Study On Thermal Effect And Damage Properites Of Quartz Fiber Based On Finite Element Method

Quartz fiber,as a kind of common energy transfer fiber,is easy to be damaged under the condition of high-energy laser irradiation,thus the transmission efficiency of the whole optical system is affected.In the mechanism of laser-induced fiber damage,the damage caused by the thermal effect of fiber is easy to affect the fiber system.At present,there are few studies on the thermal effect and damage properties of quartz fiber by using finite element method.In this paper,the thermal damage caused by kilowatt level laser in high purity quartz fiber model is studied by using finite element method.The optical fiber loss,thermal absorption and melting damage are studied by simulation.The thermal damage induced by high energy laser is studied in a high purity quartz fiber model by finite element method.Wave optics,ray optics,solid-state heating and beam envelope method are used to simulate the thermal effect of kW laser in quartz fiber.The variation of surface temperature with time and the distribution of internal thermal field are analyzed by simulation.The main contents of this paper are as follows:(1)The finite element model of laser incident fiber is constructed.The coupling structure of the short focal lens focused laser incident into the fiber is restored.The wavelength of 1064 nm kW laser is used as the incident light source,and the focal spot radius of the incident light source is obtained by ray tracing;(2)Thermal analysis of the effect of high energy laser on fiber surface.The loss caused by laser incident into the fiber is calculated by wave optics method,which is equivalent to the heat source power at the input end of quartz fiber.The surface temperature,internal temperature distribution and the maximum surface temperature with time of quartz fiber are obtained by solid heating method.(3)The influence of thermal field distribution on the nonlinear effect of optical fiber.The influence of thermal field on nonlinear effect of quartz fiber is analyzed by beam envelope method.The distribution of electric field mode and refractive index in quartz fiber is calculated,and the result of energy transfer efficiency reduction is obtained.The refractive index changes of high purity silica fiber with or without thermal field distribution are compared and analyzed.The results show that if there is no proper thermal management,the 1064 nm laser injection of more than 1000 W will cause melting damage to the surface of high purity quartz fiber.The existence of thermal field distribution will aggravate the nonlinear effect of quartz fiber and affect the energy transfer efficiency.This research has a theoretical guiding role for the research of fiber damage caused by laser.