have been accumulated by the NCLA over the past four years.

From the results of these models, we can now justify the phenomenon of very efficient debris removal in relation to different parameters like assist gases, power of laser beam, geometry of environment, etc. Experiments conducted in the NCLA show that some assisted gases improve efficiency of ablation and others reduce it. A model involving creation of shock waves and expansion was developed to explain the results.

(b) To develop realistic models that take full account of the thermo-mechanical effects that occur in laser ablation. The essential task was the elaboration of the theory of short pulse.

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