Laser induced damage due to scratches in the surface of nonlinear optical crystals KH2PO4 (KDP)

Zhu, Dexing; Li, Yaguo; Zhang, Qinghua; Wang, Jian; Xu, Qiao

doi:10.1186/s41476-017-0062-8

Cited by 12 publications

(6 citation statements)

References 21 publications

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“…Although the light intensity distribution caused by the triangular scratch is more complex and intense than that of the circular scratch due to the existence of manufacturing-induced front surface scratches, the LIEF of scratches is still smaller than that of cracks, which is similar to reference [20]. As shown in Figure 12c, Zhu et al [79] investigated the influence of surface scratches on the incident light intensity of KDP and found that once the brittle cracks appeared on the side of scratches, the LIEF would increase significantly, which also validated the hazards of brittle damage [19].…”

Section: Effects Of Surface Defects On Initial Energy Deposition Of Kdp Crystalmentioning

confidence: 53%

Recent Advances in Laser-Induced Surface Damage of KH2PO4 Crystal

et al. 2020

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As a hard and brittle material, KDP crystal is easily damaged by the irradiation of laser in a laser-driven inertial confinement fusion device due to various factors, which will also affect the quality of subsequent incident laser. Thus, the mechanism of laser-induced damage is essentially helpful for increasing the laser-induced damage threshold and the value of optical crystal elements. The intrinsic damage mechanism of crystal materials under laser irradiation of different pulse duration is reviewed in detail. The process from the initiation to finalization of laser-induced damage has been divided into three stages (i.e., energy deposition, damage initiation, and damage forming) to ensure the understanding of laser-induced damage mechanism. It is clear that defects have a great impact on damage under short-pulse laser irradiation. The burst damage accounts for the majority of whole damage morphology, while the melting pit are more likely to appear under high-fluence laser. The three stages of damage are complementary and the multi-physics coupling technology needs to be fully applied to ensure the intuitive prediction of damage thresholds for various initial forms of KDP crystals. The improved laser-induced damage threshold prediction can provide support for improving the resistance of materials to various types of laser-induced damage.

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Section: Effects Of Surface Defects On Initial Energy Deposition Of Kdp Crystalmentioning

confidence: 53%

Recent Advances in Laser-Induced Surface Damage of KH2PO4 Crystal

et al. 2020

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“…The focal distance of the focusing lens used in this work was 2 m and the equivalent laser spot size was 280 μm. More experimental details on the employed instruments and the used parameters can be found in Refs [11,14]. Because the essence of light is an electromagnetic wave, the process of laser irradiation can be considered as the propagation of an electromagnetic wave through micro-milled KDP optics, which conforms to theory of wave optics.…”

Section: Test Of the Optical Performance Of Micro-milled Kdp Opticsmentioning

confidence: 99%

“…After comparing the outcomes of above methods, it is accepted that micro-milling is the most promising method to complete repair work and can be applied in the future engineering mitigation of laser damage growth on largeaperture KDP optics [10,12]. Nevertheless, it is not a simple and readily available task to remove micro-defects effectively and then curb the damage growth of KDP optics because there are many factors having great influences on the repairing results, including the targeted design of repair contours [13,14], the ductile-regime cutting of KDP brittle crystal [15][16][17], the optimization of process parameters [18,19], etc.…”

Section: Introductionmentioning

confidence: 99%

“…In recent years, research interest on the micro-milling of micro-defects on optical surface has mainly divided into two respects. One is to investigate how to design suitable repair contours for different types of defects on the promise of ensuring the minimum material removal [13,14]. For instance, the centrosymmetric contours like Gaussian contours are supposed to take place of the defect sites with circle shapes like homogeneously melted damage, while the elongated contours like Ellipsoidal contours ought to replace the defect sites with large length-width ratios like radial cracks and surface scratches [20].…”

Section: Introductionmentioning

confidence: 99%

“…But little work has been reported to investigate the influence of machined surface topography on the optical performance of optics under the environment of high laser irradiation. In actual repairing process, a micro ball-end milling cutter is used to sweep the micrometer-sized defects or damaged sites away along a given machining paths, and convert them into predesigned contours which are normally about 1mm width and tens of micrometers depth in size [14]. When the cutter moves along adjacent paths, periodic tool marks are unavoidable to be left on the machined surface owing to the spherical geometry of the cutter [27].…”

Section: Introductionmentioning

confidence: 99%

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Incident laser modulation by tool marks on micro-milled KDP crystal surface: Numerical simulation and experimental verification

Liu

Cheng

Liao

et al. 2019

Optics & Laser Technology

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Micro-milling has been accepted as the most promising method to repair the microdefects on the surface of KH2PO4 (KDP) optics. However, surface tool marks are inevitably introduced during the micro-milling repairing process, and could possess great potential risks in lowering the laser-induced damage threshold of KDP optics. The primary cause of laser damage growth of nonlinear crystals has been considered as its internal light intensification. In this work, how the tool marks impact the incident laser modulation as well as the laser-induced damage resistance of micro-milled KDP optics was theoretically and experimentally investigated. The results indicate that periodic tool marks can cause diffraction effect and result in significant relative light intensity modulation (IRmax), up to 5.6 times higher than that inside smooth crystal surfaces.Although the change trends of IRmax with respect to tool marks on both surfaces of KDP optics are similar, the IRmax induced by the rear-surface tool marks is nearly twice higher than that induced by the front-surface tool marks, which means the rear surface with tool marks are more vulnerable to be damaged. The period of tool marks determines the modulation degree and distribution patterns of light intensity inside KDP crystal while the residual height of tool marks can only slightly regulate the modulation degree of light intensity. The tool marks with a period of 1 μm normally give rise to serious light intensification and should be strictly excluded, while the period of tool marks from 10 μm to 20 μm is conducive to the laser damage resistance of micro-milled KDP optics, which were verified by the tests of transmittance capacity and laser damage resistance, and is supposed to be preferred in the actual repairing process of full-aperture KDP optics.

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