Study On The Thermal Destruction Mechanism Of Optical Components Induced By High Power Laser

With the development of high-power laser technology,the problem of laser damage on optical surfaces has become more and more prominent,which has severely restricted the development of high-power laser devices.Generally,the processing of optical components mainly includes grinding,polishing,and reshaping.In these processes,due to the use of abrasive-based processing techniques,physical defects such as tiny brittle/plastic cracks and scratches will be generated on the surface of the component,which will not only affect the mechanical properties of the optical components,but also greatly affect the optical performance of the optical components.At the same time,these defects will also retain chemical pollution such as polishing abrasives,causing laser-induced damage to the optical components in the high-energy/high-power laser system,leading to the failure of the optical components.In high-power optical systems,the absorption coefficient of silicon at 1.2-7?m and 25-300?m wavelengths is less than 10^-7 cm^-1,where the absorbed laser energy is small,and most of the laser energy is transmitted.Therefore,the high-power optical systems has been widely used in power laser devices.In this paper,for mid-infrared optical materials,a multi-physics mid-infrared high-energy laser damage model is established.Starting from different processing technologies and samples from different manufacturers of the same processing technology,the cleaning process,non-destructive testing needle technology,post-processing and damage threshold are studied.The main research results obtained during the master's degree are as follows:(1)We have established a photothermal multiphysics coupling metamaterial absorber model.First,an optical absorber is designed,which is composed of a T-shaped array on the top layer,a silicon dioxide insulator material in the middle layer,and a gold material on the bottom layer.Secondly,three kinds of light and heat absorbers are designed based on the improvement of the optical absorber,which realizes the movement of broadband and the conversion between broadband and multi-wavelength respectively.In addition,the terahertz absorber with dynamic tuning characteristics can flexibly control the absorption performance,providing a good platform for the realization of terahertz filtering and modulation.(2)We have established a mid-infrared high-energy laser damage model coupled with light,heat,and force,which mainly studies the laser-induced thermal damage mechanism on the surface of single crystal silicon mirror irradiated by mid-infrared high-energy laser.We have obtained the transient temperature field and thermal stress field under different conditions by changing the output power density of the laser,the diameter of the laser spot,the radius of the optical element,and the thickness of the optical element in the model.The simulation calculation results show that we can predict the irradiance that initiates cracking and melting by calculating the irradiance at which the calculated thermal stress and temperature exceed the corresponding limits of the fracture strength and melting point,respectively.(3)The direct relationship between surface/subsurface defects and damage of optical components and the post-treatment of defects are studied.In the aspect of simulation,the optical component damage model with defects is established through the multi-physics model of light,heat and force,and the damage under different types of defects is studied.In the aspect of experiment,the cross-scale detection and characterization of mid-infrared high-energy laser components are studied.The surface shape and defects of the substrate were detected by the fluorescence scattering imaging system,and the images of the surface and subsurface were obtained;The reflection photothermal weak absorption detection technology is used to detect the absorption of the substrate surface of the mirror,and the weak absorption value of the substrate surface of the mirror is obtained to judge the distribution of defects and impurity elements;The white light interferometer is used to detect the surface scratches and pits of the mirror,and the three-dimensional imaging and size of the surface scratches and pits are obtained;To F-SIMS test technology is used to detect the impurity metal elements in the sub surface of the mirror,and the type and proportion of the sub surface impurity distribution are obtained.(4)The anti-damage ability of mid-infrared optical components is studied.Firstly,we established a test method for continuous laser damage threshold.Secondly,we built a mid-infrared continuous laser damage test system.Through the damage test of different processing technology and different processing methods of optical components,the influence of different processing technologies and post-processing methods on the damage threshold is studied,combined with the detection and characterization data of the optical component nano-damage precursor in Chapter 3,to find out the defects the relationship with injury.