Laser-induced damage thresholds in SiO₂-coated aluminum mirrors under various ultrashort pulse widths

The influence of laser temporal parameters on the laser-induced damage threshold (LIDT) is particularly complex due to the variation and uncertainty in damage mechanisms associated with different pulse widths, especially in the range that bridges transitional damage mechanisms. Metallic mirrors are ideally suited for ultrashort pulse optical systems owing to their broad spectral range. A comprehensive understanding of the damage behavior of metallic mirrors under ultrashort pulse widths is crucial for optimizing their performance and manufacturing processes. Consequently, a laser damage testing platform was established in the laboratory to conduct 1-on-1 and area-based damage testing method on SiO₂-coated aluminum mirrors, covering a pulse width range of 0.2 to 11 ps. The experimental results revealed two transitions in the LIDT from 0.2 to 11 ps. Specifically, within the 0.3 to 8 ps pulse width range, the LIDT inversely correlated with the pulse width, adhering to a power-law relationship. Conversely, for pulse widths below 0.3 ps and between 8 and 11 ps, the LIDT positively correlated with the pulse width. Observations using optical microscopy and scanning electron microscopy (SEM) exhibited the damage morphology at different pulse widths, which indicated that damage initially occurred in the SiO₂ dielectric film on the sample surface, demonstrating a transition in the laser damage mechanism across the experimental pulse width range.