The Research On The Damage Mechanism Of Fluorophosphate Glass Induced By High Energy Irradiation

Nowadays,the UV laser induced damage of fused silica optics and the deficiency of present color separation technique have become the key limiting factors restricting the high flux output and stable operation of the laser drive inertial confinement fusion system.The development of novel color separation optics with higher UV laser induced damage threshold for color separation principle innovation will open up new paths to solve the above problem.The series of fluoride-containing phosphate-based glasses with the weight composition of Li₂O?0.5-2?,K₂O?3-5?,MgO?3-5?,BaO?7-10?,Al₂O₃?8-11?,P₂O₅?59-64?,YF₃?0-1?,LaF₃?0-2?developed by our research group have high UV laser induced damage.However,the existing optical damage theory of optical materials can't explain the high damage threshold characteristics and the high energy pulsed laser induced fluorescence emission of the series materials.According to previous works,it was found that the high damage threshold and fluorescence emission of this series of materials are related to the special network structure of the glass.Therefore,this work studies the variation of structural defects in glass by controlling the glass melting atmosphere and introducing B₂O₃ and Si,respectively,which have significant influence on the optical properties of the materials.Meanwhile,?-ray irradiation was used to study the evolution mechanism of structural defects in the fluoride-containing phosphate-based glasses.Besides,the high-energy pulsed laser was employed to reveal the high damage threshold characteristics,and establishes the laser-induced damage theory of the fluoride-containing phosphate-based glasses.The evolutionary mechanism model of structural defects in the fluoride-containing phosphate-based glasses was established to reveal the changes of structural defects in the materials during the glass melting,gamma irradiation and post-heat treatment process.The results show that the reducing glass melting conditions can effectively reduce the concentration of POHC and PO₃-EC structural defects in the fluoride-containing phosphate-based glasses and improve the transmittance of the material in the ultraviolet region.Besides,?-ray irradiation can induce the formation of structural defects such as POHC,OHC,FD,PO₄-EC,PO₃-EC and PO₂-EC in the material,causing the red shift of the ultraviolet absorption cut-off of the material and the decrease of transmittance.Subsequent heat treatment can,to a certain extent,be able to bleach the POHC and OHC defect centers induced by gamma irradiation by charge transfer process.At the same time,the tendency of Co²⁺and(Co²⁺)⁺defects to evolve into FD defects is increased.In addition,two dynamic equilibrium mechanisms of FD defect centers,i.e.POHC?FD and PO₂-EC?FD,were proposed for the first time at heat treatment temperatures of 190°C and 390°C,respectively.The introduction of B₂O₃ and Si in glass materials has a significant effect on the optical properties of the fluoride-containing phosphate-based glasses.The introduction of B₂O₃ reduces the connectivity of phosphate chains and thus increases the concentration of PO₃-EC and PO₄-EC defects in the phosphate glass network that have large absorption in the high-energy region.However,the addition of B₂O₃could enhance the gamma radiation resistance of the phosphate glasses,in this case B₂O₃,and enter the phosphate glass network in the form of B₅O₈ units.The units enhanced the connectivity of the long phosphate chains,and thus reduced the concentration of PO₃-EC and POHC defects in the fluoride-containing phosphate-based glasses.Obvious healing behavior of gamma radiation induced defects in this materials was observed at room temperature.The synchronous decreases of PO₃-EC and POHC defects contribute to the corresponding recovery of the transmittance change at 385 nm and 525 nm,which could be described by the charge transfer.Besides,a general model of the healing mechanism associated with the release and capture of the electrons between PO₃-EC and POHC defects in the materials was proposed.The introduction of a small amount of Si in the fluoride-containing phosphate-based glasses can strengthen the connectivity of the main P chain in the material,reduce the concentration of the PO₃-EC defect in the materials,cause the blue shift of the ultraviolet absorption cutoff edge of the material.When the Si content is further increased,the ultraviolet absorption cutoff edge of the material is further blue-shifted,however,this change does not significantly affect the laser induced zero probability damage threshold of the material.Compared to the 355 nm high-energy laser,the 1064 nm high-energy laser has a higher zero-probability damage threshold when irradiating the fluoride-containing phosphate-based glasses,indicating that the lower the photon energy,the lower the multiphoton efficiency of the material,resulting in the higher laser induced damage threshold.Meanwhile,the higher the-ray pre-irradiation dose,the lower the damage threshold of the material,which indicates that the higher the concentration of POHC structural defects in the material,the lower the damage threshold of the material.Based on the above results,we constructed a damage mechanism model of laser-induced the fluoride-containing phosphate-based glasses to reveal the high damage threshold characteristics of the materials.The laser induced damage of this series materials is mainly due to the multiphoton absorption process.Laser irradiation can induce the generation of initial electrons in the material,which can be accumulated by the multiphoton absorption process,gradually forming a plasma,and the plasma continues to absorb energy,and the accumulation of energy to a certain extent causes ablation and cracking of the material.The laser induced damage threshold of the material is determined by the optical band gap and the content of the POHC structure defect in the material.The narrower the optical band gap in the material and the higher the concentration of POHC structure defects,the higher the multiphoton efficiency during laser irradiation,the more susceptible the material is to damage,and the lower the damage threshold.The research in this work shows that by controlling the glass melting conditions and adjusting the content of B₂O₃ and Si in the glass formulation,the transmittance of the material in the ultraviolet region can be effectively improved,and the concentration of POHC structural defects in the material can be reduced.Which is expected to further increase the laser induced damage threshold of the material and promote the engineering application of the series of the fluoride-containing phosphate-based glasses.