The effect of deep HF etching on the surface quality and figure of fused silica optics has been investigated systematically. Fused silica samples (100 mm in diameter x 10 mm thick) were manufactured using the conventional grinding and polishing process. These processed samples are etched with different removal depth. Initially, the surface quality of fused silica samples is characterized in terms of surface roughness and surface defects. Many digs not more than 1μm deep are emerged which originates from the micron grinding cracks and crack pits. These digs worsened the surface roughness and frosted the sample. While submillimeter subsurface damage exposed through etching appear as sparkling dots under the high power lamp. The average total length of millimeter scratches on single surfaces is over 200 mm. Not all millimeter scratches could be exposed until removal depth of up to 2 μm. Finally, the surface figure behavior during deep etching has also been figured out. Etching on the edge of the upper surface of samples placed horizontally went faster than on the inside parts. The surface of samples placed vertically assumed a more complicated removal distribution, which can be both explained in terms of "fringe tip effect". For the change of surface figure PV, the initial surface figure feature plays an important role as well as the etching removal distribution.
The low surface laser damage threshold of fused silica components in high power laser systems such as NIF restricts the improvement of the output fluence of those systems. Once damage is initiated and grows under subsequent laser shots, the components will go unusable. Subsurface damage (SSD) introduced during manufacturing has been identified as a main damage initiator. A good knowledge of SSD and how manufacturing influences it is essential to optimize manufacturing processes for damage free optics. Using the magneto-rheological finishing (MRF) wedge technique of better accuracy attributed to a tip, we have characterized the subsurface damage on fused silica optical surfaces ground with loose Al2O3 abrasives of different sizes. Larger abrasives generates longer cracks and the number density of cracks decreases sharply with the depth for each size. Rogue particles account for the occurrence of trailing indent scratches. Addition of rogue abrasives into relatively small base abrasive extends SSD more deeply than that induced by rogue abrasives alone. The linear model, with the proportional coefficient 3.511, fits the relationship between SSD depth and surface roughness (SR) better than the quadratic polynomial one. We believe SSD depth relates to SR more statistically than following some specified physical law. The linear relationship between SSD depth and the abrasive size was also established. The abrasive size turned out not to be as a good indictor of SSD depth as SR.