Advances and opportunities of ultrafast laser synthesis and processing
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Introduction Our understanding of ultrafast laser interactions with materials has come a long way since MRS Bulletin published a theme issue on the topic 10 years ago.1 The most significant advances have resulted from our continued understanding of the atomistic mechanisms and dynamics that control the material response. Both theoretical and experimental work have contributed to these advances that are reviewed in the articles in this issue. There is still much to learn about fundamental laser–solid interactions. We have only just scratched the surface, and tremendous opportunities exist to exploit the extreme conditions that are attainable with ultrafast laser interactions. New computational tools and powerful parallel processing ability will enable us to tackle time-dependent excited-state phenomena that are far from the ground-state Born–Oppenheimer surface. Real opportunities in laser–solid interactions exist for the following reasons: (1) The ultrafast time scale can limit the material interaction with the laser field to only electronic excitation and leave the remaining ions with their roomtemperature velocity distribution; (2) the extreme conditions that a material can be brought to in temperature and pressure; (3) control of defect production at relatively low fluence; (4) capability of three-dimensional (3D) micro- and nanoprocessing; and (5) new opportunities in new materials classes, including biological and carbon-based materials.
A steady stream of applications has already resulted from our fundamental understanding of ultrafast laser–solid interaction. Some of these have achieved mainstream industrial adoption (e.g., femtosecond [fs] laser surgery2). If anything can be said about the 10 years since the last MRS Bulletin theme issue on ultrafast lasers and materials research, it is that there has been an explosion in the fundamental understanding (see the Shugaev et al. and Abere et al. articles in this issue), applications (see Jiang et al. in this issue), and technologies to develop tools for those applications (see Mottay et al. in this issue). Emerging nanoprocessing applications could take advantage of the high-resolution feature fabrication offered by ultrafast lasers coupled to scanning probes.3 Many challenges, however, remain before we can achieve the significant impact that ultrafast laser synthesis and processing promises. Many applications cannot be implemented on a commercial scale until higher average power lasers and, more importantly perhaps, both high peak power and high average power lasers with high stability and reliability are available. Current experimental and computational tools to study the earliest time scales continue to develop, but still need significant improvement. It has been clear throughout the history of ultrafast laser interactions of materials that what happens during the first few picoseconds (ps) does not stay in the first few ps. Rather, these short-lived events dictate a
Steven M. Yalisove, Materials Science and Engineering Department, University of Michigan, USA; smy@
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