Micro drilling of PMMA with double-pulse femtosecond laser

Micro holes drilling in polymers have a variety of applications in industry and research. Especially, the fabrication of micro hole with high aspect ratio is a key technology for advanced applications. In this work, we report an improvement in drilling on poly-methyl methacrylate (PMMA) by using double-pulse femtosecond laser. Compared to single pulse, the achievable depth by double pulses can be increased by 50% when the pulse delay is 100 fs and gradually decreases with delay increasing. The depth evolution with the increasing of pulse number is investigated. When the micro hole depth reaches a certain value, the processing speed of double pulse is less restricted than single pulse. Furthermore, the relationship between the depth improvement and electrons decay together with absorption increase is studied.