Optical modulation of repaired damage site on fused silica produced by CO₂ laser rapid ablation mitigation*

Abstract

CO2 laser rapid ablation mitigation (RAM) of fused silica has been used in high-power laser systems owing to its advantages of high efficiency, and ease of implementing batch and automated repairing. In order to study the effect of repaired morphology of RAM on laser modulation and to improve laser damage threshold of optics, an finite element method (FEM) mathematical model of 351 nm laser irradiating fused silica optics is developed based on Maxwell electromagnetic field equations, to explore the 3D near-field light intensity distribution inside optics with repaired site on its surface. The influences of the cone angle and the size of the repaired site on incident laser modulation are studied as well. The results have shown that for the repaired site with a cone angle of 73.3°, the light intensity distribution has obvious three-dimensional characteristics. The relative light intensity on z-section has a circularly distribution, and the radius of the annular intensification zone increases with the decrease of z. While the distribution of maximum relative light intensity on y-section is parabolical with the increase of y. As the cone angle of the repaired site decreases, the effect of the repaired surface on light modulation becomes stronger, leading to a weak resistance to laser damage. Moreover, the large size repaired site would also reduce the laser damage threshold. Therefore, a repaired site with a larger cone angle and smaller size is preferred in practical CO2 laser repairing of surface damage. This work will provide theoretical guidance for the design of repaired surface topography, as well as the improvement of RAM process.

Etching behavior of ground fused silica and light enhancement modulated by surface/subsurface cracks

“…E max is significantly increased to be ∼1.60 V/m when the subsurface cracks are completely opened as craters at the etched depth of ∼4.37 µm, meanwhile, further etching with 9.77/13.97 µm away enlarges the aperture size of craters simultaneously relieves the E max to be ∼1.43 and ∼1.46 V/m, respectively. There is a quadratic relation between the intensity of light field I and electric field E in a single medium (such as fused silica), as following formula shows 25 : $$\begin{equation}I\; = \frac{1}{2}\;\sqrt {\frac{\varepsilon }{\mu }} {\left| E \right|^2}\end{equation}$$…”

Model predictive inverse method for recovering boundary conditions of two-dimensional ablation*

“…Measurement of time-and space-dependent heat flux is widely carried out in numerous engineering applications, such as aerospace industry, [1][2][3][4] metallurgy industry, [5,6] combustion diagnosis, [7,8] and biomedical engineering. [9,10] Direct measurement of transient heat flux is often difficult in many industry fields, such as the heat flux on thermal protection shield surface of the re-entry vehicle, and the cooling heat flux on the casting surface that determines the casting quality of continuous casting process.…”