Thermal behavior of materials in laser-assisted extreme manufacturing: Raman-based novel characterization

Laser-assisted manufacturing (LAM) is a technique that performs machining of materials using a laser heating process. During the process, temperatures can rise above over 2000 ℃. As a result, it is crucial to explore the thermal behavior of materials under such high temperatures to understand the physics behind LAM and provide feedback for manufacturing optimization. Raman spectroscopy, which is widely used for structure characterization, can provide a novel way to measure temperature during LAM. In this review, we discuss the mechanism of Raman-based temperature probing, its calibration, and sources of uncertainty/error, and how to control them. We critically review the Raman-based temperature measurement considering the spatial resolution under near-field optical heating and surface structure-induced asymmetries. As another critical aspect of Raman-based temperature measurement, temporal resolution is also reviewed to cover various ways of realizing ultrafast thermal probing. We conclude with a detailed outlook on Raman-based temperature probing in LAM and issues that need special attention.