Antonin Billaud1, Patrick A. Taschner2, Maik Steinbach2, Arndt Hohnholz2, Jürgen Koch2, Oliver Suttman2, Gwenn Pallier1, Pu Jian1, Olivier Pinel1, Guillaume Labroille1
1 Cailabs, Rennes, FRANCE 2 Laser Zentrum Hannover e.V., Hannover, GERMANY
In the past few years the need to process thinner glass sheets with increasing speed has developed. Thinner sheets imply a more flexible and elastic material, allowing the development of more sophisticated touch panel displays or fingerprint displays. Microprocessing of glass with Ultra-Short Pulse (USP) lasers leads to a high level of quality since the amount of energy is delivered within a short time window, allowing matter to be ablated without melting or cracking.
USP lasers associated with appropriate beam shaping modules lead to a significant process quality improvement. Particularly, the use of Bessel beam allows drilling holes down to the nanometer scale. Bessel beams present a high energy central spot over a very small area with a long depth of field. Nevertheless, shaping USP lasers beams is challenging due to inherent characteristics of the beam including high peak power, as well as temporal and chromatic dispersion.
A new way to generate Bessel beams for material processing has been developed using a reflective off-axis axicon. Compared to Spatial Light Modulator or refractive optics which already generate Bessel beams, a reflective axicon improves the beam quality: a higher aspect ratio, a longer depth of field, and a profile closer to theory are obtained. Such a reflective axicon and its associated optical set-ups have been designed. The test program includes thin glass processing. The characteristics of the beam and of the processed thin glass are described, as well as the capacity to process at high speed.
Processing tests are carried out using different Bessel beams including small beams (2 to 4 microns diameter over 450 to 2000µm working depth) associated to a x10 microscope objective, and larger beams (20 to 40µm diameter over 45 to 200mm working depth) associated to a 100mm Effective Focal Length F-theta lens. Compared to a Gaussian focus this offers working depths which are around 100 times larger. A 10ps 1064nm laser carrying 170µJ per pulse at a Pulse Repetition Frequency of 100kHz is used.