The cleaning mechanism of optical surface particle contaminants in the light pneumatic tube was simulated based on the static equations and JKR model. Cleaning verification experiment based on air knife sweeping system and on-line monitoring system in high power laser facility was set up in order to verify the simulated results. Results showed that the removal ratio is significantly influenced by sweeping velocity and angle. The removal ratio can reach to 94.3% by using higher input pressure of the air knife, demonstrating that the air knife sweeping technology is useful for maintaining the surface cleanliness of optical elements, and thus guaranteeing the long-term stable running of the high power laser facility.
The outgassing characteristic of the silicone rubber which is the main material of non-metallic materials in high power laser system was studied，outgassing rates of the silicone rubber and the baked-out silicone rubber which was performed at 80°C4 hours were measured by the constant volume process method，and outgassing properties of them were analyzed by the quadrupole mass spectrometer. The results show that the outgassing rate of the silicone rubber and the baked-out silicone rubber is 2.69×10<sup>-7</sup> Pa·m<sup>3</sup>s<sup>-1</sup>cm<sup>-2</sup> and 6.47×10<sup>-8</sup> Pa·m<sup>3</sup>s<sup>-1</sup>cm<sup>-2</sup> ， respectively. All of them give out condensable volatile matter in vacuum. The outgassing rate and condensable volatile matter of the baked-out silicone rubber are less an order of magnitude compared with the silicone rubber, and the outgassing rate of the silicone rubber is less than 1×10<sup>-7</sup> Pa·m<sup>3</sup>s<sup>-1</sup>cm<sup>-2</sup>, which is fit for non-metallic material of the high power laser system. This paper also discusses the method of reducing the outgassing rate and condensable volatile matter of the silicone rubber in high power laser system.
The residual stress field of fused silica induced by continuous wave CO2 laser irradiation is investigated with specific photoelastic methods. Both hoop stress and axial stress in the irradiated zone are measured quantitatively. For the hoop stress along the radial direction, the maximum phase retardance of 30 nm appears at the boundary of the laser distorted zone (680-μm distance to center), and the phase retardance decreases rapidly and linearly inward, and decreases slowly and exponentially outward. For the axial stress, tensile stress lies in a thin surface layer (<280 μm) and compressive stress lies just below the tensile region. Both tensile and compressive stresses increase first and then decrease along the depth direction. The maximum phase retardance induced by axial tensile stress is 150 nm, and the maximum phase retardance caused by axial compression stress is about 75 nm. In addition, the relationship between the maximum axial stress and the deformation height of the laser irradiated zone is also discussed.
The laser-induced bulk damage and stress behaviors of fused silica are studied by using a neodymium-doped yttrium aluminum garnet laser operated at 1064 nm with pulse width of 11.7 ns. Three zones of bulk damage are defined: columned cavity zone, compacted zone, and crack zone. The damage morphology and stress distribution are characterized by a three-dimensional digital microscope and a polarizer stress analyzer. The results show that the stress in the columned cavity zone and compacted zone is approximately zero. From the laser beam center to fringe, both tensile and compressive stresses in the crack zone increase abruptly and linearly and then decrease exponentially. Thermal annealing is used to prove the phase retardation caused by the residual stress. The formation mechanism of bulk damage is also discussed.
Damage sites as large as 600 μm in fused silica surface were successfully mitigated with a new protocol by hydrofluoric acid (HF) etching combined with carbon dioxide laser treatment. The damage sites were first etched in 40% HF solution to blunt the fractures, and then the etched damage sites were smoothed with a CO2 laser. It has been found that the etching rate of damaged material in the lateral direction is larger than in the longitudinal direction; thus, an optimized etching time was chosen to etch the damage sites based on the etching ratio. Three types of damage test methods were used to confirm the mitigation efficiency of the protocol. The results indicate that the damage resistance capability of mitigated sites can recover to the level of pristine substrate.
The dynamics of 355-nm laser ablation on fused silica were studied by instantaneous scattering pulse
measurement and a time-resolved shadowgraph imaging. The sharp increase of scattered light of pumped
pulse is assumed to be the damage precursor, therefore, the damage start nearly at the peak of the
pumped pulse. The plasmas flash due to ion-electron recombination occurred about 21ns after the
peak of pumped pulses. The propagating shock wave and ejected material to the air were imaged by
shadowgraphic technology. The damage process of fused silica under UV laser ablation was also