Influence Of Reparied Morphology In Fused Silica On Transmission And Modulation Of 3ω Laser

Fused silica components are widely applied in many optics, the damage on their surface must be valued. Once, the damage is produced on fused silica surface which causes a reduction in laser induced damage threshold of the component and damage downstream components. The surface damage is repaired by CO₂ laser in engineering, but repair morphology will impact on the transmission and modulation of laser. So, how to optimize placement morphology and repair components and raw materials is essential. In this paper, the research object are large size repair morphologies by the two commonly used CO₂ laser repair techniques, that are Gaussian type crater of non-evaporative repair and cone type crater of evaporative repair. The numerical simulation is used for researching the repair morphologies on laser modulation rules, and provides a reference for repair technology. Specific content as follows:1. Based on the scalar diffraction theory, combining with MATLAB software, two different repair morphologies on fused silica surface are abstracted away as mathematical model. Using Fresnel diffraction integral, the models are bound to the physical process of diffraction. According to the different repair morphologies, the transmission phase modulation process of three times double frequency laser is simulation studied.2. For the Gaussian repair morphology, the relationship between the modulation（distortion of diffraction intensity） and the repair crater vertical depth, horizontal radius and downstream component placement is calculated. The results show that, with the increases of repair crater depth, the modulation distribution was "sawtooth" and get the maxima in different location; when the radius is smaller than 300μm, radius have little effect for modulation, the modulation quickly increases while the radius is greater than 300μm; For the repair morphologies of different size and the aspect ratio（depth/radius） fixed, the maximum of diffraction field appear in 2cm of repair components downstream, when the radius is 450μm, the values of modulation up to 4.7. The calculation results are consistent with the experimental results. Therefore, in the project, the laser modulation change over distance can be predicted through the type and size of actual repair morphology, guide the downstream components placed in the right location.3. For the cone repair morphology, the research methods similar to the Gaussian. The relationship between modulation and depth, radius and downstream component placement is calculated. The results show that, the modulation peak can be affected by depth and radius of the morphology, the narrow and deep repair crater modulate laser field strongly, the modulation of wide and shallow repair crater is relatively small; the modulation of radius 450-650μm repair crater is strong; Compared with the Gaussian repair morphology, the modulation peaks of cone crater close to the rear surface of repair components, and with the increases with distance, the modulation is small and little fluctuation. The calculation results are agree with the experimental results.In this paper, the modulation process of incident light is simulated by MATLAB. The results show that, Evaporative morphology technology is more conducive to the improvement of laser transmission phase distortion, the calculated results for the improvement of CO₂ laser repair technology and the placement of downstream components in laser optical can provide references.