Abstract
Laser-induced damage on fused silica optics remains a major issue that limits the promotion of energy output of large laser systems. Subsurface impurity defects inevitably introduced in the practical polishing process incur strong thermal absorption for incident lasers, seriously lowering the laser-induced damage threshold (LIDT). Here, we simulate the temperature and thermal stress distributions involved in the laser irradiation process to investigate the effect of impurity defects on laser damage resistance. Then, HF-based etchants (HF:NH4F) are applied to remove the subsurface impurity defects and the surface quality, impurity contents and laser damage resistance of etched silica surfaces are tested. The results indicate that the presence of impurity defects could induce a dramatic rise of local temperature and thermal stress. The maximum temperature and stress can reach up to 7073 K and 8739 MPa, respectively, far higher than the melting point and compressive strength of fused silica, resulting in serious laser damage. The effect of impurity defects on laser damage resistance is dependent on the species, size and spatial location of the defects, and CeO2 defects play a dominant role in lowering the LIDT, followed by Fe and Al defects. CeO2 defects with radius of 0.3 μm, which reside 0.15 μm beneath the surface, are the most dangerous defects for incurring laser damage. By HF acid etching, the negative effect of impurity defects on laser damage resistance could be effectively mitigated. It is validated that with HF acid etching, the number of dangerous CeO2 defects is decreased by more than half, and the LIDT could be improved to 27.1 J/cm2.
Highlights
In order to achieve clean and sustainable energy resources, high-power laser systems have been developed worldwide for pursuing inertial confinement fusion (ICF), such as the National IgnitionFacility (NIF) in the United States [1,2], the Laser MegaJoule (LMJ) in France [3], the High Power laserEnergy Research facility (HiPER) in Europe [4] and the ShenGuang (SG)-III laser facility in China [5].To obtain the extremely high pressure and temperature required for ICF ignition, a huge amount of large-aperture optics with high precision surfaces are required to temporally, spatially and spectrally control the laser beams
In order to figure out the most dangerous impurity defect to the laser damage resistance of fused silica, we investigate the temperature caused by impurity defectsresistance with various
It is shown that the contents of most of the impurity defects are effectively lowered by impurity defects could be removed by HF-based etchants (HF) acid etching and the heat absorption caused by impurity acid etching, especially for the Ce impurity content largely descends wt % to defects would be greatly mitigated to defect, improvewhose the laser damage resistance offrom fused7.45 silica
Summary
In order to achieve clean and sustainable energy resources, high-power laser systems have been developed worldwide for pursuing inertial confinement fusion (ICF), such as the National Ignition. The temperature and thermal stress distributions inside fused silica caused by impurity defects are investigated to figure out the most dangerous species and size range of impurity defects in decreasing the laser damage resistance of silica optics This part of work could provide further understanding of the laser-induced damage mechanisms on optical components, which are beneficial to the surface/subsurface quality evaluation and SSD removal of ultra-precision fabricated fused silica optics. To alleviate the effect of SSD defects on the laser damage resistance of fused silica optics, many engineering techniques (e.g., hydrofluoric HF acid etching [26,27,28], ultraviolet or CO2 laser preprocessing [8,29], plasma etching [30], and magneto-rheological finishing (MRF) [31], etc.) have been developed and applied in the actual preparation processes of high-quality silica surfaces. The etching rate, impurity contents, surface quality and laser damage resistance of etched silica samples are thoroughly investigated and analyzed to validate the role of the HF acid etching technique in removing the subsurface impurity defects and promoting the laser energy capacity of fused silica
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
