Controlling of surface ablation threshold of fused silica by double-pulsed femtosecond laser

Femtosecond laser (fs) ablation is an effective method to processing waveguide, microfluidic channel and other functional devices in fused silica glass. The accuracy of ablation is critical for high-performance devices. In this paper, a double-pulse femtosecond laser was used to control the surface ablation threshold of fused silica. It was found that, when the delay time of the double pulses ranged from 0 to 100 ps, with the increasing of delay time, the ablation threshold first rapidly increased to the maximum value, then fell to a stable value. And the overall threshold was higher than the threshold at 0 ps, which means the processing accuracy could be significantly improved. By simulating the relationship between the maximum electron density of conduction band and the time delay, it can conclude that the modification of threshold was caused by the difference of maximum electron density. In addition, to find the more optimized processing parameters, we also studied the weights of the two sub-pulses at 10 ps. These results provide an important reference for ultra-precision machining.