使用多光谱手段研究熔石英断裂机理

熔石英玻璃是高能激光系统中不可缺少的光学材料,其损伤问题一直是限制系统能量提升的瓶颈之一。通过纳秒激光脉冲诱导熔石英玻璃样品产生断裂,并使用多光谱手段对断裂前后样品进行检测,从而在实验和理论上了解了样品断裂形貌及内部相变结构成因,并从宏观到微观上统一解释了断裂形貌和相变结构的关系。在激光等离子冲击波作用下,熔石英发生断裂,且冲击波作用过程中在玻璃内部产生了推动裂纹扩展的尖端环向应力。在尖端环向应力作用下,不同损伤区域形成了不同扩展速度和长度的裂纹,按照裂纹形貌特性差异可以将断裂区分为雾化区、羽毛区、镜面区三个部分。使用透射光谱、能量散射光谱检测损伤前后样品,发现裂纹的产生引起了玻璃透过率和带隙的下降,且断裂区出现氧原子游离或缺失;使用Raman光谱检测样品损伤前后不同形貌区,发现等离子冲击波使熔石英中Si—O—Si键断裂并发生重组,导致镜面区、羽毛区、雾化区三元拓扑环和四元拓扑环宏观上对应的斯石英相和柯石英相的相对含量依次升高,破坏了材料的固有原子结构特性,使材料断裂区向高密度相转变。氧游离的发生会在玻璃内部产生的大量缺陷,从而使得玻璃透过率及带隙下降,严重影响了玻璃的性能。

Study on the Fracture Mechanism by Multi-Spectrum Methods

Fused silica glass is a kind of indispensable material in high-energy laser system,and the damage of it has been one of the bottlenecks restricting the energy of system.In this paper,laser pulse shock wave was used to break down the fused glass samples,then the cause of the morphology of fractures on fused silica glass surface as well as internal phase transition were investigated experimentally and theoretically by multi-spectrum detecting of the samples before and after fracture,and the rela-tionship between fracture morphologies and phase transition structure was explained from macro to micro.The fracture of the fused silica was induced by laser plasma shock wave,and during the shock wave,the tip of hoop stress produced from the inside glass would promote the crack propagation outward.We found that the whole fracture region could be divided into hackle zone, mist zone and mirror zone by morphology differences produced by the tip of hoop stress.The transmittance spectra and energy dispersive spectrometer were used to detect the samples before and after fracture.The results showed that the decrease of the transmittance and band gap of the glass were induced by the cracks,and the oxygen free or absent appeared in the fracture zone. Using the Raman spectrum to detect the different morphological areas of samples before and after broken,we found that the Si—O—Si band of fused glass breakage and recombination could reduce the relative content of three- and four-number rings structures corresponding to the stishovite and coesite of hackle zone,mist zone and mirror zone at the macro level.This kind of changes destroyed the mesh topology severely and induced the material fracture zone transforming to a higher density phase. From the micro level,the non-bridging oxygen hole center and E'center led to the decrease of the optical band gaps as well as transmittance which seriously affected the performance of glass.