Using NBOHC fluorescence to predict multi-pulse laser-induced damage in fused silica

We investigate the evolution of the fluorescence signal as function of repeated nanosecond laser pulses up to laser-induced damage in fused silica at 266 nm. We observed a maximum in the fluorescence spectrum at 664 nm linked to NBOHCs (Non-Bridging Oxygen Hole Centers). This peak increases with shot number for a fixed fluence until damage occurs. Thanks to the data from the in situ fluorescence measurements, we propose a new method to predict the occurrence of laser damage in high quality fused silica samples like Herasil©and Suprasil 1©. This new method allows to reduce drastically the time of test and the area under study that are required to record the reference data for damage occurrence. Furthermore we measured that the lifetime of the laser-induced modifications is about 2 h in Herasil.