| As a good optical material,fused quartz is widely used in various optical systems.In the long pulse output optical system with specific wavelength,in order to obtain better beam output quality,it is often necessary to coating on the surface of fused quartz material.When the surface of the material is damaged,the beam output quality will inevitably be affected.Therefore,it is of great significance to study the surface damage of fused quartz induced by long pulse laser.At the same time of the surface damage,there will be the phenomenon of laser-induced plasma,which absorbs the laser energy through the mechanism of reverse toughening absorption,and then forms a laser-supported combustion wave.When the lasersupported combustion wave is generated,it will go through some physical processes,such as temperature rise,material phase transition,surface damage,plasma absorbing laser energy to produce combustion wave and so on.In this paper,the physical process of plasma generation and combustion wave expansion of fused quartz induced by millisecond pulse laser is systematically discussed from three aspects: theoretical research,simulation research and experimental research.At last,the dynamic propagation mechanism of plasma and combustion wave produced by millisecond pulsed laser induced antireflection fused quartz is clarified.In the aspect of theoretical research,the physical process of plasma and combustion wave produced by millisecond pulsed laser induced fused quartz is theoretically analyzed based on the theory of hydrodynamics and plasma theory.In the model of laser supported combustion wave,the effects of different energy on the evolution of target steam,plasma and combustion wave are considered.The initial and boundary conditions are modified according to the characteristics of laser combustion wave produced by fused quartz irradiated by millisecond pulsed laser.In the aspect of simulation research,a simulation model of the temperature field and velocity field of the plasma generated by millisecond pulsed laser induced fused silica is established,and the results of the temperature field and velocity field are mainly analyzed.In study of temperature field,the law of surface temperature change of radial materials with time is mainly analyzed,and in terms of velocity field,the kinetic behavior of plasma and combustion waves induced by millisecond pulse laser induction is mainly analyzed from the time and space dimensions,and the change of combustion wave velocity with time and temperature under different laser energy is analyzed.The simulation results show that the peak velocity of plasma and combustion wave is positively correlated with temperature within a certain laser energy range.In terms of experimental research,by controlling the positional relationship between the focus and the target,the experiment can be divided into three groups,they are: the target is in front of the focus,the front surface of the target is in the focus,and the target is behind the focus.The change process of surface temperature of fused quartz irradiated by millisecond pulse laser with time under different laser energy was measured and analyzed.It was found that the laser and surface temperature lost coupling phenomenon.The damage morphology of fused quartz was measured by metallographic microscope.It was found that the boundary between the damaged area and the undamaged area before the focus and after the focus was obvious,and a large area of heat affected zone appeared in the focus group.The evolution images of laser-induced plasma and combustion waves are captured by a high-speed camera and the above processes are analyzed.Through the analysis of the optical shadow image and combined with the simulation results,the dynamic behavior and the mechanism of generation and propagation of plasma and combustion wave induced by millisecond pulse laser are clarified. |
