Mechanism of laser damage induced by inclusions in fused silica

A model was developed for the description of inclusion-induced damage in fused silica by nanosecond-pulse laser at 355 nm. We calculated the temperature of impurity particles with their sizes increasing, and obtained the correlation between the critical fluence and particle radius through Mie theory and heat equation. Moreover, the size at which fused silica damage could be induced easily was discussed for each particle. We got the curves of laser damage probability for samples from the results of damage tests at last. Both the calculation and the experiment show that, by absorbing the energy of laser, with the particle radius increasing, the temperature in particle edge increases first and then decreases. Hence, only a certain range of particles can initiate damage of fused silica. The particles whose radius corresponds to critical fluence most likely cause breakdown of fused silica. The probability of damage on the fused silica sample etched decreases as its impurity density at surface decreases, thus improving the damage threshold of the fused silica.