Deterministic single shot and multiple shot bulk laser damage thresholds of borosilicate glass at 1.064 μm

Abstract

We measured the single-shot and multiple-shot optical breakdown thresholds leading to optical damage of borosilicate glass, specifically BK7 glass, at 1.064 μm. We used 8-ns, single-longitudinal-mode, TEM00 laser pulses tightly focused inside a BK7 glass window. The radius of the focal spot was measured using surface third harmonic generation; it is equal to 7.5 μm. With this tight focus, the laser power at the breakdown threshold of BK7 glass is below the SBS threshold, and the effect of self focusing is small. We found the single-shot and multiple-shots optical breakdown thresholds to be deterministic. At the single-shot damage threshold, the optical breakdown in BK7 glass occurs on the trailing edge of the laser pulse, in contrast to fused silica in which the breakdown always occurs at the peak of the laser pulse. However, the multiple-shot damage threshold of BK7 glass occurs at the peak of the last laser pulse. Our single shot damage threshold for BK7 glass is 4125 J/cm2, and our multiple shot damage threshold ranges from 3974 J/cm2 for 2-shot damage to 3289 J/cm2 for 31-shot damage. We also compare damage morphologies of BK7 glass with those of fused silica.