Since the first demonstrations of the ruby laser in 1960, the LASER (Light Amplification by Stimulated Emission of Radiation) found its use in a variety of applications. The reason is that lasers typically produce energy in a highly concentrated way being transferred without direct contact.

The laser is used to drill holes in parts of gasturbines. Here this is done using multiple laser pulses; laser percussion drilling. (see the illustration)

The ultimate goal of this project is to get a full understanding of the laser drilling process and to provide a simulation model in which all physical phenomena that play a role in the drilling process are included.

We summarize the phenomena playing a role.

At relative low intensities: the surface material starts to heat up.

At moderate intensities the surface reaches, at a certain time, the melting temperature and starts to melt.

At even higher intensities the melt reaches the vaporisation temperature and starts to vaporise.

When the vapour reaches a certain pressure the melted material is pushed out.

The melt flows along the relative cold sides, and may on its way even resolidify partially.

The vapour has also an effect on the effectivity of the beam; indeed, it may eventually absorb the radiated energy to such an extent that the material gets shielded by it.

All phenomena mentioned above may interact and happen more than once during one pulse.

We now focus on the melting problem.
The melting problem is modelled through the energy equation in enthalpy form

where is the Heaviside function and L_f is the latent heat of fusion. From this model follows the depth of the meltpool when vaporisation starts. This is used as input for the splashing model. The recoil pressure, an other input for the splashing model, follows from the vaporisation model as sketched below.

Here, the lines between and , and , and between and are the shockwave, the contact discontinuity and the liquid-vapour interface, respectively.

We show some numerical results of the melting model. The picture below shows the temperature distribution in the metal when it's irradiated by a laser beam.

The Scientific Computing Group cooperates in this project with ELDIM B.V. and Rolls Royce plc.