Damage And Stimulated Brillouin Scattering Of Fused Silica By Multi Wavelength Laser Irradiated

With the development of laser technology,the damage of optical elements has become a key problem to restricting the development of large laser facilities.Fused silica is widely used in large laser facilities due to its good optical performance.Irradiated by intense laser,defect induced damage and nonlinear effect are the main reasons for the damage of fused silica optical elements.Defect induced damage refers to absorption and intensity modulation of laser energy due to impurity defects with the irradiation of intense laser.It damage the structure of element;Nonlinear damage is the damage of material structure due to the change of mechanical and optical properties caused by nonlinear polarization.In the terminal optical components of a large laser facilities,components are exposed to multiple wavelengths irradiated at the same time.The damage rules are different from those of single wavelength irradiation.It is important to study the damage of fused silica under multi wavelength radiation.With the development of laser technology,Increasing the output energy of laser.The influence of nonlinear effects on beam propagation and component damage is gradually being emphasized.Stimulated Brillouin scattering is one sort of the nonlinear effects.The high reflection efficiency and strong ultrasonic field of stimulated Brillouin scattering will cause direct damage to the components.And stimulated Brillouin scattering has the characteristics of phase conjugation,time delay and pulse width compression.It has a wide range of applications in the optical system.So Stimulated Brillouin scattering is of great importance.In this paper,the damage of fused silica under multi wavelength irradiation and Stimulated Brillouin scattering in fused silica under different wavelength laser irradiation is studied by experimental method.The main contents are as follows:The damage rule of fused silica optical elements irradiated at different wavelengths and irradiated by two wavelengths simultaneously is studied.The damage probability curve and typical damage morphology are obtained.The results of the study show that,damage threshold of short wavelength laser is lower and damage probability curve rises faster by Single wavelength irradiation;Increase of damage density simultaneous irradiation of two wavelengths.With the addition of quantitative 532 nm laser and 355 nm laser in the 1064 nm laser,the 1064 nm laser damage probability curve will increase faster.532 nm laser and 355 nm laser added quantitative 1064 nm laser,and 532 nm and 355 nm laser damage probability curves did not change significantly.Longitudinal stimulated Brillouin cattering(LSBS)in fused silica optical elements irradiated by different wavelengths is studied.The relation between incident laser energy density and scattering efficiency is studied.The influence of sample length,lens focal length and longitudinal mode of incident laser on the threshold and reflection efficiency of LSBS is studied.The variation of scattering pulse waveform with energy density is observed.The experimental results show that there is a significant threshold effect and saturation effect in the longitudinal stimulated Brillouin scattering.When the incident laser energy density reaches the threshold,the scattering efficiency increases rapidly with the incident laser energy density,but the scattering efficiency remains unchanged after increasing to a certain degree.