Numerical Calculations of Pulsed Laser Heating of Non-isotropic Materials

Gamborg Andersen, G., Petrunin, V.V., Baurichter, A.
University of Southern Denmark, Physics Department, Odense, Denmark

We used FEMLAB (Finite Element Modelling LABoratory) for modelling heat propagation in 4 dimensions (time and the 3 spatial dimensions) after pulsed laser heating of non-isotropic materials during surface science experiments.

As an example, the spatial and temporal evolution of a laser induced temperature jump in highly oriented pyrolytically grown graphite (HOPG) was calculated on a ns time scale. This material exhibits a thermal conductivity which is higher by three orders of magnitude in the planes of the chemically bonded network (basal planes) as in the perpendicular lattice directions. As input parameters, the spatial and temporal laser intensity profiles are needed. They were measured by means of a CCD-camera and a fast photo diode, respectively. The average energy in the laser pulse was measured by a power meter.

The image from the camera, together with the measured temporal distribution and the energy readings, were transferred via MATLAB to FEMLAB, where they were analyzed in terms of time resolved energy dissipation in 3 dimensions.

The 3-D analysis allows us to analyse nonaxially symmetric laser spots, and account for possible hotspots in the laser beam. The temperature distribution was evaluated by a heat conduction model.

A special feature of our FEMLAB routine is that it can be interfaced with the physical setup in the laboratory. As an output it returns readings of specific relevant temperatures of the graphite surface. First results agree well with temperature estimates based on experimental observations.