Open Access
Add to BibSonomyAbstract
The nano-precursors in the subsurface of Nd:YLF crystal were limiting factor that decreased the laser-induced damage threshold (LIDT) of HfO2/SiO2 high reflection (HR) coatings irradiated from crystal-film interface. To investigate the contribution of electric-field (E-field) to laser damage originating from nano-precursors and then to probe the distribution of vulnerable nano-precursors in the direction of subsurface depth, two 1064 nm HfO2/SiO2 HR coatings having different standing-wave (SW) E-field distributions in subsurface of Nd:YLF c5424181043036123rystal were designed and prepared. Artificial gold nano-particles were implanted into the crystal-film interface prior to deposition of HR coatings to study the damage behaviors in a more reliable way. The damage test results revealed that the SW E-field rather than the travelling-wave (TW) E-field contributed to laser damage. By comparing the SW E-field distributions and LIDTs of two HR coating designs, the most vulnerable nano-precursors were determined to be concentrated in a thin redeposition layer that is within 100 nm from the crystal-film interface.
©2013 Optical Society of America
1. Introduction
Nd:YLF crystal, owing to its low phasefront and polarization distortion, is finding more applications in high-power solid-state lasers [1,2]. Compact and cost efficient resonator designs could be achieved if dielectric mirrors are deposited directly on the end facets of Nd:YLF crystal [3,4]. In such configuration, the laser illuminates HR coatings from crystal-film interface. For the same HR coatings, crystal-film irradiation exhibits much lower LIDTs compared to air-film interface irradiation. Nano-precursors in surface and especially in subsurface of polished Nd:YLF crystal [5] inevitably give rise to the reduced laser damage resistance.
The origin, nature and characteristics of the nano-precursors that lead to laser damage initiation have been extensively studied, especially for case that fused silica optics were subjected to high ultraviolet flux. Polishing residues in the redeposition layers [6–9] and mechanically induced electronic defects in vicinity of cracks in deeper subsurface [10–12] have been identified as damage-initiating nano-precursors to trigger ultraviolet laser damage. These findings promoted sophisticated wet chemical etching process to remove subsurface damage with etch mount up to 50μm [13,14]. But the redeposited silica compounds from the etching solution were also damage-initiating nano-precursors and they were also quite challenging to be removed.
The damage characteristics of HR coatings that are irradiated from Nd:YLF crystal-film interface shares some common features with the widely studied ultraviolet laser damage of fused silica optics but also exhibits certain differences. First, the laser wavelength is in the near infrared region. As the absorptivity of nano-precursors varies with wavelength, the characteristics of near infrared laser damage should be different with that of ultraviolet laser damage. Second, the SW E-field distribution in subsurface repeatedly varies from zero to maximum, which is totally different with the case of bare substrates or substrates coated with antireflection coatings where SW E-field strength in subsurface is almost constant. Some research raised the question that the first-pass TW might be sufficiently absorbed by a nano-precursor to trigger laser damage and to prevent the formation of SW E-field pattern at that location [15]. Whereas, a recent study argued that SW E-field actually affected the damage initiation fluence of gold nanoparticles [16]. The influence of such SW E-field oscillation on damage characteristics of HR coatings irradiated from crystal-film interface is still an issue worth exploring. Moreover, the size of interfacial damage is proportional to the thickness of coatings [17]. From practical point of view, damage size usually plays an important role in the determination of laser damage resistance. Since the total thickness of HR coatings is usually several microns and it is more than 10 times thicker than antireflection coatings, the damage characteristics of HR coatings irradiated from crystal-film interface should be different with substrates or substrates coated with thin antireflection coatings.
Considering from the above analysis, the damage characteristics of HR coatings irradiated from Nd:YLF crystal-film interface was studied to investigate the following issues: 1) Whether the first-pass TW E-field or SW E-filed contributes to the damage initiating from a nano-precursor; 2) Is it possible to probe the locations of vulnerable nano-precursors in subsurface by changing E-filed distributions? 3) Which kind of nano-precursors is more detrimental for exit surface damage? Chemical impurities in redeposition layer or mechanical flaws in deep subsurface, or both kinds of nano-precursors must be removed using tricky and complex etching process.
In this work, SW E-field distributions in subsurface of Nd:YLF crystals were adjusted by changing HR coating designs to find the locations of sensitive nano-precursors in the direction of the subsurface depth. Since the diverse properties of practical nano-precursors may interfere with the analysis of damage test results, 5 and 50 nm gold particles were implanted into the crystal-film interface to obtain reproducible damage behaviors for reference and comparison. The experimental design, sample preparation and laser damage test are described in section 2. Section 3 includes an analysis of the damage test results from the aspect of SW E-field distributions. A summary of our findings appears in section 4.
2. Experiments
2.1 Design of SW E-field distributions in subsurface
At present, it is generally accepted that light absorption in nano-precursors initiates laser damage. When the temperature of a nano-precursor exceeds a critical value, a plasma is created and an increased absorption volume is attained, which then produces macroscopic damage. Here we will not address the whole thermal mechanical damage process but focus on the influence of E-field on the initial damage originating from nano-precursors. Suppose that a nano-precursor is located at a distance z, the power absorbed per unit volume by this nano-precursor in a weakly absorbing medium from a laser pulse with incident intensity I0 is
The absorptivity α can be calculated from the absorption cross section [18], a is the particle radius, and Ei is the incident E-field strength. If the damage occurs during the first pass of the laser beam through the substrate as a traveling wave, the value of |E(z)/Ei|2 inside the substrate is equal to t2. t is the Fresnel transmission coefficientWhere ni is the refractive index of incident medium and nsub is the refractive index of substrate. TW E-field is constant in the substrate and it can’t be adjusted by changing HR coating design. If damage happens as the field evolves to a SW E-field distribution, the value of |E(z)/Ei|2 in the substrate varies from maximum to zero repeatedly and it can be adjusted by modifying HR coating design. Here we devised a way to confirm whether TW E-field or SW E-field contributed to laser-induced damage and to probe whether the vulnerable nano-precursors were concentrated in near-surface region or were randomly distributed along the depth of subsurface.Two quarter-wave stack HR coatings working at 1.064 μm for normal incidence were used in this work. The first design is [Air:(HL)^13:Sub] and the second design is [Air:(HL)^13L:Sub], where H means quarter-wave HfO2 layer, L means quarter-wave SiO2 layer and Sub means Nd:YLF crystal. The refractive indices of HfO2 and SiO2 are 1.962 and 1.453 respectively at 1.064μm. The SW E-field intensity (EFI) distributions of two HR coating designs are given in Figs. 1(a) and 1(b) respectively, and the detailed comparison of two SW EFI distributions in near surface region is given in Fig. 1(c). The shadow regions represent subsurface and the white areas are for thin films. In the subsurface region, the value of SW EFI varies from peak to zero repeatedly after each quarter wave optical thickness for both HR coating designs. The difference between SW EFI distributions of two HR coating designs is: In the region within 100 nm from the crystal surface, SW EFI of the first HR coating is much stronger than that of the second HR coating. And in particular, the first HR coating has maximum SW EFI at crystal-film interface whereas the second HR coating has near zero SW EFI at this interface.
Fig. 1 SW EFI distributions in HR coatings and subsurface of Nd:YLF crystals. (a) SW EFI distribution of [Air:(HL)^13:Sub] design. (b) SW EFI distribution of [Air:(HL)^13L:Sub] design. (c) Detailed comparison of SW EFI distributions in the shallow subsurface region between two HR coating designs. Shaded areas denote substrate medium.
We can predict, if TW E-field causes laser-induced damage or the vulnerable nano-precursors are randomly distributed along the depth of subsurface, the damage resistance of these two HR coatings will be similar. If SW E-field gives rise to laser-induced damage and the vulnerable nano-precursors are concentrated in the shallow subsurface region, the damage resistance of the first HR coating will be much lower. By comparing the laser damage resistance of two kinds of HR coatings, we can distinguish whether SW or TW E-filed causes damage initiating from nano-precursors and can probably ascertain the locations of the vulnerable nano-precursors.
2.2 Preparation of HfO2/SiO2 HR coatings and artificial defects
In practice, the properties of nano-precursors are quite diverse and the laser-induced damage is probabilistic. Such complex situation has promoted researches using artificial defects with known size and absorptivity [19–21]. To better understand the behaviors of laser damage initiating from nano-precursors, gold nano-particles were used in this work to study the damage characteristics in a more reliable way. Gold nano-particles with nominal diameters of 5 and 50 nm from Ted Pella Inc. were used in this study. The coefficient of diameter variation for both gold particles is about 11%.
Nd:YLF substrates were first carefully cleaned by ultrasonic cleaning process [22]. Then, 5 and 50 nm gold particles were respectively dispersed on the cleaned Nd:YLF substrate surface by spin coating process. Because it is very difficult to observe such small particles using optical microscope, the areal density of gold particles will be roughly estimated from the density of damage sites. The above two kinds of HR coatings are deposited on three kinds of Nd:YLF substrates using electron beam evaporation process. Figure 2 shows the schematic of one kind of HR coatings and artificial defects. The details of the electron beam evaporation process have been given in another paper [23]. The absorption of two kinds of HR coatings is below 10 parts per million at 1.064 μm.
Fig. 2 Schematic of [Air:(HL)^13L:Sub] HR coatings on (a) blank Nd:YLF substrate, (b) Nd:YLF substrate with 5 nm gold particles pre-deposited on surface, (c) Nd:YLF substrate having 50 nm gold particles pre-deposited on surface.
2.3 Laser damage test and characterization techniques
The prepared HR coatings were irradiated from the crystal-film interface by 1.064 μm, 10 ns pulses from a Nd:YAG laser having a TEM00 mode, a beam diameter of 1mm and a repetition rate of 10 Hz. An angle of incidence was chosen slightly off normal, at 3°. The raster scan method [24] was adopted to obtain the LIDTs of HR coatings. Two 4 × 4 mm2 scan areas were used to get the average LIDTs of HR coatings. The laser fluence started from 0.5 J cm−2 and first increased to 5 J cm−2 with a 0.5 J cm−2 increment, after that it increased to the “damage fluence” with a 2 J cm−2 increment. The damage morphologies could be modified by the multiple irradiations during the raster scan test, so a single shot method was used to obtain representative damage morphologies of the prepared HR coatings, where a specific fluence based on previous raster scan test was used. The damage morphologies of HR coatings were first identified by a Nomarski microscope and were then characterized using scanning electron microscopy.
3. Results and discussion
LIDTs of two kinds of HR coatings that were deposited on three different kinds of Nd:YLF substrates are given in Table 1. To highlight the contribution of E-field on laser damage initiating from nano-precursors, Table 1 also gives the value of EFI at crystal-film interface where is the location of gold particles.
Table 1. LIDTs of two kinds of HR coatings
In order to probe the location of sensitive nano-precursors in subsurface, it is necessary to first distinguish whether the TW or SW E-field contributes to the laser damage. To address this problem, the LIDTs of two kinds of HR coatings on Nd:YLF substrates with 5 nm gold particles are discussed first. The two kinds of HR coatings have identical TW EFI but totally different SW EFI at the location of 5 nm gold particles. If TW E-field causes laser-induced damage, the LIDTs of two kinds of HR coatings should be very similar. However, the LIDT of [Air:(HL)^13L:Sub] HR coatings was almost 9 times higher than that of [Air:(HL)^13:Sub] HR coatings. Lower SW EFI at the location of gold particles resulted in higher LIDT, which reveals that it is SW E-field rather than TW E-field that contributes to the nanosecond pulse laser damage initiating from nano-precursors.
Figure 3 shows the representative damage morphologies of two kinds of HR coatings on Nd:YLF substrates having 5 nm gold particles. For [Air:(HL)^13:Sub] HR coatings whose SW EFI at crystal-film interface is about 400%, there were intensive damage sites in the area of laser spot as given in Fig. 3(a). The average areal density of 5 nm gold particles was thought to be around thousands per square millimeter, which is high enough to reflect the representative damage characteristics. Figure 3(b) presents an enlarged micrograph of damage sites. These are typical round flat bottom pits initiating from 5 nm gold particles, the depth of the damage sites is the film thickness. The circular geometry of pits is consistent with the model describing laser damage initiating from nano-precursors. When a nano-precursor is exposed to a laser beam of sufficient energy, it creates intense plasma, generates considerable pressure, induces highly tensile stress and causes the coating layers to delaminate. The origin of the gold particles should be at the center of the damage sites but was not clearly visible. Laser-induced damage is determined by the joint contribution from the absorptivity of nano-precursors and SW EFI. When SW EFI was close to zero, even highly absorbing 5 nm gold particles could not trigger laser damage at high fluence of 18 J cm−2. Moreover, this result also suggests that 5 nm gold particles did not cause noticeable SW E-field modulations in the nearby region of the particles. Comparatively, Fig. 3(c) gives the typical damage morphology of [Air:(HL)^13L: Sub] HR coatings whose SW EFI at crystal-film interface is about zero. The density of damage site is very low, and the diameter of damage sites is usually more than 100 um. Figure 3(d) shows that the depth is about 40 μm. Compared to damage morphologies in Fig. 3(a), we can determine that nano-precursors in the deep subsurface rather than 5 gold particles caused the observed catastrophic damage.
Fig. 3 Representative damage morphologies of two kinds of HR coatings on Nd:YLF substrate with 5 nm gold particles pre-deposited on surface. (a) Low magnification SEM micrograph of [Air:(HL)^13:Sub] HR coatings reflects the high density of damage sites. (b) High magnification SEM micrograph shows the detailed morphologies of damage sites. (c) Optical photograph of a damage site of [Air:(HL)^13L:Sub] HR coatings obtained using Nomarski microscope. (d) Surface topography of a damage site obtained using Veeco DEKTAK Profilometer.
It is also interesting to explore the influence of diameter of gold particles on damage characteristics. For both HR coatings, SW EFI at the location of 50 nm gold particles was strong enough to cause laser damage at low fluence. Since particle absorptivity increases linearly with particle radius at this diameter range [25], 50 nm gold particles resulted in lower LIDTs compared to 5 nm gold particles.
Figure 4 shows that damage morphologies initiating from 50 nm gold particles for both kinds of HR coatings are similar. And an interesting observation is that a tiny melting point is clearly visible at bottom of most damage sites, which should be the location of a 50 nm gold particle. The observed tiny melting point indicates that local temperature in vicinity of 50 nm gold particles is higher than local temperature at 5 nm gold particles. In addition, the asymmetrical damage morphologies suggest that temperature gradient and associated stress distribution in the region surrounding 50 nm gold particles were non-isotropic. However the reason for such non-isotropic delamination is still not well understood by ourselves, here we just highlight that there is a certain difference between the detailed damage process originating from 5 and 50 nm gold particles.
Fig. 4 Representative damage morphologies of two kinds of HR coatings on Nd:YLF substrates with 50 nm gold particles pre-deposited on surface. (a) Low magnification SEM micrograph of [Air:(HL)^13:Sub] HR coatings reflects the high density of damage sites. (b) High magnification SEM micrograph shows the detailed morphologies of damage sites. (c) Low magnification SEM micrograph of [Air:(HL)^13L:Sub] HR coatings reflects the high density of damage sites. (d) High magnification SEM micrograph shows the detailed morphologies of damage site.
After knowing the behaviors of laser damage originating from 5 and 50 nm gold particles, the damage characteristics of HR coatings on blank Nd:YLF substrates can be better understood now. Table 1 shows that the LIDT of [Air:(HL)^13L:Sub] HR coating is 20 J cm−2, which is about 5 times higher than LIDT of [Air:(HL)^13:Sub] HR coating. Comparing the LIDTs and SW EFI distributions in the shallow subsurface region of two HR coatings, we confirm that the vulnerable nano-precursors are concentrated in a shallow subsurface region that is within 100 nm from crystal-film interface for the used Nd:YLF substrates. Such a shallow region in subsurface probably corresponds to the well-known redeposition layer of polished optics, where concentration of polishing compound components typically decays exponentially to a depth of 20-200 nm [7,15].
Figure 5(a) shows the damage morphology of [Air:(HL)^13:Sub] HR coating, and it is very similar to Fig. 3(b). The C polishing residues probably contributed to the observed laser damage because of the use of nano-diamond-powders in the final polishing process of Nd:YLF crystals. The characteristics of laser damage originating from practical nano-precursors is similar to that originating from 5 nm gold particles rather than bigger 50 nm gold particles [26]. Moreover, the vulnerability of practical nano-precursors is almost comparable to that of 5 nm gold particles, because the LIDTs of [Air:(HL)^13:Sub] HR coatings on blank Nd:YLF substrates and Nd:YLF substrates with 5 nm gold particles are similar. For [Air:(HL)^13L:Sub] HR coatings, the damage morphologies in Fig. 5(b) is very similar to Fig. 3(c), which suggests that it is a nano-precursor in the deep subsurface region that caused laser damage. Previous investigation of 351 nm laser damage in SiO2 thin films with 18.5 nm gold particles has found that the LIDTs increased with increasing particle-lodging depth. And it was explained from the aspect that deeper lodging depth requires a larger amount of energy to form craters [27]. But we don’t think that lodging depth difference is the reason that two HR coating designs had quite different LIDTs. The thickness of HR coatings is several microns and it is more than 10 times thicker than the thickness of redeposition layer. When the lodging depth of nano-precursors changes for hundreds of nanometers, the energy required to form the craters does not vary a lot. So the 5 times higher LIDTs and lower density of damage sites reveals that the density and absorptivity of nano-precursors in deeper subsurface are much less than these of polishing residues in the redeposition layer whose thickness is less than 100 nm.
Fig. 5 Representative damage morphologies of two kinds of HR coatings on Nd:YLF substrate. (a) SEM micrograph of a damage site of [Air:(HL)^13:Sub] HR coating. (b) The optical photograph of a damage site of [Air:(HL)^13L:Sub] HR coating.
Except for polishing residues in the redeposition layer, cracks in the surface and subsurface or contaminations on the substrate surface due to inadequate cleaning may also contribute to the interfacial damage between the coating and the substrate. It is worth to discuss whether these two factors played a role in the observed laser damage. Nd:YLF substrates used in this work were polished with the surface quality better than 10-5 S/D. Using Nomarski microscope with 200 times magnification, only a few thin scratches were visible in the clear aperture region. For both kinds of HR coatings on the Nd:YLF substrates, damage did not preferentially occur at these thin scratches but appeared randomly in the raster scan area. We think that this reflects that nano-precursors in vicinity of thin cracks are not more detrimental than nano-precursors in redeposition layer. In addition, Nd:YLF substrates were carefully cleaned using our ultrasonic cleaning process before deposition. Even if there were contaminations left on the substrate surface, the contaminations should be localized with a very low density. For both kinds of HR coatings on Nd:YLF substrates, hundreds of sites that were tested showed consistent damage behaviors. There was no sign that localized surface contaminations affected the representative damage characteristics.
For the case of HR coatings irradiated from crystal-film interface, we finally reach a conclusion that the vulnerable nano-precursors are concentrated in the redeposition layers that is within 100 nm from the crystal-film interface for the used Nd:YLF substrates. It is worth to note that this conclusion has its limit. It is more applicable to interfacial damage between thick coatings and substrates, for example, HR coatings irradiated from substrate-film interface, polarizers, dichroic mirrors et al. than thin antireflection coatings or substrates. When the same kind nano-precursors in redeposition layers trigger laser damage at the same fluence, thicker coatings exhibit larger damage size. For thin antireflection coatings or substrates, the initial damage size originating from nano-precursors in redeposition layers is extremely small. If damage size is an affecting factor when determining LIDT or the damage system has inadequate detection size, thin antireflection coatings or substrates would appear to have higher LIDTs compared to thick coatings. In other words, nano-precursors in the redeposition layers have a more significant impact on LIDT of thick coatings than thin antireflection coatings or substrates.
We can predict that shallow etching with depth up to hundreds of nanometers is enough to significantly increase the LIDT of HR coatings irradiated from crystal-film interface. If no contaminant is repreciptating onto the surface of the etched substrates, the LIDTs of the two kinds of HR coatings will be similar. Alternatively, significant LIDT improvement could also be achieved by reducing SW EFI at locations where the absorptivity and density of nano-precursors are very high. Complex chemical etching that removes the whole subsurface definitely can further increase the LIDT, but it is not cost-effective compared to shallow etching.
4. Conclusion
The damage characteristics of HfO2/SiO2 HR coatings irradiated from crystal-film interface by 1064 nm nanosecond pulse laser has been studied in a comparative manner using different SW E-field designs and artificial gold nano-particles. Lower SW EFI at the location of 5 nm gold particles resulted in higher LIDT, which convincingly shows that it is the SW E-field rather than TW E-field that contributes to the laser-induced damage originating from nano-precursors. Then an approach taking advantage of SW E-field oscillations has been devised to probe the location of vulnerable nano-precursors that initiates interfacial damage between HR coatings and Nd:YLF crystals. Higher SW EFI in the shallow subsurface region leads to lower LIDTs, which suggests that the vulnerable nano-precursors are concentrated in a very thin region that is within 100 nm from the crystal-film interface. And this provides valuable information for selecting efficient etching process to increase LIDT.
Acknowledgments
This work was partly supported by the National Natural Science Foundation of China (Grant Nos. 61235011, 61008030, 61108014, 61205124), the Specialized Research Fund for the Doctoral Program of High Education (Grant No. 20100072120037) and the National 863 Program.
References and links
1. Y. J. Huang, Y. S. Tzeng, C. Y. Tang, Y. P. Huang, and Y. F. Chen, “Tunable GHz pulse repetition rate operation in high-power TEM00-mode Nd:YLF lasers at 1047 nm and 1053 nm with self mode locking,” Opt. Express 20(16), 18230–18237 (2012). [CrossRef] [PubMed]
2. C. Y. Cho, Y. P. Huang, Y. J. Huang, Y. C. Chen, K. W. Su, and Y. F. Chen, “Compact high-pulse-energy passively Q-switched Nd:YLF laser with an ultra-low-magnification unstable resonator: application for efficient optical parametric oscillator,” Opt. Express 21(2), 1489–1495 (2013). [CrossRef] [PubMed]
3. V. Besotosnii, E. Cheshev, M. Gorbunkov, P. Kostryukov, M. Krivonos, V. Tunkin, and D. Jakovlev, “Diode end-pumped acousto-optically Q-switched compact Nd:YLF laser,” Appl. Phys. B 101(1–2), 71–74 (2010). [CrossRef]
4. W. C. Schwartz, J. Harrison, and P. F. Moulton, “A Diode-Pumped, Solid State Nd:YLF Laser for Micro-Machining,” http://www.qpeak.com/Meetings/ICALEO%201996%20MPS%20micromachining.pdf.
5. S. Chatterjee, “Simple technique for polishing laser rods,” Opt. Eng. 42(4), 1076–1083 (2003). [CrossRef]
6. R. C. Estler, N. S. Nogar, and R. A. Schmell, “The Detection, Removal and Effect on Damage Thresholds of Cerium Impurities on Fused Silica,” Natl. Bur. Stand (U.S.), Spec. Publ. 775, 183–188 (1989).
7. M. R. Kozlowski, J. Carr, I. Hutcheon, R. Torres, L. Sheehan, D. Camp, and M. Yan, “Depth profiling of polishing-induced contamination on fused silica surface,” Proc. SPIE 3244, 365–375 (1998). [CrossRef]
8. J. Yoshiyama, F. Genin, A. Salleo, I. Thomas, M. Kozlowski, L. Sheehan, I. Hutcheon, and D. Camp, “Effects of Polishing, Etching, Cleaving, and Water Leaching on the UV Laser Damage of Fused Silica,” Proc. SPIE 3244, 331–340 (1998). [CrossRef]
9. 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]
10. T. Laurence, J. Bude, N. Shen, T. Feldman, P. Miller, W. Steele, and T. Suratwala, “Metallic-Like Photoluminescence and Absorption in Fused SilicaSurface Flaws,” Appl. Phys. Lett. 94(15), 151114 (2009). [CrossRef]
11. P. E. Miller, J. D. Bude, T. I. Suratwala, N. Shen, T. A. Laurence, W. A. Steele, J. Menapace, M. D. Feit, and L. L. Wong, “Fracture-induced subbandgap absorption as a precursor to optical damage on fused silica surfaces,” Opt. Lett. 35(16), 2702–2704 (2010). [CrossRef] [PubMed]
12. J. Fournier, J. Néauport, P. Grua, E. Fargin, V. Jubera, D. Talaga, and S. Jouannigot, “Evidence of a green luminescence band related to surface flaws in high purity silica glass,” Opt. Express 18(21), 21557–21566 (2010). [CrossRef] [PubMed]
13. T. I. Suratwala, P. E. Miller, J. D. Bude, W. A. Steele, N. Shen, M. V. Monticelli, M. D. Feit, T. A. Laurence, M. A. Norton, C. W. Carr, and L. L. Wong, “HF-based etching processes for improving laser damage resistance of fused silica optical surfaces,” J. Am. Ceram. Soc. 94(2), 416–428 (2011). [CrossRef]
14. P. E. Miller, T. I. Suratwala, J. D. Bude, T. A. Laurence, N. Shen, W. A. Steele, M. D. Feit, J. A. Menapace, and L. L. Wong, “Laser damage precursors in fused silica,” Proc. SPIE 7504, 75040X, 75040X-14 (2009). [CrossRef]
15. B. E. Newnam, D. H. Gill, and G. Faulkner, “Influence of Standing Wave Fields on the Laser Damage Resistance of Dielectric Films,” Natl. Bur. Stand (U.S.), Spec. Publ. 435, 254–271 (1976).
16. S. Papernov and A. W. Schmid, “Correlations between embedded single gold nanoparticles in SiO2 thin film and nanoscale crater formation induced by pulse-laser radiation,” J. Appl. Phys. 92(10), 5720–5728 (2002). [CrossRef]
17. C. J. Stolz, J. A. Menapace, K. I. Schaffers, C. Bibeau, M. D. Thomas, and A. J. Griffin, “Laser damage initiation and growth of antireflection coated S-FAP crystal surfaces prepared by pitch lap and magnetorheological finishing,” Proc. SPIE 5991, 59911I, 59911I-7 (2005). [CrossRef]
18. H. C. van der Hulst, Light scattering by small particles (John Wiley and Sons, 1957).
19. S. Papernov, A. Tait, W. Bittle, A. W. Schmid, J. B. Oliver, and P. Kupinski, “Near-ultraviolet absorption and nanosecond-pulse-laser damage in HfO2 monolayers studied by submicrometer-resolution photothermal heterodyne imaging and atomic force microscopy,” J. Appl. Phys. 109(11), 113106 (2011). [CrossRef]
20. J. Y. Natoli, L. Gallais, B. Bertussi, A. During, M. Commandré, J. L. Rullier, F. Bonneau, and P. Combis, “Localized pulsed laser interaction with submicronic gold particles embedded in silica: a method for investigating laser damage initiation,” Opt. Express 11(7), 824–829 (2003). [CrossRef] [PubMed]
21. P. Jonnard, G. Dufour, J. L. Rullier, J. P. Morreeuw, and J. Donohue, “Surface density enhancement of gold in silica film under laser irradiation at 355 nm,” Appl. Phys. Lett. 85(4), 591–593 (2004). [CrossRef]
22. Z. X. Shen, T. Ding, X. W. Ye, X. D. Wang, B. Ma, X. B. Cheng, H. S. Liu, Y. Q. Ji, and Z. S. Wang, “Influence of cleaning process on the laser-induced damage threshold of substrates,” Appl. Opt. 50(9), C433–C440 (2011). [CrossRef] [PubMed]
23. X. B. Cheng, J. L. Zhang, D. Tao, Z. Y. Wei, H. Q. Li, and Z. S. Wang, “The effect of an electric field on the thermomechanical damage of nodular defects in dielectric multilayer coatings irradiated by nanosecond laser pulses,” Light: Sci. Appl. 2, e80 (2013), doi:. [CrossRef]
24. M. R. Borden, J. A. Folta, C. J. Stolz, J. R. Taylor, J. E. Wolfe, A. J. Griffin, and M. D. Thomas, “Improved method for laser damage testing coated optics,” Proc. SPIE 5991, 59912A, 59912A-10 (2005). [CrossRef]
25. M. D. Feit and A. M. Rubenchik, “Implications of nanoabsorber initiators for damage probability curves, pulselength scaling and laser conditioning,” Proc. SPIE 5273, 74–82 (2004). [CrossRef]
26. L. Gallais, J. Capoulade, J. Y. Natoli, and M. Commandré, “Investigation of nanodefect properties in optical coatings by coupling measured and simulated laser damage statistics,” J. Appl. Phys. 104(5), 053120 (2008). [CrossRef]
27. S. Papernov, A. Tait, W. Bittle, A. W. Schmid, J. B. Oliver, and P. Kupinski, “Two mechanisms of crater formation in ultraviolet-pulsed-laser irradiated SiO2 thin films with artificial defects,” J. Appl. Phys. 97(11), 114906 (2005). [CrossRef]
