Laser-damage characteristics of Nd:glass active mirrors

The active-mirror architecture is widely used in high-power laser systems. In this study, the laser-damage characteristics of Nd:glass active mirrors are investigated. They are exposed to nanosecond 1064 nm laser incident from the Nd:glass. The laser-induced damage thresholds (LIDTs) of the coated sides are lower than those of the uncoated sides. The LIDT of the active mirror whose substrate is manually scrubbed is lower than that of one whose substrate is ultrasonically cleaned. Analysis shows that the absorbing surface defects on the manually scrubbed Nd:glass surface are responsible for the lower LIDT of the active mirror prepared via manual scrubbing, while the subsurface defects in the ultrasonically cleaned Nd:glass substrate are the main reason for the damage of the active mirror prepared via ultrasonic cleaning. The strong standing-wave electric field near the interface between the coating and the Nd:glass substrate is another factor affecting the damage of the active mirror.