A 4-Dimensional Spectroscopic Diagnostic Method for Laser-Induced Plasma Using Femtosecond Filamentation Probe

Understanding the spatiotemporal evolution of species in laser-induced plasma (LIP) is essential for LIP applications, such as laser fusion, extreme ultraviolet, laser processing, and LIP spectroscopy. However, common LIP diagnostics only allow for capturing the 2-dimensional characteristics of LIPs and suffer from spatiotemporal integral effects. These effects obscure the large gradients in the physical and chemical properties of LIPs over time and space. Therefore, in this work, we introduce for the first time a 4-dimensional ultrafast spectroscopic diagnostic method, that is, a temporal dimension and 3 spatial dimensions, for the spatiotemporal evolution of species in LIP using femtosecond laser filamentation. By virtue of the extremely high power density in the filamentation probe, species within the plasma are re-excited, and femtosecond-laser-induced breakdown spectroscopy (FIBS) for the local species is obtained. It follows from the FIBS that the spatiotemporal distributions of Fe, Al, and Mn in the vertical plane of plasmas with a thickness of about 100 μm are mapped, effectively avoiding spatiotemporal integral effects. The fractionation of the elements in the LIP is obtained, showing that the Al element is mainly distributed in the outer shell and the tail of the plume. In contrast, the Mn element is mostly distributed in the inner shell of the plume. Additionally, the self-absorption effects on diagnosis through FIBS in the horizontal direction are investigated. This study provides a novel and important avenue to diagnose LIP at a high spatiotemporal resolution in a 4-dimensional manner, exhibiting great potential in LIP applications.