Fused Silica Glass: Laser-induced Damage on Bending Strength Weakening and Safety Design

doi:10.15541/jim20220610

Abstract

Abstract:

Laser-induced damage is the fundamental cause of sudden rupture of fused silica vacuum optical elements. To investigate this damage on bending strength weakening to find safety design method, standard samples were made with fused silica vacuum optical elements in the final optics assembly of the SG-III prototype laser facility. The surface damage morphological characteristics of fused silica glass samples were statistically analyzed, and the influence of laser-induced damage on bending strength of fused silica glass samples was investigated. The results show that the damage morphology of laser-induced fused silica glass is typically semi-ellipsoid, the depth of the damage point increases with its length which is no more than 2 mm; The damage point has obvious influence on the bending strength of fused silica glass, whose average bending strength with damage point is only 0.41 times that of the samples without damage point. With increase of the length and depth of the damage point, the bending strength of the samples generally decrease. But when the length of the damage point exceeding 15 mm, its bending strength downward trend is significantly moderated, the ratio of length to depth of the damage point has no obvious effect on the bending strength. These data suggest that designing safe optical elements of fused silica glass vacuum window should comprehensively take into account dispersion of glass bending strength, persistent effect of the stress, and the maximum bending tensile stress distributed near the damage point should not exceed the design value of bending strength.

Key words: vacuum window optical element, fused silica glass, laser-induced damage, bending strength, safety design

CLC Number:

TQ174

JIN Sai, LIU Xiaogen, QI Shuang, ZHAO Runchang, LI Zhijun. Fused Silica Glass: Laser-induced Damage on Bending Strength Weakening and Safety Design[J]. Journal of Inorganic Materials, 2023, 38(6): 671-677.

Figures/Tables 12

Fig. 1 Photo of optical elements with damage points in the fused silica glass vacuum window

Fig. 2 Diagram and physical picture of the sample

Fig. 3 Diagram of the damage point in a sample

Fig. 4 Measurement of morphology and size of damage point (a) Maximum size (2a); (b) Maximum depth (c)

Fig. 5 Damage length (2a) and depth (c) of the damage points in various samples

Fig. 6 Test results of average bending strength of the samples with and without damage point

Fig. 7 Relationship between damage point length and bending strength of the samples

Fig. 8 Fitting curve between damage point length and bending strength of the samples

Table 1 Inversion values of bending strength of fused silica glass corresponding to different damage point sizes

Length/mm	Bending strength/MPa	Length/mm	Bending strength/MPa
0	75.9	21	26.05
1	39.86	22	25.88
2	36.18	23	25.72
3	34.19	24	25.57
4	32.84	25	25.42
5	31.83	26	25.28
6	31.03	27	25.15
7	30.37	28	25.02
8	29.81	29	24.90
9	29.32	30	24.78
10	28.89	31	24.67
11	28.51	32	24.56
12	28.17	33	24.45
13	27.85	34	24.35
14	27.57	35	24.25
15	27.30	36	24.16
16	27.06	37	24.07
17	26.83	38	23.98
18	26.62	39	23.89
19	26.42	40	23.81
20	26.23	-	-

Fig. 9 Relationship between damage point depth and bending strength of the samples

Fig. 10 Relationship between 2a/c values of the damage point and bending strength of the samples

Table 2 K2 and K values of the fused silica glass under various load action time

Load action time	K₁	K₂	K
≤1 min	2.5	1.00	2.50
1 d	2.5	1.85	4.63
30 d	2.5	2.27	5.68
180 d	2.5	2.50	6.25
1 a	2.5	2.63	6.58
3 a	2.5	2.78	6.95
5 a	2.5	2.94	7.35

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