Ultrafast and precision drilling of glass by selective absorption of fiber-laser pulse into femtosecond-laser-induced filament

The extremely intense light emitted from femtosecond laser pulses enables micro-drilling of glass. However, there are problems in femtosecond laser drilling, including low drilling speed and the damage during drilling. Because the volume removed by one femtosecond laser pulse is too small, hundreds of pulses must be focused on a single spot to create a hole with a diameter of 10 μm and a depth of over 100 μm. Furthermore, strong stress waves generated during the processing cause damage around the hole. In our research, we achieved ultrafast and precision drilling by coaxially focusing a single femtosecond laser pulse and a fiber laser pulse, with a wavelength that is transparent to the glass. A hole with a diameter of 10 μm and a depth of 133 μm was created in 40 μs, which indicates that the drilling speed was over 5000 times faster than that of conventional femtosecond laser drilling. By investigating the phenomena occurring after laser irradiation, we demonstrated that ultrafast drilling occurred because the fiber laser pulse was selectively absorbed by a high-aspect-ratio filament induced by the femtosecond laser pulse. Moreover, damage generation was inhibited because the material was thermally removed. The results help expand the range of applications for femtosecond laser processing in industry.