During femtosecond laser fabrication, photons are mainly absorbed by electrons, and the subsequent energy transfer from electrons to ions is of picosecond order. Hence, lattice motion is negligible within the femtosecond pulse duration, whereas femtosecond photon-electron interactions dominate the entire fabrication process. Therefore, femtosecond laser fabrication must be improved by controlling localized transient electron dynamics, which poses a challenge for measuring and controlling at the electron level during fabrication processes. Pump-probe spectroscopy presents a viable solution, which can be used to observe electron dynamics during a chemical reaction. In fact, femtosecond pulse durations are shorter than many physical/chemical characteristic times, which permits manipulating, adjusting, or interfering with electron dynamics. Hence, we proposed to control localized transient electron dynamics by temporally or spatially shaping femtosecond pulses, and further to modify localized transient materials properties, and then to adjust material phase change, and eventually to implement a novel fabrication method. This review covers our progresses over the past decade regarding electrons dynamics control (EDC) by shaping femtosecond laser pulses in micro/nanomanufacturing: (1) Theoretical models were developed to prove EDC feasibility and reveal its mechanisms; (2) on the basis of the theoretical predictions, many experiments are conducted to validate our EDC-based femtosecond laser fabrication method. Seven examples are reported, which proves that the proposed method can significantly improve fabrication precision, quality, throughput and repeatability and effectively control micro/nanoscale structures; (3) a multiscale measurement system was proposed and developed to study the fundamentals of EDC from the femtosecond scale to the nanosecond scale and to the millisecond scale; and (4) As an example of practical applications, our method was employed to fabricate some key structures in one of the 16 Chinese National S&T Major Projects, for which electron dynamics were measured using our multiscale measurement system.
Bibliographical noteFunding Information:
This research was supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 90923039, 91323301, 50705009, 51105037, 51322511 and 51025521), National Basic Research Program of China (973 Program) (Grant No. 2011CB013000), the 863 Project of China under Grant No. 2008AA03Z301, the Cultivation Fund of the Key Scientific and Technical Innovation Project, Ministry of Education of China (No. 708018), the 111 Project of China (Grant No. B08043), Multidisciplinary University Research Initiative (MURI) program of USA under Grant No. N00014-05-1-0432 and National Science Foundation of USA under Grant No. 0423233. We thank Prof Xin Li, Prof Jie Hu, Prof Sumei Wang, Prof Xiaowei Li, Prof Jingya Sun, Prof Jianfeng Yan, Dr Xiaoxing Su, Dr Weina Han, Dr Qingsong Wang, Dr Zhitao Cao, Mr Zhi Wang, Dr Changji Pan, Dr Peng Ran and Dr Pei Zuo for discussing, revising and proofreading this manuscript.
© The Author(s) 2018.
- electrons dynamics control
- femtosecond laser
- micro/nano fabrication
- pulse shaping