Multipulse degradation of fused silica surfaces at 351 nm

We investigate the multipulse degradation of fused silica surfaces exposed at 351 nm for up to 109 pulses at pulse fluences greater than 10 J/cm2. In vacuum, the transmission loss increases as a function of the number of shots at low pulse intensity. However, as the pulse intensity increases, the transmission loss decreases and is not measureable above a certain intensity. Transmission loss is highest when measured at shorter wavelengths, and decreases towards the IR. Absorption is the primary mechanism that leads to transmission loss and is from photo-reduction of the silica surface.