Level 1

Section 5.6: General materials issues considered in laser machining process

Generally, the following influences of the properties of the processed materials in laser machining process:

Absorptance: Quartz glass is transparent in the wavelength region from 165 to 4000 nm. Therefore it can only be processed with a good quality using the TEA CO2 laser if the laser pulse duration is in the order of ns or longer.

Reflectance: Metals like tantalum can't processed with the TEA CO2 laser in the investigated parameter field because of the high reflectance. Melting respectively evaporation temperature: The ablation depth of materials with high melting and evaporation temperatures like tantalum and A12O3 ceramics is relatively low.

Thermal conductivity: A high thermal conductivity of the processed material causes the formation of molten edges and will make the resolution of the projection process worse.

Thermal expansion coefficient: Large thermal expansion coefficients cause the formation of cracks in brittle materials with low thermal conductivity because of high thermal gradients and high mechanical stress.

Quality of the Surface: Smooth unirradiated surfaces posses mostly a lower absorptance than already ablated surfaces, so that for the initialization of the ablation process a higher laser fluence is necessary. Impurities or water films at the sample surface can cause higher ablation thresholds too.