Characterization of artificial indentation defects in fused silica surface and its damage performance under 355 nm nanosecond laser

The mechanical defect of fused silica caused by polishing process is the main reason for the decrease of laser-induced damage threshold (LIDT). In this paper, the artificial indentation was used to alternatively study the feature of machining defects and its laser damage properties. The Vickers indentation on fused silica surface were characterized with SEM, photoluminescence (PL) spectroscopy and photothermal absorption. Combined with hydrofluoric (HF) acid etching, the relationship between indentation intrinsic feature and LIDT was revealed. Crack and brittle fracture in the indentation contain various point defects, cause PL intensity and photothermal absorption increasing. By use of time resolved pump–probe imaging technology, we confirmed that energy absorption process during laser damage mostly initiates at the crack region. Shallow etching with HF acid (about 150 nm depth etched) removes a certain material and effectively reduces the density of point defects in the superficial layer of the indentation, consequential reduces the photothermal absorption and PL intensity, and finally improves LIDT.