Monitoring method for femtosecond laser modification of silicon carbide via acoustic emission techniques

摘要

The interaction between femtosecond laser (fs-laser) and silicon carbide (SiC) is complex, and it will form various modified surface structures related to the physical phenomena of melting, evaporation and plasma. Acoustic emission (AE) is used as a non-destructive real-time detection method that can capture local changes in materials and monitor the process of fs-laser modification of silicon carbide. In this paper, AE analysis, including single parameter analysis, correlation analysis and short time Fourier transform (STFT), are used to analyze the process of laser modified SiC. The relationships between material removal, surface structure characteristics, surface defects and AE signals are established. Results indicate that the material removal of SiC surface ablated by fs-laser increases with the laser fluence, which results in the increase of MARSE and high-frequency component scatters (300 similar to 400 kHz) as well as the dramatic change of Root Mean Square (RMS). The different surface structures formed on the SiC are classified and characterized by AE signals. The similar modified surface structure causes signal scatter to overlap, proving that the clustering characteristics of the AE signals are closely related to the modified surface structures. The color change of frequency components in the STFT spectrum is related to the surface defects generated in the process of fs-laser modification. The larger the laser fluence irradiate on the area, the more evenly the color are distributed.