Determination of subsurface damage in Nd-doped phosphate glasses

Abstract

Nd-doped phosphate glasses have been widely used in high average power solid state lasers. Subsurface damage is one of the most important sources to reduce laser damage threshold which limits the useful output of high-power lasers. To eliminate subsurface damage (SSD), SSD detection must be done. In this paper, an instrument based on dimple method-a destructive method was developed to detect and measure subsurface damage produced in each fabrication process. Through the analysis of experimental data, we proved that there is a constant ratio between subsurface damage depth and surface roughness PV value during loose abrasive grinding of glass. We also correlate subsurface damage and surface roughness with the abrasive size. Experimental results show a good linearity. The ratio of subsurface damage depth and surface roughness PV value during grinding Nd-doped phosphate glasses was found to be 3.94±0.22. The relation between subsurface damage and abrasive size equals to 0.96±0.03. With this relation proved to be linear, subsurface damage depth can be valued from the abrasive size without destructing the sample. We also find that the linear constant of surface roughness and abrasive size is 0.25±0.02.With the constant, surface roughness can be estimated by abrasive size directly. Furthermore, the spindle speed and load were taken into account. All the results are helpful to estimate SSD and manufacturing high quality Nd-doped phosphate glasses. The way above can be applied for estimating SSD of other brittle material too.