Open Access
Add to BibSonomy
Abstract
Near-surface nanoscale damage precursor generated from the fabrication process has great influence on laser-induced damage threshold improvement of fused silica. In this work, high-resolution transmission electron microscopy (HRTEM) is used to characterize the arrangement of material particles near surface. The nanoscale defects in the Beilby layer could be clearly distinguished. And we find ion beam etching (IBE) has little effect on the arrangement of material particles. This microscopic phenomenon makes IBE a promising technique for the detection of nanoscale near-surface damage precursors. To further investigate the nanoscale near-surface damage after chemical mechanical polishing, a trench is generated by ion sputtering to contain the nature and characteristics of nanoscale precursors in different depths. The evolutions of chemical structure defects and nanoparticles are measured and their laser-induced absorption performance are tested. The results show that there is a nanoscale defect layer (~360nm) beneath the Beilby layer. A model for nanoscale defect layer of fused silica after CMP is offered. In the model, the quantitative density of nanoparticles falls exponentially with increasing the depth and the contents of ODC and NBOHC decreases linearly, respectively. Research results can be a reference on characterizing nanoscale defects near surface and conducting post-processing technologies to improve the laser damage resistance property of fused silica.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Fused silica optic is of critical importance in the development of high-power laser systems. To improve the laser induced damage threshold (LIDT) of fused silica optics is one of the basic pursuing objectives for high-power laser systems [1–3]. In the fabrication process of fused silica optical components, due to its brittleness removal mechanism, subsurface damage such as scratches are often generated during grinding and/or polishing on the subsurface of optical components, which seriously affect the ability of anti-laser induced damage on the high-performance optics [4–7]. In recent years, this demand on low-damage fabrication has prompted the development of chemical/mechanical polishing (CMP) as a process technology. In CMP, the chemical processing methods can avoid the polishing load and restrain the local densification effect. Then, fused silica without subsurface damage can be obtained [8]. However, because of synergistic chemical and mechanical interactions in CMP, a modified amorphous layer will be formed which ranges in thickness from a few nanometers to a micron. This layer is often referred to as the Beilby layer, the polishing layer, the modified layer, and/or the hydrated layer [9]. What is more, a variety of defects at size scales below that which can be reliably observed by optical or even electron microscopy, when precipitated beneath the Beilby layer, can seriously lead to laser damage. Literatures [10–13] show that two main kinds of nanoscale defects are responsible for igniting laser damage of fused silica. One is highly absorptive contaminants (e.g., Ce, Fe, etc.) and the other is chemical structure defect. These nanoscale damage precursors can decrease light transmission levels, discolor the glass, alter the index of refraction, alter the density, and increase absorption levels of the glass during high power/energy laser irradiation. Laser induced damage always occurs at the surface of fused silica optics which contain a lot of nanoscale defects induced by manufacture. Nanoscale defects beneath surface represent a new significant barrier to the fabrication of UV optics for high fluence applications [14,15]. Therefore, the detection and control technologies for near-surface nanoscale defect layer are of great importance in conducting the post processing technology of damage-free high-performance optics.
To inspect near-surface defects correlated with laser damage precursors at nanoscale before post process technology, many laboratories make efforts in optical defects characterization. One common technique to inspect near-surface contaminations is the inductively coupled plasma atomic emission spectrometer (ICP-AES) which track redeposition layer contaminants with a high sensitivity for trace elements [16]. Another effective technique is Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) [17]. It has a high sensitivity (on the order of magnitude of ppm to ppb for most species) for trace elements or compounds and can analyze surface and depth profiling of insulating and conducting samples. But both ICP-AES and TOF-SIMS cannot characterize the morphology of nanoscale near-surface defects.
Trogolo successfully imaged the Beilby layer of silica glass in cross section using transmission electron microscopy and estimated its depth between 100 and 200 nm [18]. Liao performed similar measurements [19]. However, details of near-surface nanoscale damage precursors beneath the Beilby layer in cross section is still rarely shown. In addition, no direct measurement of chemical structure defects distribution near surface has been reported. Although a few literatures [12,13] have reported advantages of some post process in mitigating chemical structure defects.
To date, it is difficult for the current methods to maintain the original morphology of the subsurface. Accompany with the formations of the subsurface damage or the Beilby layer will seriously influence the detection of nanoscale damage precursors. In previous studies [11,13], ion beam etching (IBE) techniques for improving laser damage resistance were focused on the final effect. Researchers usually focus on the results on getting super-smooth surface or improving LIDT in the IBE. Evidently, it is controllable, highly stable and non-contact with advantages over conventional post-process technology and uses ion sputtering effect to remove material at atomic scale for super-smooth surface. External contamination can be avoided to introduce on the surface in the IBE. As a promising technique for the detection of nanoscale near-surface damages, IBE has a possibility to be applied in removing the Beilby layer and exposing internal nanoscale defects without introducing new defects, which make a good preparation for characterization. Similar, Liao finds that IBE is very sensitive to the local densification, and uses it for the detection of nanoscale subsurface local densification [8].
The purpose of this work is focus on the characteristics and evolution of near-surface nanoscale precursors assisted by IBE. Details in the different depths of polished surface nanoscale damage precursors are shown. Section 2 is about experimental design. The results of defects detection and characterization techniques are described in Section 3. Section 4 is devoted to the analysis and discussions of the obtained results and Section 5 draws the conclusions. Above all, results can be a reference on using IBE process technology to detect nanoscale damage precursors and conducting to fabricate the damage-free surface of fused silica optics for improving laser-induced damage threshold.
2. Sample manufacturing
A fused silica sample (Heraeus 312) with size of 50 × 50 × 5mm3 is prepared by a vendor called LANGUANG Optical Technology CO., LTD. It is polished by CMP, which effectively avoid the densification effect occurs in the material removal process and simultaneously remove the subsurface damage. Then owing to fabrication on the atomic-scale, a trench is polished by IBE on the surface of sample to detect the micro-topography of beneath surface in cross section (Fig. 1). The sample is processed in the KDIBF650L-VT Ion beam etching machine developed by ourselves. The value of IBE parameters are shown in Table 1. The removal rate of material in the IBE is a determined value. When the processing time and processing area are determined, the removed depth is determined as well. In order to study the distribution of nanoscale damage precursors beneath the Beilby layer, the etching depth must be large enough, and contain enough detection steps. Therefore, we finally polish a 250nm trench by IBE and detect the micro-topography of beneath surface at six depths in cross section. The depth of the trench is measured by interferometer and the points to be measured are marked at the different material depth. To characterize the surface morphology at the different material depth, atomic force microscopy (AFM, Bruker Dimension Icon) in ScanAsyst mode is used to investigate the six points. The measurement range of AFM is 5μm × 5μm. In addition, the chemical structure defects at the different material depths are detected by fluorescence spectra analysis, which can provide the fluorescence intensity information of the measured areas.
Table 1. Parameters of IBE
In order to prove the feasibility of above experimental design and more detailed display the beneath surface material quality, a direct test method is used here to investigate the influence of IBE on material surface quality. Cross-sectional high-resolution transmission electron microscopy (Talos F200X, produced by FEI Inc., America) experiments are taken in point (a) and point (f) in trench. Surfaces of these two points are machined by CMP and IBE, respectively. Talos F200X combines outstanding high-resolution S/TEM and TEM imaging with industry-leading energy dispersive x-ray spectroscopy (EDS) signal detection and 3D chemical characterization with compositional mapping. The Talos F200X S/TEM allows for the fastest and most precise EDS analysis in all dimensions, along with the best high resolution TEM imaging with fast navigation for dynamic microscopy.
3. Results
3.1. Transmission electron microscopy analysis
Figure 2(a) shows a cross-sectional sample that is firstly prepared by the focused ion beam (Helios 600i, the dual beam of reference for ultra-high resolution of imaging, high quality sample preparation and nanofabrication, produced by FEI Inc., America) and then the central area of this sample is thinned by an ion milling.
Fig. 2 Cross-sectional HRTEM image showing near surface at 0nm of fused silica: (a) fused silica sample after ion milling; (b) the Beilby layer formed in Zone 1 during CMP; (c) the TEM image of fused silica matrix in Zone 2.
In TEM, imaging contrast formation arises from the interference between center transmitted electron, beam and diffraction beam passing through crystalline materials. The contrast in HRTEM is phase contrast, which is typically shown as lattice fringes. The underlying reason could be ascribed to the amorphous phase material, the detailed atomic structure of fused silica cannot be imaged clearly by the TEM, whereas the nanoscale defect characteristics would be distinguished when the adjacent areas comprised by the materials of different properties. TEM image at the resolution of 20nm in Fig. 2(b) shows that the Beilby layer can be observed even though interface between Beilby layer and the matrix is not distinct enough. The Beilby layer (depth 0-20nm) are full of tiny white bits, and distinguishes from the arrangement of the material particles of the further deeper near surface (depth>20nm) [Fig. 2(c)]. What is more, the distribution of tiny white bits is very uniform near surface as well. It is possible that tiny white bits may be the residual polishing powder in nanoscale and the chemical structure defects of fused silica.
To further analysis the composition of these tiny white bits, energy dispersive x-ray spectroscopy signal detection is carried out. The detection zone is captured in Fig. 2(b). The mapping results of several main elements are displayed in the Fig. 3. Pt and C ions, which come from focused ion beam coating, are distributed above the surface. Ga ions will be implanted into the cross-sectional sample when it is firstly prepared by the focused ion beam. And the distribution of Ga ions is consistent with that of tiny white bits. The EDS mapping results show that there is no other chemical element existing in the near-surface depth layer. These tiny white bits are more likely to be structural defects rather than residual polishing contamination in nanoscale. Owing to the existence of chemical structure defects, more Ga ions will be implanted into the vacancy regions in the arrangement of the material particles, which is characterized as nanoscale tiny white bits in TEM.
Later, in order to verify IBE has little effect on the arrangement of the material particles, another Cross-sectional transmission electron microscopy experiment is carried out within the area which is machined by IBE for 250nm. Similar, Fig. 4(a) shows a cross-sectional sample that is prepared by the focused ion beam and then the central area of this sample is also thinned by an ion milling. Compared with the TEM image of near surface before IBE [Fig. 2(b)], no Beilby layer can be observed. Near surface has no tiny white bits any more. The arrangement of the material particles approaches to the uniformity from the surface to the subsurface, which renders no contrast in between different layers [Figs. 4(b) and 4(c)]. By IBE, a fused silica optic with damage-free near surface is obtained in TEM.
Fig. 4 Cross-sectional HRTEM image showing near surface at 250nm depth of fused silica: (a) fused silica sample after ion milling; (b) and (c) No Beilby layer can be observed in Zone 1 and Zone 2, damage-free machining is obtained by IBE.
3.2. Morphology evolution of nanoparticles
After the trench is polished by IBE on sample surface, the surface morphologies of six areas observed by AFM are obtained. Its roughness values and the surface morphologies of different depths are shown in Fig. 5. There is little visible defect on the initial surface of sample except for subtle polishing trace. The initial roughness value is 0.418nm Root Mean Square (RMS). Because of the existence of residual polishing particles and the subsurface damage in the Beilby layer, as the depth goes up to 50nm, the surface quality becomes worse. It direct-viewing represents the number of the bright spots in the morphology images increases significantly. Therefore, the roughness value increases from 0.418nm RMS to 0.432nm RMS. The Fig. 5(b) image for 50nm depth indicates a much rougher surface than the initial surface. The roughness value of 50nm is 0.432nm RMS, which is the worst. Later, as the depth increases, the surface roughness decreases generally to a level (0.292nm RMS). The surface quality is improved during IBE, due to the smoothing effect induced by ion sputtering at near-normal incidence. When the depth is 250nm, few bright spots exist on the surface.
As the depth goes up to 50nm, the number of “bright spots” increases rapidly to maximum visibly. It could be thought that the Beilby layer has been removed and the nanoscale damage precursors beneath the Beilby layer are exposed totally. When material depth increases, the number of near-surface nanoparticles decreases. And at the 250nm depth, there are few nanoparticles in the measurement.
3.3. Fluorescence spectra analysis
Laser-induced fluorescence of the sample surface at different material depths is examined. The French JY TAU-3 fluorescence spectrometer with an excitation laser of 248nm is used to analyze the chemical structure defects contents at different depth regions of the trench in Fig. 1. We use a 320nm long-pass filter to collect fluorescence spectra for wavelengths above ~400nm in order to avoid the influence of the second diffraction order of the 4.4eV PL band [20].
As shown in Fig. 6, the laser-induced fluorescence emission spectrum of CMP sample surface has two peaks centered at ~440 nm and ~650 nm, which are attributed to the typical defects: the oxygen vacancy defects ODC and the non-bridge oxygen defect NBOHC, respectively [20,21]. The ODC peak fluorescence intensity decreases dramatically when the material depth increases to 100nm. However, when at depth of 100-150nm, The ODC peak fluorescence intensity increases. Later, as the depth increases, the ODC peak fluorescence intensity tends to decrease generally. Meanwhile, it is should be noted that as the material depth goes up to 50nm, the NBOHC peak intensity increases. The sample surface with depth of 0-50nm presents a higher NBOHC peak intensity than other surfaces. Later, the NBOHC peak fluorescence intensity decreases in depth of 50-100nm and it increases in depth of 100-150nm. Eventually, at depth of 200-250nm, the curve of fluorescence intensity information becomes flat in the measurement.
4. Discuss
All Ion beam processing method uses the ion sputtering effect to remove the material and obtain the super-smooth surface (0.292nm RMS). Because of damage-free processing characteristics, IBE can be used to remove material from sample surface to expose near-surface damage precursors. Near-surface nanoscale defects are characterized with nanoparticles and chemical structure defects in section 3. Here we attempt to analyze and discuss the distribution and photothermal absorption performance of near-surface nanoscale defects of fused silica surface after CMP.
From the TEM images, only the Beilby layer is observed. However, near-surface nanoscale defects cannot be distinguished. The underlying reason could be ascribed to the amorphous phase of nanoscale defect layer, same as that matrix, which renders no contrast in between nanoscale defects and matrix. By AFM measurement, the results qualitatively indicate in Fig. 5 that the density/number of nanoparticles extend much deeper than the Beilby layer. To date, there exists few reliable approaches to quantify the density of nanoparticles, but the image processing of counting the pixels of nanoparticles as a makeshift measure can roughly indicate the variation of nanoparticles at varied depths. Here, we follow other researchers to adopt image processing technique [22,23]. The nanoparticles are extracted from the images [Figs. 5(b)–5(f)] first, the size of which is then calculated based on pixels. Finally, the nanoparticles density is represented as a percentage of the pixels of full images (Group 1). In order to improve the accuracy of density estimation, other two parallel experiments (Group 2, 3) on nanoparticles measurement in trench at depth from 50nm to 250nm by AFM are taken. As illustrated in Fig. 7, based on the average values of three groups of data, a fitting curve is obtained. The quantitative density falls exponentially with increasing the depth and when the depth exceeds 250nm the density goes zero meaning that no nanoparticles are present. It is worth mentioning that the nanoparticles size is influenced by the IBE time. In our previous research [11], the size and morphology evolution of near-surface nanoparticles are investigated. And the mechanism of their morphology evolution is attempted to describe. The similar result here indicates that IBE can broaden the nanoparticles width and mitigate the nanoparticles as well. As a result, the ratio of nanoparticles pixels to the whole image will be magnified at deeper depth.
Fig. 7 The relationship between subsurface nanoparticles density and the depth from sample surface. The density drops exponentially with the increase in depth.
For two typical kinds of chemical structure defects, the results in fluorescence spectra analysis reveals that the peak fluorescence intensities of ODC and NBOHC decreases with material depth in general. Based on peak fluorescence intensity and material depth, a liner fit method is used in Fig. 8 to approximately estimate how deep these two types of chemical structure defects extend beneath surface. As illustrated in Fig. 8, the quantitative contents of ODC and NBOHC decrease linearly with increasing the depth. Using linear fit equation in Fig. 8, when the depth from surface exceeds 360nm, the peak fluorescence intensities of ODC is equal to that of NBOHC. The fluorescence intensity curve become flat meaning that no ODC and NBOHC peak fluorescence intensity will be detected.
Fig. 8 The relationships between peak fluorescence (FL) intensities of ODC and NBOHC and the depth from sample surface. All the peak fluorescence intensities drop linearly with the increase in depth.
Therefore, a hypothesis for defect layer model after CMP of fused silica here is offered in Fig. 9. Beneath surface, there exist the Beilby layer of ~20nm. The chemistry and formation of the Beilby layer after CMP are investigated by TEM and a large number of chemical structure defects are characterized [Fig. 2(b) and Fig. 3]. Beneath the Beilby layer, there is a nanoscale defect layer from ~20nm to ~360nm. It contains two types of nanoscale defects: (1) nanoparticles and (2) ODC and NBOHC defects. Depth from ~20nm to ~250nm, the quantitative density of nanoparticles falls exponentially with increasing the depth and the contents of ODC and NBOHC decrease linearly in this depth range, respectively. Depth from ~250nm to ~360nm, there is few nanoparticles in this region. And the contents of ODC and NBOHC continue to decrease until below that which can be reliably detected by fluorescence spectra analysis. Depth exceeding ~360 nm, fused silica matrix appears, which contains some internal material defect clusters only.
Finally, laser damage resistance performances at different depths near surface are carried out. The absorption loss of high-power laser optics causes the deposition of laser energy on surface, which is one of the key factors leading to laser damage. As a non-destructive testing method, the photothermal absorption detection is directly related to the damage precursors, and reflects the damage resistance of the high-peak-power laser optics [13,24,25]. We evaluate the level of surface defects at different material depths by testing photothermal absorption performance. The detection system used in experiment is PTS-2000-RT-C (produced by ZC Optoelectronic Technologies. LTD., China). The values of photothermal absorption analysis parameters are shown in Table 2.
Table 2. Parameters of Photothermal absorption analysis
The surface photothermal absorption of six regions in trench are investigated to calculate the average weak absorption intensity at different material depth. Its photothermal absorption values and the two-dimensional (2D) photothermal absorption distribution of different depths are shown in Fig. 10 and Fig. 11. There are full of visible absorption peaks on the initial surface region. The initial average absorption value is 0.29 ppm and the initial peak value is 0.58 ppm. Later, as the depth increases, the surface average absorption value decreases generally to a level (0.14 ppm). Meanwhile, the number of surface absorption peak decreases evidently. When the depth reaches 250nm, only a few absorption peaks exist on the surface region. The result reveals that the laser damage resistance of fused silica surface goes up effectively with depth increases. However, on the basis of above results, the regularity of peak results is very random. One possible reason could be interference of external environment factors. It is should be noted that he average absorption has a high correlation with zero probability damage thresholds. When the average absorption is below 0.3 ppm, the zero probability damage thresholds will be higher than 30J/cm2 [26].
According to the results in photothermal absorption analysis and the hypothesis for defect layer model after CMP, an overall consideration is necessary to investigate the impact of various nanoscale damage precursors on high fluence laser-induced damage of fused silica optics. It should be noted that when the material depth increases to 50nm, the nanoparticles appear. Its number reaches to the maximum, and the roughness value is worst (0.432nm RMS). The TEM image [Fig. 2(b)] prove that the Beilby layer is about 20nm. Thus, the polishing deposit is removed entirely and all the near-surface defects are exposed at this material depth. When the depth increases further, the density/number of nanoparticles are falls exponentially with increasing depth. The contents of chemical structure defects such as ODC and NBOHC are decreases linearly. The surface quality comes to be improved in the meanwhile (0.292nm RMS). The hypothesis for defect layer model after CMP which contains nanoparticles, chemical structure defects has a good correlation with laser damage resistance property. The improvement of laser damage resistant property implies that the effect on laser-resistant capacity is dominated by the Beilby layer and nanoscale defect layers. When the IBE depth reaches 250nm, the density/number of nanoparticles and the contents of ODC and NBOHC both decreased significantly. Photothermal absorption analysis reveals that the nanoparticles, chemical structure defects in nanoscale defect layer may play an important role in causing a localized optical absorption to lead to laser damage when exposed to sufficient laser fluence. Therefore, advanced post-process technologies are needed to remove the nanoscale defect layer to enhance the laser-resistant capacity of fused silica after CMP.
5. Conclusion
The experiments have something meaningful to clear what are the nature and characteristics of the nanoscale precursors that lead to laser damage initiation after CMP. As a promising detection technology, IBE technology is used to expose the micro-topography of nanosacle damage precursors beneath surface in cross section. There is the Beilby layer (~20 nm) beneath surface of fused silica. TEM/EDS-mapping results show no subsurface damages and material densification phenomenon could be observed. There exist a lot of chemical structure defects in the Beilby layer, and their distribution is uniform. In addition, proved by AFM measurement and fluorescence spectra analysis, there is a nanoscale defect layer (20nm~360nm) beneath the Beilby layer. A hypothesis for defect layer model after CMP of fused silica is offered. In the model, the quantitative density of nanoparticles falls exponentially with increasing the depth and the contents of ODC and NBOHC decrease linearly, respectively. The work has significance in making sense the characteristics of the nanoscale precursors near surface after CMP and conducting post processing technologies to improve laser damage resistance property of fused silica.
Funding
National Natural Science Foundation of China (NSFC) (51835013, U1801259, 51275521, 51775551).
References
1. J. Campbell, R. Hawley-Fedder, C. Stolz, J. Menapace, M. Borden, P. Whitman, J. Yu, M. Runkel, M. Riley, M. Feit, and R. Hackel, “NIF optical materials and fabrication technologies: An overview,” Proc. SPIE 5341, 84–101 (2004). [CrossRef]
2. J. Wong, L. Ferriera, E. F. Lindsey, D. L. Haupt, I. D. Hutcheon, and J. H. Kinney, “Morphology and microstructure in fused silica induced by high fluence UV laser pulses,” J. Non-Cryst. Solids 352(3), 255–272 (2006). [CrossRef]
3. T. I. Suratwala, “Optical fabrication and post processing techniques for improving laser damage resistance of fused silica optics,” in International Optical Design Conference and Optical Fabrication and Testing, OSA Technical Digest (Optical Society of America, 2010), paper OWA1.
4. Y. Li, H. Huang, R. Xie, H. Li, Y. Deng, X. Chen, J. Wang, Q. Xu, W. Yang, and Y. Guo, “A method for evaluating subsurface damage in optical glass,” Opt. Express 18(16), 17180–17186 (2010). [CrossRef] [PubMed]
5. J. Neauport, P. Cormont, P. Legros, C. Ambard, and J. Destribats, “Imaging subsurface damage of grinded fused silica optics by confocal fluorescence microscopy,” Opt. Express 17(5), 3543–3554 (2009). [CrossRef] [PubMed]
6. P. Miller, T. Suratwala, L. Wong, M. Feit, J. Menapace, P. Davis, and R. Steele, “The distribution of subsurface damage in fused silica,” Proc. SPIE 5991, 599101 (2005). [CrossRef]
7. F. Y. Génin, A. Salleo, T. V. Pistor, and L. L. Chase, “Role of light intensification by cracks in optical breakdown on surfaces,” J. Opt. Soc. Am. A 18(10), 2607–2616 (2001). [CrossRef] [PubMed]
8. W. Liao, Y. Dai, Z. Liu, X. Xie, X. Nie, and M. Xu, “Detailed subsurface damage measurement and efficient damage-free fabrication of fused silica optics assisted by ion beam sputtering,” Opt. Express 24(4), 4247–4257 (2016). [CrossRef] [PubMed]
9. T. Suratwala, W. Steele, L. Wong, M. Feit, P. Miller, R. Dylla-Spears, N. Shen, and R. Desjardin, “Chemistry & formation of the Bielby layer during polishing of fused silica glass,” J. Am. Ceram. Soc. 98(8), 2395–2402 (2015). [CrossRef]
10. L. Sun, T. Shao, Z. Shi, J. Huang, X. Ye, X. Jiang, W. Wu, L. Yang, and W. Zheng, “Ultraviolet laser damage dependence on contamination concentration in fused silica optics during reactive ion etching process,” Materials (Basel) 11(4), 577 (2018). [CrossRef] [PubMed]
11. F. Shi, Y. Zhong, Y. Dai, X. Peng, M. Xu, and T. Sui, “Investigation of surface damage precursor evolutions and laser-induced damage threshold improvement mechanism during Ion beam etching of fused silica,” Opt. Express 24(18), 20842–20854 (2016). [CrossRef] [PubMed]
12. L. Sun, H. Liu, J. Huang, X. Ye, H. Xia, Q. Li, X. Jiang, W. Wu, L. Yang, and W. Zheng, “Reaction ion etching process for improving laser damage resistance of fused silica optical surface,” Opt. Express 24(1), 199–211 (2016). [CrossRef] [PubMed]
13. M. Xu, F. Shi, L. Zhou, Y. Dai, X. Peng, and W. Liao, “Investigation of laser-induced damage threshold improvement mechanism during ion beam sputtering of fused silica,” Opt. Express 25(23), 29260–29271 (2017). [CrossRef]
14. J. Bude, P. Miller, S. Baxamusa, N. Shen, T. Laurence, W. Steele, T. Suratwala, L. Wong, W. Carr, D. Cross, and M. Monticelli, “High fluence laser damage precursors and their mitigation in fused silica,” Opt. Express 22(5), 5839–5851 (2014). [CrossRef] [PubMed]
15. X. Gao, G. Feng, J. Han, and L. Zhai, “Investigation of laser-induced damage by various initiators on the subsurface of fused silica,” Opt. Express 20(20), 22095–22101 (2012). [CrossRef] [PubMed]
16. J. Neauport, L. Lamaignere, H. Bercegol, F. Pilon, and J. C. Birolleau, “Polishing-induced contamination of fused silica optics and laser induced damage density at 351 nm,” Opt. Express 13(25), 10163–10171 (2005). [CrossRef] [PubMed]
17. L. Hongjie, H. Jin, W. Fengrui, Z. Xinda, Y. Xin, Z. Xiaoyan, S. Laixi, J. Xiaodong, S. Zhan, and Z. Wanguo, “Subsurface defects of fused silica optics and laser induced damage at 351 nm,” Opt. Express 21(10), 12204–12217 (2013). [CrossRef] [PubMed]
18. J. Trogolo and K. Rajan, “Near surface modification of silica structure induced by chemical/mechanical polishing,” J. Mater. Sci. 29(17), 4554–4558 (1994). [CrossRef]
19. D. Liao, X. Chen, C. Tang, R. Xie, and Z. Zhang, “Characteristics of hydrolyzed layer and contamination on fused silica induced during polishing,” Ceram. Int. 40(3), 4470–4483 (2014). [CrossRef]
20. D. Griscom, “Defect structure of glass,” J. Non-Cryst. Solids 73(1-3), 51–77 (1985). [CrossRef]
21. L. Skuja, M. Hirano, and H. Hosono, “Oxygen-Related Intrinsic Defects in Glassy SiO2: Interstitial Ozone Molecules,” Phys. Rev. Lett. 84(2), 302–305 (2000). [CrossRef] [PubMed]
22. Z. Wang, Y. Wu, Y. Dai, and S. Li, “Subsurface damage distribution in the lapping process,” Appl. Opt. 47(10), 1417–1426 (2008). [CrossRef] [PubMed]
23. T. Suratwala, L. Wong, P. Miller, M. Feit, J. Menapace, R. Steele, P. Davis, and D. Walmer, “Sub-surface mechanical damage distributions during grinding offused silica,” J. Non-Cryst. Solids 352, 5601–5617 (2006). [CrossRef]
24. Z. Wu, P. Kuo, Y. Lu, and S. Gu, “Laser-induced surface thermal lensing for thin film characterizations,” Proc. SPIE 2714, 294–304 (1996). [CrossRef]
25. Y. Tian, F. Shi, Y. Dai, X. Peng, and Y. Zhong, “Laser absorption precursor research: microstructures in the subsurface of mono-crystalline silicon substrate,” Appl. Opt. 56(30), 8507–8512 (2017). [CrossRef] [PubMed]
26. J. Huang, F. Wang, H. Liu, F. Geng, X. Jiang, L. Sun, X. Ye, Q. Li, W. Wu, W. Zheng, and D. Sun, “Non-destructive evaluation of UV pulse laser-induced damage performance of fused silica optics,” Sci. Rep. 7(1), 16239 (2017). [CrossRef] [PubMed]
