Femtosecond laser technology has attracted significant attention from the viewpoints of fundamental and application, especially femtosecond laser processing materials presents the unique mechanism of laser-material interaction. Ultrafast lasers can change the states and properties of materials through interactions with them, and they can be used to control the processing of materials from the micrometer scale down to the nanometer scale or across scales. Under the extreme nonequilibrium conditions imposed by femtosecond laser irradiation, many fundamental questions concerning the physical origin of the material removal process remain unanswered. In this review, cutting-edge ultrafast dynamic observation techniques for investigating the fundamental questions, including time-resolved pump-probe shadowgraphy, ultrafast continuous optical imaging, and four-dimensional ultrafast scanning electron microscopy are comprehensively surveyed. Each technique is described in depth, beginning with its basic principle, followed by a description of its representative applications in laser-material interaction and its strengths and limitations. The consideration of temporal and spatial resolutions and panoramic measurement at different scales are two major challenges. To address the challenges, the article outlines the development and prospects for the technical advancement in this field. The multiscale observation system could be used to determine the evolution of the structure and properties from electron ionization (femtosecond-picosecond scale) and material phase transition (picosecond-nanosecond scale) in a manufacturing activity in which the observations of multiscale processes have high spatial-temporal resolution, which would bring about a paradigm shift in femtosecond laser manufacturing.
Dr. Baoshan Guo
is an Associate Professor in the School of Mechanical Engineering at Beijing Institute of Technology. He received his Ph.D. in photoelectronics from the Institute of Semiconductor of Chinese Academy of Sciences. He has authored 1 book, over 40 journals and conferences papers. His research interests include new methods of ultra-fast laser micro/nano fabrication and applications, plasmonic dynamics and devices, plasmonic enhanced coherent Anti-Stokes Raman scattering microscopy, stimulated Raman scattering, ultrafast spectroscopic and imaging technology based on optical time-stretch, amplified dispersive Fourier transformation, and Sequentially Timed All-optical Mapping Photography.
Dr. Jingya Sun
is an Associate Professor in the School of Mechanical Engineering at Beijing Institute of Technology. She received a doctorate in Physics from National University of Singapore in 2012. For many years, she is dedicated to the research of ultrafast carrier dynamics by using four-dimensional ultrafast electron microscopy, and to study the dynamic processes (e.g., electron ionization and decay, laser-induced plasma dynamics and shockwave expansion) of various materials in femtosecond laser manufacturing by using time-resolved pump-probe shadowgraphy techniques.
Prof. Yongfeng Lu
is a Lott Distinguished University Professor in the Department of Electrical and Computer Engineering at University of Nebraska-Lincoln. He received his Ph.D. from Osaka University of Japan in 1991. He is the Fellow of American Optical Society, International Society of Optical Engineering, and American Laser Society. He is former Chairman of the American Laser Association and Winner of the Schawlow Award. He has published over 300 papers in mainstream international journals. His research interests include Carbon materials, Nanophotonics, Optical spectroscopy and imaging, Nanoscale laser material processing and characterization, Laser-assisted nanoimprinting, 2D and 3D nanomanufacturing employing scanning probe microscope, Surface cleaning and drying, Laser-assisted materials synthesis and processing, Molecular Level Surface Drying for Nanoelectronics, Supercapacitors, and Laser-assisted chemical vapor deposition.
Prof. Lan Jiang
is a Changjiang Professor in the School of Mechanical Engineering at Beijing Institute of Technology, and a Part-time Professor (Russell Severance Springer Professor) at University of California at Berkeley. He is the Fellow of American Society of Mechanical Engineering, American Society of Optics, and International Society for Nanomanufacturing. He is the director of National Innovation Center for Complex Micro-structure Machining Technology of China, and the director of Non-Traditional Micro/Nano Manufacturing Key Laboratory of Ministry of Industry and Information Technology of China. He is an internationally recognized leader in laser micro/nano manufacturing, to which he has made significant contributions. He has won the Second Prize of National Natural Science Award of China, Ho Leung Ho Lee Foundation Innovation Prize, and National Outstanding Young Scientists Award of China. He has published over 250 papers in mainstream international journals, with an H-index of 45. Many of his methodologies have been adopted by major national projects and industry.