Yayun Ye

Surface Contaminant Control Technologies to Improve Laser Damage Resistance of Optics

The large high-power solid lasers, such as the National Ignition Facility (NIF) of America and the Shenguang-III (SG-III) laser facility of China, can output over 2.1 MJ laser pulse for the inertial confinement fusion (ICF) experiments. Because of the enhancement of operating flux and the expansion of laser driver scale, the problem of contamination seriously influences their construction period and operation life. During irradiation by intense laser beams, the contaminants on the metallic surface of beam tubes can be transmitted to the optical surfaces and lead to damage of optical components. For the high-power solid-state laser facilities, contamination control focuses on the slab amplifiers, spatial filters, and final-optical assemblies. In this paper, an effective solution to control contaminations including the whole process of the laser driver is put forward to provide the safe operation of laser facilities, and the detailed technical methods of contamination control such as washing, cleanliness metrology, and cleanliness protecting are also introduced to reduce the probability of laser-induced damage of optics. The experimental results show that the cleanliness level of SG-III laser facility is much better to ensure that the laser facility can safely operate at high energy flux.

Investigation of Control of Residual Stress Induced by CO2 Laser-Based Damage Mitigation of Fused Silica Optics

A CO2 laser-based annealing technique for the mitigation of damaged sites of fused silica is studied to suppress the residual stress left on the surface. The laser annealing by a linear decrease of the CO2 laser power effectively reduces the residual stress. The residual stress of mitigated sites is characterized by polarimetry, the reduction of the maximum retardance around the mitigated sites with the exposure time of laser annealing fits a stretched exponential equation, and the maximum retardance with optimal laser annealing is reduced (36 ± 3)% compared to that without laser annealing. The residual stress regions are destructively characterized by introducing damage. The critical size of damage leading to fracture propagation for the mitigated sites without laser annealing is in the range of 120~230 μm, and the corresponding critical size of damage for the mitigated sites with laser annealing is larger than 600 μm. According to the relationship between maximum damage size and critical stress, the residual stress without laser annealing is in the range of 28–39 MPa and the residual stress with laser annealing is less than 17 MPa. These results indicate that the CO2 laser-based annealing technique has a positive effect on the control of residual stress induced by CO2 laser-based damage mitigation.

Preparation of broadband absorption ceramic coatings by using plasma electrolytic deposition

Two types of black ceramic coatings with high spectrum absorptivity were prepared on Al alloy substrate by using plasma electrolytic deposition method. The spectrum absorption properties of coatings were tested by using 355 nm ultraviolet laser pulses. Particle counter device was employed to collect and analyze the particles formed during the irradiation process. Experimental results showed that the coatings have porous structures. The sample coatings 1 and 2 have thickness of 120 μm and 60 μm with holes’ diameter of about 70 μm and 15 μm, respectively. The coating 1 is mainly composed of Al2O3 and SiO2 while coating 2 consists of Al2O3. The reflectivity of both coatings is much lower than that of Al alloy substrate. The absorptivity of samples 1 and 2 is about 99.88% and 99.92% for wavelength from 300 nm to 800 nm. The mechanisms of spectrum absorption were also explored.

The formation of periodic micro/nano structured on stainless steel by femtosecond laser irradiation

Stainless steel surface was irradiated by linear polarized laser (800 nm, 35 fs, 4 Hz and 0.7 J/cm2) with different pulse numbers. Environmental scanning electron microscope (ESEM/EDS) was used for detailed morphology, microstructure and composition studies. The wettability of irradiated steel surface was tested by Interface Tensiometer JC-2000X and compared with untreated stainless steel. Results showed that micro/nanostripes with different periods were formed. The period increased with the increasing pulse numbers from 450 nm for 90 pulses to 500 nm for 180 pulses. The orientation of those stripes was parallel with the laser beam polarization. Nanoparticles were observed on those periodic structures. EDS indicated that the atomic ratio of Cr increased and the atomic ratios of Fe and Ni decreased after laser irradiation, which may enhance the corrosion resistance due to the Cr-rich layer. The prepared structure exhibited hydrophobic property without further treatment. The formation mechanism of micro/nanoperiodic structures was also explored.

Laser cleaning of the contaminations on the surface of tire mould

During the manufacturing of tires, surface pollutants on tire mould will lead to the production of unqualified tires. Tire moulds need to be regularly cleaned. Laser cleaning is recognized as a non...