Optical Methods for in-Process Monitoring of Laser-Matter Interactions

Laser micro−/nanofabrication is often carried out using short (nanosecond) or ultrashort (picosecond or femtosecond) pulsed lasers. Under extreme nonequilibrium conditions imposed by ultrashort laser irradiation, many fundamental questions concerning the physical origin of the material removal process remain unanswered. Therefore, it is necessary to accurately monitor the interaction between laser and matter. To investigate different kinds of laser-matter processes, such as laser-induced damage, plasma formation, phase transitions, and laser-induced chemical reactions at gas-solid and liquid-solid, many optical methods for in-process monitoring of laser-matter interactions have been developed. High-speed imaging is a valuable tool for investigations on laser processes. In this chapter, cutting-edge ultrafast dynamic optical imaging techniques for investigating the laser-matter interactions, including ultrafast pump-probe microscopy, laser holography imaging, and ultrafast continuous optical imaging, are introduced. Each technique is described in depth, beginning with its basic principle, followed by its representative applications in laser-material interaction. The consideration of temporal and spatial resolutions and panoramic measurement at different scales are the two major challenges for the in-process monitoring of laser-matter interactions. Hence, the prospects for technical advancement in this field are discussed.