Glass processing is a subject of high interest for electronics, watch and consumer electronics industries. The femtosecond laser has unique capacity to produce a high-quality surface or bulk modification in dielectrics transparent materials thanks to nonlinear absorption. Temporal pulse shaping seems to be a smart and flexible solution to further increase the efficiency of this tool. Indeed, since the lifetime of free electrons in the conduction band is about few picoseconds, it is possible to improve ablation efficiency of dieletrics using a double pulse laser irradiation. The principle is to use the first pulse to promote electrons into the conduction band meanwhile the second one induces the ablation of the target material. This study deals with double femtosecond laser pulse radiation of fused silica in order to tune both ablation threshold and removal rate. The time delay between the two pulses is set from 0 to 5 ps owing to a delay line. The results are discussed in terms of optical transmission and ablation efficiency. Our ultrafast laser operates at 1030 nm and has a pulse duration of 480 fs.
Nowadays processing of transparent materials, such as glass, quartz, sapphire and others, is a subject of high interest for worldwide industry since these materials are widely used for mass markets such as consumer electronics, flat display panels manufacturing, optoelectronics or watchmaking industry. The key issue is to combine high throughput, low residual stress and good processing quality in order to avoid chipping and any post-processing step such as grinding or polishing. Complimentary to non-ablative techniques used for zero-kerf glass cutting, surface ablation of such materials is interesting for engraving, grooving as well as full ablation cutting. Indeed this technique enables to process complex parts including via or blind, open or closed, straight or small radius of curvature patterns. We report on surface ablation experiments on transparent materials using a high average power (70W) and high repetition rate (1 MHz) femtosecond laser. These experiments have been done at 1030nm and 515nm on different inorganic transparent materials, such as regular and strengthened glass, borosilicate glass or sapphire, in order to underline their different ablation behavior. Despite the heat accumulation that occurs above 100 kHz we have reached a good compromise between throughput and processing quality. The effects of fluence, pulse-to-pulse overlap and number of passes are discussed in terms of etch rate, ablation efficiency, optimum fluence, maximum achievable depth, micro cracks formation and residual stresses. These experimental results will be also compared with numerical calculations obtained owing to a simple engineering model based on the two-temperature description of the ultrafast ablation.