Laser durability evaluations of silica glass at 1064 nm and 213 nm

Nd:YAG lasers are easy to operate, and are used in material processing applications. Because they are high-power lasers, optical materials with high laser durability are required for their optical systems. One of the commonly used materials for high-power lasers is silica glass. The silica glass has not only high laser durability but also high transmittance from the UV region to the IR region. In this study, we evaluated the laser durability by measuring laser-induced bulk damage threshold (LIDT) of silica glasses at 1064 nm and 213 nm, as the one of the key indexes for laser durability. We obtained following results. First, at 1-on-1 LIDT measurements, the LIDTs of samples were almost the same at each wavelength. On the other hand, the LIDT results were different depending on the sample at 213 nm as well as at 355 nm and 266 nm. The more hydroxyl concentration the silica glass had, the lower laser durability the silica glass had. However the difference of LIDT results at 1064 nm was also small at 10000-on-1 LIDT. Second, the silica glass which includes chlorine had lower durability even if its hydroxyl concentration was very low. Finally, hydrogen concentration dependency of the durability was varied by the hydroxyl content. If the content of hydroxyl was ≤10 ppm, LIDT became lower as hydrogen concentration increased. On the other hand, if it was equal to 30 ppm, LIDT became higher as hydrogen concentration increased. Based on these results, we can improve laser durability of silica glass at 213 nm by either reducing hydroxyl and chlorine or controlling hydrogen concentration. We can also select an appropriate silica glass in accordance to use.