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Growth mechanism of laser-induced damage in fused silica

Growth of laser induced damage on the surface of fused silica plays a major role in determining the optics lifetime in high power laser system. Previous studies proved that the size of the crater increased under successive laser shots, but that of the gray haze and CO2 laser mitigation spot remained constant. In this study, Scanning electron microscopy (SEM), focus ion beam (FIB) and profiler were applied to observe their vertical and horizontal cross sections. Energy dispersive spectrometers (EDS) micro-analysis technique and fluorescent microscopy were used to detect the differences of chemical composition and molecular structure among the three. Results showed that the absorbing defect and crack was found in the crater, which did not exist in the gray haze and mitigation spot. Finite difference time domain (FDTD) was applied to calculate the light intensity distribution. It's found that the peak light intensity around the crater was much higher. Based on the above analysis, a growth mechanism of laser induced damage in fused silica was proposed.