Research On Ultraviolet Nanosecond Laser Absorption And Damage Protection Technology Of Surface On Aluminum Alloy

The fusion energy generated by inertial confinement fusion(ICF)is favored by scientists because of its high efficiency,clean products and rich raw materials.It is not only expected to completely solve the energy crisis faced by human society,but also has important theoretical and practical significance for studying the evolution of matter under extreme conditions,such as the origin of the universe.During the transmission of high power laser beam in the optical component at the end of the inertial confinement fusion device,after the stray light dominated by ultraviolet nanosecond laser is reflected and converged on the aluminum alloy finish machined surface for many times,it will produce a convergence point with high fluence,which will directly damage the optical elements or the aluminum alloy surface,and the pollution particles generated will aggravate the damage of the optical elements,thus causing disastrous consequences to the optical system.Therefore,in order to solve the problem of ultraviolet nanosecond laser-induced damage in the final optical assembly,this paper proposes a new precision preparation method of aluminum alloy structure functional surface by in-depth studying the damage mechanism of aluminum alloy under the action of ultraviolet nanosecond laser.Based on aluminum alloy anodizing,cadmium selenide(Cd Se)nano light absorbing particles are added to the aluminum oxide array holes,and finally silicon dioxide film is used to seal the holes to improve the laser-induced damage threshold(LIDT),It can not only meet the requirements of high absorption rate of ultraviolet nanosecond laser and high laser-induced damage threshold,but also meet the requirements of precision assembly of aluminum alloy parts size accuracy and surface shape accuracy.The removal process of aluminum alloy material by ultraviolet nanosecond laser was studied.By systematically analyzing the heating mechanism and heat transfer mechanism of aluminum alloy under the action of ultraviolet nanosecond laser,the ultraviolet nanosecond laser ablation model of aluminum alloy is established,and the damage process of aluminum alloy under single and multiple irradiation of different laser fluences is simulated,and the effects of irradiation times and laser fluences on the ablation depths and thermal diffusion areas of aluminum alloy are obtained,which are compared with the experi mental results of laser damage,It is verified that the ablation model can effectively predict the ablation depths and thermal diffusion areas of aluminum alloy under ultraviolet nanosecond laser irradiation.At the same time,the absorption and laser-induced damage threshold of the aluminum alloy surface are obtained through experiments,which provides a theoretical basis for the subsequent research on improving the absorbance and laser-induced damage threshold.The process of light absorption and temperature rise of structural functional surface under ultraviolet nanosecond laser irradiation was studied.Based on the energy dissipation law,Planck’s law and Kirchhoff’s law generated by the Joule effect,combined with Poisson’s equation,Laplace’s equation and Green’s function,the light absorption and temperature distribution functions of nanoparticles in homogeneous media are derived.It is found that there is collective effects and thermal homogenization phenomenon in the process of temperature rise when ultraviolet nanosecond laser acts on multiple nanoparticles.A model of optical absorption and electromagnetic-thermal coupling of Al-based structural functional surface irradiated by ultraviolet nanosecond laser was established.The influence of structural parameters of Al-based structural functional surface and the diameter of Cd Se nanoparticles on the absorption rate and laser-induced damage threshold in the ultraviolet to visible band was studied by simulation.It lays a theoretical foundation for the design and preparation of Al-based structural functional surfaces with high absorption and excellent laser damage resistance ability to ultraviolet nanosecond laser.The preparation process of Al-based structural functional surface was studied.According to the simulation results of the interaction between the Al-based structure functional surface and ultraviolet nanosecond laser,the Al-based structure functional surface with different thickness was designed.The experimental equipments have been built,the experimental process has been determined,and the Al-based structural functional surfaces with different thickness have been prepared.The surface morphology,cross-section micro-nano structure characterization and structural composition analysis of the prepared Al-based structural functional surfaces have been carried out.The consistency between the optical absorption measurement results and the simulation prediction results of Al-based structural functional surfaces indicates that the simulation model can effectively predict the optical absorption rate.In addition,the experimental results of the absorption rate of the Al-based structural functional surface for the 300-600 nm nanosecond laser have exceeded 90%,realizing the high absorption rate of the ultraviolet nanosecond laser.The experimental study of the ultraviolet nanosecond laser laser absorption and damage protection on the surface of aluminum alloy was carried out.Ultraviolet nanosecond laser irradiation experiments were carried out on struct ural and functional surfaces with different thickness and different roughness substrates.It is found that the functional surface prepared after ultra-precision turning of aluminum alloy surface is more resistant to laser-induced damage than the structural and functional surface prepared by the same process without ultra-precision turning.The structural functional surface is prepared on the aluminum alloy substrate with the same surface roughness.Increasing the thickness of the functional surface can effectively improve the laser-induced damage threshold of the aluminum alloy.Therefore,the preparation method of Al-based substrate structure functional surface for ultraviolet nanosecond laser is proposed.After ultra-precision turning the aluminum alloy substrate and then prepare 20 μm thick Al-based structural functional surface can achieve high absorption of ultraviolet nanosecond laser and high laser-induced damage threshold,and meet the requirements of precision assembly in practical engineering.