High temperature thermal behaviour modeling of large-scale fused silica optics for laser facility

Abstract

High temperature annealing is often used for the stress control of optical materials. However, weight and viscosity at high temperature may destroy the surface morphology, especially for the large-scale, thin and heavy optics used for large laser facilities. It is necessary to understand the thermal behaviour and design proper support systems for large-scale optics at high temperature. In this work, three support systems for fused silica optics are designed and simulated with the finite element method. After the analysis of the thermal behaviours of different support systems, some advantages and disadvantages can be revealed. The results show that the support with the optical surface vertical is optimal because both pollution and deformation of optics could be well controlled during annealing at high temperature. Annealing process of the optics irradiated by CO2 laser is also simulated. It can be concluded that high temperature annealing can effectively reduce the residual stress. However, the effects of annealing on surface morphology of the optics are complex. Annealing creep is closely related to the residual stress and strain distribution. In the region with large residual stress, the creep is too large and probably increases the deformation gradient which may affect the laser beam propagation.

Laser-Induced Damage Initiation and Growth of Optical Materials

“…This process can be simulated by a finite-element method. We considered bulk fused silica with a surface heat source due to the small absorption depth of CO 2 laser radiation [52]. The temperature evolution and residual stress distribution are estimated, which are consistent with experiments.…”

“…For the long pulse or continuous wave, ionization hardly occurs while thermal absorption is the dominant process. Temperature evolution, residual stress and strain, and melting morphology (if the laser intensity is high enough) can be estimated using heat conduction model [52].…”

Optimization of fixture layouts of glass laser optics using multiple kernel regression

“…In their paper, the model was finally validated using FEA. Yu et al [16] analyzed the thermal behaviors of three different support systems, which they called multi-points support, four edge support, and side face support, for fused silica optics with the finite element method, so that a suitable support scheme to reduce the residual stress was designed based on the analysis. Ning et al [17] built a finite element model to analyze the influence of thickness, thermal expansion coefficient, and Young's modulus of materials on thermal stability.…”

ATR-FTIR spectroscopic studies on density changes of fused silica induced by localized CO 2 laser treatment

“…[8,15,16] However, some problems, such as raised rims, re-deposited debris, bubbles or residual stress at the mitigated damage sites, may occur when using the non-evaporative mitigation protocol and they will lead to problematic damage re-initiation and growth, as well as downstream intensification. Extensive investigations have been conducted to solve these problems, [4,8,[15][16][17][18][19][20][21][22][23][24] and the non-evaporative mitigation protocol with the combination of particular powers and exposure times of CO 2 laser can effectively eliminate raised rims, re-deposited debris, and bubbles at the mitigated damage sites. [8,[15][16][17][18][19][20][21][22] In addition, high temperature oven annealing or laser annealing can effectively control the residual stress to an acceptable level.…”

“…[8,[15][16][17][18][19][20][21][22] In addition, high temperature oven annealing or laser annealing can effectively control the residual stress to an acceptable level. [21][22][23][24] These modifications of the mitigated damage sites induced by intensive CO 2 laser treatment are associated with the local structural changes of fused silica. However, few studies on the structural changes of fused silica treated with localized CO 2 laser heating have been reported.…”