Photothermal Processes for Microstructuring

During the laser microstructuring a roll of solidified melt forms at the edge of the ablated structure, which is called recast (Fig. 8.3). The formation of the recast is due to the material melted and ejected out of the structure by action of the laser pulse. The recast formation can be minimised by reducing the volume of the melted material generated by the pulse [407,488]. The recast is commonly removed by mechanical processes, such as grinding and polishing. 

The precipitation of vaporised material on the surface of the structured glass causes the deposition of debris around the structure formed. The debris formation can be significantly reduced when the laser microstructuring is performed in a suitable environment [261]. Normally, the debris layer does not 

The geometrical microstructuring using CO2 and Nd YAG lasers is a thermal process, in particular if holes are drilled into borosilicate and quartz glass using CO2 lasers [55], 

The elementary volume ablation process, also called EVA process, is a special structuring process using a pulsed CO2 laser. For this process the pulses of the CO2 laser are modified and stabilised using a modulator. Only the material that has to be removed is melted by a pulse and is also completely removed from the materials surface [487-489]. This process minimises the amount of material to be melted and solidified and thereby reducing thermal stresses and the tendency for crack formation. The optical constants of the material are very important for this process. 

Silicate glass was textured using a CO2 laser [330]. The texturing is used to fabricate computer discs of high specific information density made from glass substrates. Laser pulses create a nanotexture on a surface of a glass disc. The process is based on rapid thermal cycles to manipulate the transformation temperature and finally the microstructure of the glass in the zone affected by the heat. 

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