Glass-to-glass welding using ultrashort pulse laser is attracting attention. However, the low processing speed and the requirement of the small air gap between glass substrates have impeded its use in industry. In our study, we achieved rapid welding of glass substrates by coaxially focusing a single femtosecond laser pulse and a continuous-wave (CW) laser with a wavelength that transmits through glass. The selective absorption of the CW laser into the excited electrons increased the processing speed by a factor of 500 compared to the conventional method, while the allowable gap increased by a factor of 4.
Recently, ultrashort pulse laser processing has been attracting attention as a method for microprocessing SiC. However, there is a severe problem with this technique: cracks formed around the processed shape hinder precision processing. In this study, to reveal the mechanism of crack formation during the ultrashort pulse laser processing of SiC, we investigated the high-speed phenomena happening during processing. The phenomena were captured using an imaging system consisting of the pump-probe imaging method and a high-speed camera. The ultrashort pulse laser and the high-speed camera are operated at 1 kHz in synchronization, which enables us to capture the high-speed phenomena during processing that change as the process progresses. As a result, we have succeeded in capturing the damage formation process. The results show that the damage is generated and grows only near the tip of the processed hole and does not change once it is generated. As known from previous studies, stress waves propagate around the tip of the processed hole during machining, suggesting a strong correlation between stress waves and damage generation. The larger the pulse energy, the more damage is generated, due to the large stress waves generated because of the large removal volume. When the pulse width is long, the material is thermally affected, and thermal damage is thought to occur at the entrance of the processed hole.
The extreme intensity of femtosecond laser pulses can enable microfabrication in glass. However, conventional femtosecond laser based glass processing has two severe limitations, viz., a low processing speed and the generation of damage during processing. To create a hole with a diameter of 10 m and a depth of over 100 μm using the conventional method, hundreds of pulses must be focused on a single spot because the volume removed by a single femtosecond laser pulse is too small. Furthermore, whenever a laser pulse is focused on the target surface, a strong stress wave is generated, thereby hindering precision. We have resolved these issues by coaxially focusing a single femtosecond laser pulse and a fiber laser pulse having a wavelength that is transparent to glass. A hole with a diameter of 10 μm and a depth of 133 μm was created in 40 μs, which indicates that the processing speed was over 5000 times faster than that of a conventional femtosecond laser. Moreover, the damage generated was considerably eliminated in comparison with the conventional method, and precision processing was achieved. The results of this study will help expand the industrial applications of femtosecond laser processing.
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