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The schematic diagram of raster scanning damage testing protocol. The adjacent laser spots in each region overlapped 90% in radial direction.
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Scratches in fused silica are notorious laser damage precursors to UV laser damage initiation. Ductile and brittle scratches were intentionally generated using various polishing slurries. The distribution, profile and the dimension of scratches were characterized. The damage resistance of polished surfaces was evaluated using raster scanning damage...
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... The LIDT value of the double-layer AR coating is 2.24 J·cm − 2 , slightly lower than that of the bottom layer of 2.58 J·cm − 2 and the top layer of 2.32 J·cm − 2 , which may be due to the different thermal energy absorption of different lms [22]. It should be noted that the LIDT of the double-layer coating matches the reported values of 1.5-10 J•cm − 2 (355 nm, 6-10 ns) for oxide optical materials [23][24][25], and the proposed coating can meet the basic application requirements of ultraviolet lasers. ...
A double-layer broadband antireflection (AR) coating with excellent transmittance at 250–400 nm has been designed and prepared by the sol-gel method. The quarter-half double-layer structure is optimized with the aid of Filmstar thin film design software. Mesoporous SiO 2 film templated by an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer is used as the top layer, and a ZrO 2 -SiO 2 hybrid film with matching refractive index is employed as the bottom layer. 1H, 1H, 2H, 2H-Perfluorodecyltriethoxysilane is used to modify the surface of the AR coating, which greatly improves the environmental stability of the coating. The obtained double-layer AR coating can achieve an average transmittance of 99.34% in the wavelength range of 250–400 nm. The laser induced damage threshold of the coating is measured using a 355 nm laser (pulse width: 6.4 ns), and the results show that the damage threshold is 2.24 J·cm − 2 . This study provides a new way for the preparation of UV AR coatings with good optical performance and environmental stability.
... Despite continued improvements in damage performance, the surface damage threshold of the components is still far below the intrinsic bulk limit of the material [6]. Recent work shows there are many sources of laserinduced damage to fused silica components, such as scratches [7], subsurface defects [8], inclusions [9], damage precursors [10], and surface contamination [11,12], which cause the most significant reduction in the laser-induced damage threshold (LIDT) of fused silica [13]. These near-surface defects (damage precursors) can absorb the subband-ccgap light, leading to damage to optical materials. ...
Aerosol particle contamination in high-power laser facilities has become a major cause of internal optical component damage resistance and service life reduction. In general, contaminating particles primarily originate from stray light; therefore, it is crucial to investigate the mechanism and dynamics of the dynamic contaminating particle generation to control the cleanliness level. In this study, corresponding research was conducted on experiments and theory. We investigated the particle generation and surface composition modification under the action of a laser. We employed various surface analytical methods to identify the possible variations in the aluminum alloy surface during laser irradiations. A theoretical model for particle ejection from aluminum alloy surfaces was established by taking the adhesion force and laser cleaning force (due to thermal expansion) into account. The results show that the threshold energies for contamination particle generation and damage are around 0.1 and 0.2 J/cm2, respectively. Subsurface impurities are the primary source of particles, and particle adhesion density is related to surface roughness. Pollution particle generation and splashing processes include temperature increases, phase changes, impact diffusion, and adhesion. The results provide a reference for the normal operation of high-energy laser systems. The results also suggest that the laser irradiation pretreatment of aluminum alloy surfaces is essential to improve the cleanliness level.
... Ye et al. [24] used FDTD to study the effect of scratches on the electric field on the surface of bulk fused silica, and the model was in two dimensions. They used a perfectly matched layer (PML) boundary at the left and right borders and used a scattering boundary at the top and bottom borders. ...
... In [24], Ye et al. studied the effect of three types of scratches (triangular, serrated, and parabolic) on the electric field and found that the electric field intensity increased with the depth and width of the scratch, and the parabolic scratch enhanced the electric field most obviously. But they did not explain the mechanism by which the scratches modulate the electric field nor did they consider the effect of multiple scratches. ...
The scratches on the fiber end face can enhance the local electrical field, which lowers the damage threshold. The damage mechanism of a high-energy laser is investigated. The effect of scratches on the electric field is simulated by the finite difference time domain (FDTD) solution. The results show that the depth of the scratch has a greater ability to influence the electric field than the width, and multiple scratches have a stronger modulation than a single scratch. In calculation, the damage threshold of the scratch-free end face is $0.456\;{{\rm J/cm}^{2}}$ 0.456 J / c m 2 when the incident light electric field intensity is $50 \; {\rm MV/cm}$ 50 M V / c m , compared to $0.345\;{{\rm J/cm}^{2}}$ 0.345 J / c m 2 in the presence of the scratch on the end face.
... Wang et al. found that etching-induced deposits with nanometer to micron diameters are composed of metallic salts, and the laser-induced damage threshold (LIDT) in the area with a high density of deposits is much lower than that with no deposits [9]; Ye et al. deposited fused silica with micron-sized particles using an HF buffered solution, deteriorating the surface LIDT from ∼33 to ∼11 J/cm 2 at 3 ns [10]. Light field enhancement due to surface deposited particles is a key factor triggering laser damage since incident laser energy and optics laser absorption would increase with light field intensity [11][12][13]. Therefore, the response of the light field intensity to the surface deposits of the optics is supposed to be clarified to mitigate/eliminate adverse deposits and improve the laser damage resistance of fused silica. ...
... According to Fresnel's law, light intensity I and electric strength E meet the equation I ∝ E 2 [11,18]. The LIF can be expressed using the ratio of the modulated light I m inside fused silica stimulated by the deposited particle to light intensity I 0 in undeposited fused silica; therefore, LIF = I m /I 0 = (E m /E 0 ) 2 . ...
... E m and E 0 represent the peak electric intensity in the glass bulk, which are modulated by the deposited surface and the smooth surface, respectively, and E 0 is proven to be ∼1.19 V/m [11]. Figure 8 demonstrates the LIF discrepancy between deposited Fig. 8. LIF difference between the deposited particles irradiated with lasers from different directions. ...
Deposited substances generated from hydrofluoric acid based (HF-based) etching are found to be the precursors that deteriorate the resistance of fused silica optics to laser damage. In this paper, the surface of polished fused silica was treated with a buffer oxide etchant (BOE, 5–10%wt. HF $+ $ + 10%wt. ${\rm{NH}}_4{\rm F}+80{-}85\%{\rm wt.}\, {\rm H}_2{\rm O}$ N H 4 F + 80 − 85 % w t . H 2 O ). The optic surface area affected by the etching-induced deposits $({\rm NH}_4){\rm SiF}_6$ ( N H 4 ) S i F 6 was found to increase significantly with the amount of material removal and sensitivity to the post-cleaning procedure. Three shapes of deposited particles are simultaneously identified on the treated samples. The 3D finite-difference time-domain (FDTD) was used to simulate the light field distribution near the deposited particles, which demonstrates that fused silica is subject to more light modulation when a particle is exposed on the front surface laser than on the rear surface laser. In addition, dense particles barely increase the light intensification factor (LIF) while markedly increase the light focused probability inside fused silica. Moreover, a multiple linear regression (MLR) analysis for the LIF builds a fitting plane model of the LIF and the particle height as well as the horizontal size, revealing that the LIF increases with the size of the deposited particle, especially its height. The laser damage testing results indicate that a deposited layer of $\sim 76\; {\rm nm}$ ∼ 76 n m in height had little influence on the laser-induced damage threshold (LIDT) of the optics and larger deposited particles with up to 9 µm thickness may deteriorate the LIDT to 41.62% that of the reference sample. Both the simulation and experimental results demonstrate that deposited particles with a height of more than 0.1 µm should be inhibited to achieve fused silica with superior laser damage performance.
... The light modulation was found to be significantly affected by the geometric factors of scratches/cracks, such as their size as well as shape. 4,24 As it has reported above, both the morphology and the dimension of grinding-induced cracks are modified markedly due to chemical etching. Therefore, clarifying the influence of evolved cracks on light modulation is of great importance in optimizing manufacturing processes to improve the processing efficiency as well as the laser damage resistance of fused silica, since the etching condition, which is favor of decelerating light modulation, could be determined and adopted. ...
The mechanical defects (scratches/cracks) originated from grinding processing need to be dislodged so that improving the optical performance of fused silica. In this paper, HF‐based (HF represents hydrofluoride acid) etchant was used as a subsequent fabrication for loose‐abrasive ground fused silica, and the surface morphology and characteristics of samples were evaluated, meanwhile, the electric/light field distribution around treated cracks was simulated using the finite difference time domain (FDTD) method. The results show that sufficient material removal amount blunts the cracks to be a series of parabolic‐shaped and smooth craters fused with each other, whose diameter and depth grow as a power function with etched depth. Triple subsurface defect depth should be removed so as to mitigate surface roughness to be ∼2.46 µm and promote transmission from initial 22.55%–54.02%. FDTD simulation results reveal that deep etching alleviates the light intensification factor (LIF) of craters within 1.8 as the diameter‐to‐depth ratio of craters is increased over 10. Moreover, a thickness removal model of ground fused silica involving the cracks distribution characteristics, cracks etching behavior as well as the LIF variation of craters is established, in which the supposed etched depth is determined to promote the manufacturing efficiency and laser damage resistance of the material.
... The ridge width of the first layer is larger than that of the second layer. The refractive index of fused silica [30,31] is n 1 =1.45, and the refractive index of air is n 2 =1.00. ...
A T-shaped reflective grating device under the second Bragg angle is proposed for polarizer. This grating device is mainly made of fused silica with T-shaped ridges, which can diffract the energy of the TE-polarized light and the TM-polarized light to the −2nd order and the 0th order with the reflective efficiency of each order more than 95%. Normalized field magnitude distribution and overlap integral are analyzed to explain the physical mechanism and energy exchange. Based on the optimized results, the beam splitter exhibits high efficiency, good extinction ratio and optical properties of the incident bandwidth. Moreover, grating can have longer period for easy fabrication under second Bragg incidence compared to reported Bragg incidence. Therefore, the T-shaped reflective grating device should be useful for the future optical communication industry.
... Modeling is conducted in two-dimensional model, and the simulation domain is set as x (60 μm) × y (10 μm) in area, in which the back surface of silica was covered with a 0.5 μm air layer. To avoid obvious wave reflection at the boundaries of the model, an absorbent layer called PML (perfectly-matched-layer) is placed on the left and right borders, and an ideal absorption boundary called scattering boundary on the up and down borders [4,16]. Figure 1 shows the AFM images of brittle scratches at 750mN before and following chemical etching. ...
... According to Fresnel's law, the light field intensity I i and the electric field intensity E i meets the equation I i = E i 2 in a single medium [16]. In order to rank the light modulation of various rear scratches and evaluate their LIDT influence levels, the light intensification factor (LIF) is defined as the ratio of the peak light intensity I max to the intensity of defectfree bulk I 0 = 1.19 2 , as is defined in Ref. [16] LIF = I max /I 0 . ...
... According to Fresnel's law, the light field intensity I i and the electric field intensity E i meets the equation I i = E i 2 in a single medium [16]. In order to rank the light modulation of various rear scratches and evaluate their LIDT influence levels, the light intensification factor (LIF) is defined as the ratio of the peak light intensity I max to the intensity of defectfree bulk I 0 = 1.19 2 , as is defined in Ref. [16] LIF = I max /I 0 . We calculate the LIF of real scratches before and after etching, and the results are shown in Table 1, in which LIF in silica is found to increase significantly due to etching. ...
Brittle scratches are responsible for the damage ignition when exposed to pulsed UV laser. We investigated the morphology evolution and damage resistance of glass with HF etching. The light intensity around scratches is found to increase with the dimension of scratches. Laser damage tends to be initiated at scratches edge and this is correlated with the peak electrical/light intensification and/or the mechanical weakening due to the chevron-cracks along the scratch. Moreover, the laser-induced damage threshold (LIDT) fluctuates when the length of chevron cracks varied and/or the electric/light intensification factor (LIF) is increased with the size of scratches in chemical etching.
... Three cracks in each area with different damage density were selected for the simulation, and the mean value of the electric field amplitude is taken as the value of the region. According to Fresnel's law, the light field intensity I and the electric field intensity E meet the equation I = E 2 [18,29]. The LIEF is defined as the ratio of the peak electric intensity I max to the peak intensity of the electric field value in the substrate, so LIEF = I max /I 0 . ...
The laser-induced damage threshold (LIDT) of fused silica is affected by laser field intensity modulation and laser energy absorption. In this paper, the subsurface damage (SSD) density and morphology are detected by the small-angle taper polishing method. The modulation effect of SSD morphology on the incident laser/electric field is analyzed by the finite difference time domain (FDTD) simulation. Finally, the LIDT of the taper polished surface is tested to analyze the relationship among LIDT, SSD density, and SSD morphology, and the results show a high correlation. A reliable regression model is obtained based on the results, which shows that LIDT is inversely proportional to SSD density and the light intensity enhancement factor (LIEF).
