Study Of Thermal Deformation Mechanisms Of HR Mirror Irradiated By 1080 Nm High Power CW Laser

The fiber laser with wavelength of 1080nm as one of the mainstream light sources of high power CW laser is widely used in communication sensing,laser processing,military and national defense and other important fields.In these fields,high power CW laser systems are required to have good output performance and beam quality.The high-reflective mirror plays an important role in the control of beam transmission direction in high power CW laser system.As an indispensable component in high power CW laser system,the high-reflective mirror is used to control the beam transmission direction.Due to the continuous laser irradiation for a long time,the high-reflective mirror surface film absorbs the laser energy,which causes the internal temperature of the mirror to produce uneven temperature rise.The uneven temperature rise of the mirror results in the surface deformation of the high-reflective mirror,the quality of the laser beam decreases after the laser is transmitted through the thermal deformed of high-reflective mirror,which makes the laser transmitting system less effective or even invalid to the target.Therefore,it is of great significance to study the thermal deformation of the mirror irradiated by 1080 nm CW laser,this research will help improve the performance of laser emission systems.（1）According to the technical requirements related to the thermal deformation experiments of 1080 nm CW laser irradiation mirror,1080 nm laser high-reflective mirrors were designed and prepared by using Ta₂O₅and Si O₂as high and low refractive index thin film materials deposition on a fused silica substrate.The spectral performance of the high-reflective mirror was analyzed and obtained with the period of the film system of the film layer.By comparing the test spectra with the simulated spectra,it was confirmed that the reflectance of the prepared high reflectance mirror samples at 1080nm met the technical requirements of the irradiation experiment.（2）Based on the heat conduction equation and thermoelastic equation and other related theories,the physical model of the thermal deformation of the mirror irradiated by the high power continuous laser at 1080 nm was established as the geometric model of the prepared mirror.The effects of laser parameters such as output power,spot radius and incident angle on the surface temperature and surface deformation of the reflector were investigated,and the time evolution of the surface temperature and surface deformation of the reflector were analyzed.The influence of the thermal deformation of the reflector surface on the quality of the incident laser beam was analyzed by Zernike polynomial fitting coefficients.（3）An experimental platform for thermal deformation of mirrors irradiated by1080 nm CW laser was built,and the thermal deformation of mirrors irradiated by continuous laser was investigated by using the prepared mirror samples,and the temperature change at the center of the mirror and the change of the surface shape of the mirror were measured online during the irradiation process.The thermal deformation of the reflector during the irradiation process is measured online.The parameters related to laser work in the experiment are simulated,and the simulation results are compared with the experimental results to verify the rationality of the thermodynamic model of the interaction between the 1080 nm continuous laser and the reflector.