Optical Components Laser-induced Injury

High power laser-induced damage of optical elements is one of the main limiting factors for ICF laser driver development to higher and stronger, driven by the economic benefits and technical development, it will be a continuing challenge. Damage morphology is the external manifestation of the mechanism of injury, plasma and shock wave generation and development is the main reason of the damage and damage growth. Study of the morphology of the strong laser induced damage and the ultrafast kinetic characteristics of the damage process, analysis the law of the strong laser induced damage, helps us to understand the physical meaning of the laser-induced material damage, helps us to understand the physical meaning of the laser-induced material damage, master the physical mechanism and law of damage, has practical significance to improve the processing of optical components, to increase the useful life, to reducing the running costs of the high-energy laser systems and increase load capacity.In this paper, the Nd:YAG nanosecond laser induced damage of the optical components are studied. The main idea is based on the1064nm,532nm and355nm three wavelength nanosecond laser induced optical element initial damage and damage growth morphology, combining with ultrafast time-resolved method of the shadow map, obtaining the time-resolved images of the process of generation and development of shock waves and plasma on the input-surface, output-surface and in material in fused silica, and analysis the laws of physics and the mechanism of optical component damage induced by nanosecond laser.First of all, a brief description of the pulsed laser and material interaction theory and the physical mechanism of optical element damage induced by high power laser, analyzed the methods and ways of improving the laser damage resistance of optical components. Under the nanosecond laser irradiation, the surface and sub-surface defects remains by the processing and use of the process is the direct cause component damage. Laser induced damage of the optical component is a complex process involving photothermal, photoacoustic, optoelectronics, laser parameters, material properties, linear and nonlinear effects, plasma and shock wave and many other physical effects. The major damage mechanism are:heating by the absorption of scratches、cracks、impurities and other defects, ultrasonic induced damage by Stimulated Brillouin Scattering, avalanche ionization and multiphoton ionization damage, the damage caused by the nonlinear self-focusing. In the general case, typically damage is the results of many of these mechanisms together and promotes each other. Experimental study of1064nm,532nm and355nm three-wavelength laser induced initial damage and growth damage of surface and material in fused silica, to study behavior which under multiple wavelengths combination on laser-induced damage, comparison and analysis of each wavelength laser initial damage and damage growth laws and mechanisms of optical components. The results show that:the surface impurities and defect is the main cause of optical components surface damage induced by nanosecond laser, the development and nature of plasma and shockwave in material and air led to the huge difference of the front and back surfaces of the initial damage and damage growth. Corresponding to different laser wavelengths, the cracks and materials in damage crater will effect damage growth, self-focusing filamentation damage is according to point defects too. For different laser wavelength, the type and number density of damage pioneer has huge difference. Laser preparation condition can improve the damage threshold, damage accumulation effect are more obvious under the ultraviolet laser irradiation. Under the two wavelengths laser simultaneously irradiation, at first, impurities and defects by the short wavelength laser ionization, and then, the free electrons generated by the ionizing greatly enhance the absorption of long wavelength laser.The dynamic process of nanosecond laser induced damage of fused silica’s input-surface, exit-surface and bulk in air was investigated by ultrafast time-resolved shadowgraphs. The comparison and analysis of the damage mechanism among the input-surface, exit-surface and bulk were performed. In the input-surface, generation and development process of plasma and shock wave were observed in air and materials. Three stress waves were observed in material under the sub-nanosecond laser, and the bulk damage was observed near the input-surface. In the output-surface, in addition to the shock wave formation and development process is observed, but also the process of material ablation and explosive phase ejections were obtained. In the bulk, the results show that both the self-focusing and defect’s absorption answerable for the damage, damage induced by the defect’s absorption maybe have temporal difference. The present research is instructive to understand the laser-induced damage mechanism of the fused silica.