Multiscale Investigation of Femtosecond Laser Pulses Processing Aluminum in Burst Mode

ABSTRACT

Megahertz is the highest femtosecond laser repetition rate that the state-of-the art technology can achieve. In this article, a single femtosecond laser pulse is burst into multiple femtosecond laser pulses to process aluminum. The temporal gap between two consecutive burst pulses is 2 picoseconds, which is much shorter than the temporal gap between two consecutive pulses at the repetition rate of megahertz. By taking the thermophysical scenarios of femtosecond laser induced of electron thermalization, electron heat conduction, electron–phonon-coupled heat transfer and atomic motion into account, a multiscale framework integrating ab initio quantum mechanical calculation, molecular dynamics and two-temperature model are constructed. The effect of femtosecond laser pulse number on the incubation phenomenon is studied. Comparing with the single pulse-processing aluminum film, the femtosecond laser in burst mode leads to smaller thermal stress, which is favorable to reduce the thermal mechanical damage of the material beneath the laser-irradiated surface. Appreciable differences among the simulation results by using electron thermophysical parameters from ab initio quantum mechanical calculation and those from experimental measurement, empirical estimation and calculation are found, indicating the essentials to precisely model the electron thermal response subject to femtosecond laser excitation.

KEYWORDS:

• Femtosecond laser
• electron–phonon-coupled heat transfer
• multiscale modeling
• laser burst mode

Additional information

Funding

Supports for this work by the National Natural Science Foundation of China under grant numbers 51705234, U1537202 and 2015B010132005, the Shenzhen Key Laboratory for Additive Manufacturing of High-performance Materials under grant number ZDSYS201703031748354, the Southern University of Science and Technology Presidential Postdoctoral Fellowship and the projected funded by China Postdoctoral Science Foundation under grant number 2017M612653 are gratefully acknowledged.