Established mechanical methods for machining of fragile materials such as saw cutting and scribing often cannot satisfy the industrial needs or requires extensive post processing to meet the needs in terms of quality and throughput. Nowadays, lasers are increasingly used for machining of different types of materials. Laser cutting processes such as melting, vaporization and fusion cutting are used for cutting of ductile materials like metals and polymers. These methods are not appropriate for cutting of transparent or semi-transparent materials to meet required high quality and cutting speed standards.
As for instance known from D. Helie and R. Vallee, “Micromashining of Thin Glass Plates with a Femtosecond Laser”, Proc. of SPIE Vol. 7386, 738639, Photonics North 2009, for such cutting of transparent materials a controlled fracture technique is a well suitable method for machining of those materials.
When curvilinear and close shaped internal features are needed to be cut a laser direct ablation process can be used. However, the ablation rate, i.e. the processing speed of the direct ablation method, is scaled with the laser average power and normally limited to several mm/s. Besides of slow processing speed the formation of cracks, contamination by ablation debris, collateral damages along cut (heat affected zone) are typical disadvantages of the laser direct ablation processes.
Application of femtosecond laser filamentation for machining of glass substrate is an interesting alternative to the direct ablation process. An idea of fast cutting of a display glass where the sample is pre-processed using femtosecond laser pulses prior to glass cleaving was proposed by Ahmed et al. (F. Ahmed, M. S. Lee, H. Sekita, “Display Glass Cutting by Femtosecond Laser induced single shot periodic void array”, Appl. Phys. A (2008) 93, 189-192). The maximum processing speed achieved in this study was 15 mm/s. The speed has been limited by the minimum distance between voids, because it was not possible to cleave the sample when void period was larger than 10 μm.
The stress build-up and micro-defects induced by filamentation are known for being used for cutting of thin borosilicate glass substrate and for production of simple 3D parts from different types of glass. However, controlling of the generated cutting edge cannot be realised by this technique, hence the application of above proposed methods for cutting of curvilinear and internal features is not feasible.
Therefore, it is an object of the present invention to provide an improved processing method for (e.g. transparent or semi-transparent) materials, wherein a more precise processing of the material, particularly in terms of quality of a cutting edge, along a desired processing path with higher processing speed (e.g. >15 mm/s) is enabled.
A further object of the invention is to provide a laser cutting method which enables to cut curvilinear or other shape contours in a transparent or semi-transparent material with high precision and speed.