Hi JP,
I'm afraid the best Blue Kenue can offer is the ability to export iso-lines to ArcGIS shape files.
That being said, you could generate a TIFF file but you'll have to adjust the data values.
1. "File->New->Regular Grid" to create a "raster" at your desired resolution and covers the area of interest.
2. "Tools->Map Object" to map that data from your t3 mesh to the regular grid.
3. Select the regular grid and using "File->Save As" export it as a GeoTIFF.
Hope this helps... Martin