Two localized CO ₂ laser treatment methods for mitigation of UV damage growth in fused silica

Abstract

Two methods: high-power, short-time, single-shot irradiation (Method A) and low-power, long-time, multi-shot irradiation (Method B) are investigated to mitigate the UV damage growth in fused silica by using a 10.6-μm CO2 laser. To verify the mitigation effect of the two methods, the laser induced damage thresholds (LIDTs) of the mitigated sites are tested with a 355-nm, 6.4-ns Nd:YAG laser, and the light modulation of the mitigation sites are tested with a 351-nm continuous Nd:YLF laser. The mitigated damaged sites treated with the two methods have almost the same LIDTs, which can recover to the level of pristine material. Compared with Method A, Method B produces mitigated sites with low crater depth and weak light modulation. In addition, there is no raised rim or re-deposited debris formed around the crater edge for Method B. Theoretical calculation is utilized to evaluate the central temperature of the CO2 laser beam irradiated zone and the radius of the crater. It is indicated that the calculated results are consistent with the experimental results.

Effect of annealing on the laser induced damage of polished and CO2 laser-processed fused silica surfaces

“…Strategies and techniques have been developed to prevent the extend of the damage sites under successive irradiations. [5][6][7][8][9][10][11][12][13][14][15] Local CO 2 laser processing in air atmosphere is the main technique used to mitigate laser damage sites on fused silica optics. It is used in volume production on the National Ignition Facility to "repair" the damage sites and recycle the optics, 16 and should be deployed to operate the LaserMegaJoule.…”

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.…”

“…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. [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.…”

“…[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.…”

Investigation of Control of Residual Stress Induced by CO2Laser-Based Damage Mitigation of Fused Silica Optics

“…Therefore, an effective control of the residual stress to an acceptable level is necessary for the mitigation of larger damaged sites by the nonevaporative approach. Jiang et al reported that the nonevaporative technique can be used to mitigate damaged sites with lateral sizes as large as 400 m, but the high temperature annealing by using an oven must be applied to relieve the residual stress of the mitigated sites [11,12]. In this paper, the nonevaporative approach is explored to mitigate the damaged sites as large as 250 m, and the investigation of the CO 2 laser-based annealing technique is conducted to suppress the residual stress left on the surface of fused silica optics for the mitigation of larger damaged sites by the nonevaporative approach.…”