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Micro surface defects (SDs) would be unavoidably induced on most fused silica surfaces (FSSs), substantially reducing their laser-induced damage thresholds (LIDTs). There is still no clear understanding of the relation between SD structural feature and their LIDTs, which poses a challenge to the recognition and mitigation of the dangerous SDs with low LIDTs in industrial production. In this work, the brittle-plasticity and stress states of the SDs are found to dominate the atomic point-defect densities on FSSs and resultantly dominate their LIDTs for the first time. Based on this, the SDs have been divided into four categories: pressure-induced brittle defects (PBDs), pressure-induced plastic defects (PPDs), tension-induced brittle defects (TBDs) and tension-induced plastic defects (TPDs). Based on the tested LIDTs, laser damage morphologies and photoluminescence (PL) characteristics, the laser damage resistance of different kinds of SDs are compared, whose reasons are revealed on the basis of the molecular dynamics (MD) simulations. The sharp increase of the atomic point-defect density from the plasticity to the brittleness of the material, the significant disparity in tensile and compressive strength of fused silica, the distinctly different material response behaviours under tensile and compressive forces, as well as the opposite effects of the tensile and compressive forces on the material compactness significantly affect the atomic point-defect densities on FSSs and resultantly contribute to the different laser damage resistance of different kinds of SDs. This work possesses great significance in solving the laser damage on FSSs. It could also provide a new understanding of the impact of the tensile and compressive forces on the LIDTs of various optical elements. [ABSTRACT FROM AUTHOR]

[Display omitted] • There are amounts of point defects at the atomic scale in the residual stress zones. • The STE point defects at the atomic scale distributed on the fused silica surface are found to be closely related to the residual stress on the fused silica surface for the first time. • PL-detection method is proposed to characterize the residual stress on the material surface for the first time. • The relative amount of STE point defect (K = S / S 0) is first proposed to quantitatively characterize the residual stress. The residual stress would have a significant impact on the service performance and fatigue life of the fused silica (non-crystal material) components (e.g., Hemispherical Shell Resonator). However, there is still no effective method for characterizing the residual stress on their working surfaces. Therefore, it is essential to develop a novel method for characterizing the residual stress on fused silica surfaces. Herein, the residual stress is found to significantly affect the mechanical properties of fused silica surfaces. On the basis of the study on the photoluminescence (PL) properties of residual stress zones, atomic point defects are found to be closely related to the residual stress. Based on an investigation of the PL properties of different types of mechanically processed surfaces, four types of point defects (ODCII, STE, Si clusters and NBOHCI) have been determined. On the basis of the molecular dynamics (MD) simulation results and the PL experiments on different types of mechanically processed surfaces, STE point defects at the atomic scale are found to be closely related to the residual stress for the first time. Based on this, PL-detection method is proposed to characterize the residual stress on the material surface for the first time. Besides, the relative amount of STE point defect (K = S/S 0) is first proposed to quantitatively characterize the residual stress. In sum, this work determines the structure at the atomic scale which is closely related to the residual stress and opens a convenient door to quantitatively characterize the residual stress with PL-detection method. It could also provide a reference for the characterization and even the alleviation of the residual stress on the surfaces of other non-crystal materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • A reciprocal relationship between the highest photoluminescence intensity (HPI) and the laser-induced damage threshold (LIDT) of the surface-defect zone is constructed for the first time. • The physical mechanism of the sharp decrease of the LIDT from plastic to brittle surface defects is revealed for the first time. • The slight increase of the HPI would lead to a sharp decrease of the LIDT from plastic to brittle surface defects. • E'-Center and STE point defects would increase sharply from plastic to brittle surface defects, causing a sharp increase of HPI. Micro-nano surface defects are inevitably introduced on mechanically processed fused silica surfaces and even almost all the optical glasses, severely decreasing their laser-induced damage thresholds (LIDTs). There are two types of defects: brittle surface defects and plastic surface defects, whose diverse structural characteristics could affect their influence on the LIDTs. Due to their tiny dimensions, brittle and plastic defects are difficult to be distinguished and identified clearly in industrial production. However, there is a sharp decrease (even to 10%) of LIDT from plastic to brittle surface defect, whose mechanisms have not been revealed. Herein, a reciprocal relationship between the highest photoluminescence intensity (HPI) and LIDT of the surface-defect zone is constructed for the first time. The increase of HPI is found to cause a sharp decrease of the LIDT when HPI is low, which is the first cause of the sharp decrease of LIDT. E'-Center and STE point defects would substantially increase from plastic to brittle surface defect, causing a sharp increase of HPI, which is the second cause. This work fundamentally reveals the mechanisms of the sharp decrease of the LIDT from plastic to brittle surface defect, which is beneficial to characterize and mitigate the hazardous brittle surface defects. [ABSTRACT FROM AUTHOR]