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A semi-organic nonlinear optical material L-Arginine tetrafluoroborate (LAFB) was synthesized as single crystal using Slow Evaporation Technique. Various properties of this material were analyzed to make it suitable for NLO applications. The structural behavior of the material was determined by single crystal XRD and found that the crystal has orthorhombic structure and was synthesized with P212121 space group. The High-Resolution X-Ray Diffraction (HRXRD) study was conducted to determine the change in the lattice parameters resulting from strain, defects or by other means in LAFB material. The diffraction curve analysis show that the grown crystal consisted of interstitial type point defect. The Shock Damage Threshold (SDT) measures the stability of the compound against shock, the analysis exhibits that under Mach number 2.2 up to 10th shock no significant cracks were observed in the crystal but damage area of the crystal was increased. The mechanical behavior of the sample against highly intense laser was analyzed through Laser Damage Threshold (LDT). The calculated value of LDT was to be 0.75 GW/cm2 for 1 pulse per second whereas it decreased to 0.57 GW/cm2 for 10 pulse per second. To explore the mechanical properties of the material, Nano indentation was carried out, by which the values of H 0 = 1 3 1. 5 4 8 MPa and E 0 = 4. 3 8 7 6 9 GPa were obtained. [ABSTRACT FROM AUTHOR]

Since the discovery of lasers, high-quality nonlinear optical (NLO) single crystals have served as the foundation for the creation of novel, cutting-edge devices that meet societal demands. Modern optoelectronic applications such as telecommunication lasers, optical fibers, photodiodes, solar cells, etc. favor high-performance nonlinear optical single crystals with improved optical nonlinearity. Organic crystals are extensively explored for these applications because of their high NLO coefficient. This paper deals with the problems and advancements of organic nonlinear optical single crystals. Here, we review the growth and characterizations of various tosylate family crystals from the vast realm of organic single crystals and their potential applications in the field of optoelectronic devices. Various properties like linear and nonlinear optical, thermal, mechanical, and laser damage threshold values for these samples have been summarized. The attempts are made for highlighting how these tosylate (p-Toluenesulfonic acid based) family crystals can be realized into efficient optoelectronic devices by summarizing variously reported cut-off wavelengths and their wide transmission ranges. [ABSTRACT FROM AUTHOR]

Addressing the challenge of breaking rocks deep within the earth requires innovative solutions, and the pulsed laser technology has emerged as a promising noncontact alternative for rock breaking. We developed an automated experimental platform with robotic arms and a rock mechanics testing device to quantitatively study the impact of laser technology on rock breaking. Our investigation delved into the damage caused to rocks by different types of lasers, focusing on understanding their underlying damage mechanisms. Pulsed lasers, excluding thermal effects, reduced the red sandstone strength by 68.07%, with a decrease in peak tensile force by 30-33 N per 1000 pulses. Furthermore, we conducted detailed quantitative analyses to understand how laser power (P), irradiation duration, and output energy affeted rock damage. Increasing laser power or irradiation duration enhanced rock damage since this increased the laser output energy. For every 100.00 W power increase, the peak force decreased by 51.00-88.00 N, and for every 1000.00 ms duration increase, the peak force decreased by 34.00-42.00 N. Maintaining constant output energy while changing the laser power revealed a quadratic nonlinearity in peak force, aiding in determining optimal laser parameters. This study highlights the potential of laser technology for effective rock fracturing during deep earth exploration. The established experimental platform improves the accuracy and reliability of laser-induced rock breaking, offering insights for future advancements in this field. [ABSTRACT FROM AUTHOR]

Mid‐infrared chalcogenide glasses often suffer from a low laser damage threshold due to their weak bond energy and the presence of impurities, particularly at the specific wavelength of 2.94 µm, which is widely used in medical applications. In this paper, we first investigated the effect of the hydroxyl (OH⁻) peak absorption coefficient on the laser damage properties of As2S3 glasses. The surface temperature distribution of chalcogenide glasses under laser irradiation was also analyzed using the finite element method (FEM) and in‐situ heat monitoring. The results showed that the surface temperature of the glass increases exponentially with the rise in the absorption coefficient at the OH− peak position. Subsequently, Raman spectra analysis and average bond energy (ABE) theory were employed to compare five typical chalcogenide glasses without hydroxyl absorption, revealing the relationship between the laser damage threshold and the bond energies of the glass networks. Finally, an optimized glass composition of Ge25As10S65 was identified, possessing the highest laser damage threshold of 340.98 J/cm2, more than twice that of traditional As2S3. These findings provide essential glass host and data references for the future development of mid‐ and far‐infrared optical fibers and waveguide devices. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced polymer (CFRP), noted for its outstanding properties including high specific strength and superior fatigue resistance, is increasingly employed in aerospace and other demanding applications. This study investigates the interactions between CFRP composites and high-energy lasers (HEL), with continuous wave laser powers reaching up to 120 kW. A novel automated sample exchange system, operated by a robotic arm, minimizes human exposure while enabling a sequence of targeted laser tests. High-speed imaging captures the rapid expansion of a plume consisting of hot gases and dust particles during the experiment. The research significantly advances empirical models by systematically examining the relationship between laser power, perforation times, and ablation rates. It demonstrates scalable predictions for the effects of high-energy laser radiation. A detailed examination of the damaged samples, both visually and via micro-focused computed X-ray tomography, offers insights into heat distribution and ablation dynamics, highlighting the anisotropic thermal properties of CFRP. Compression after impact (CAI) tests further assess the residual strength of the irradiated samples, enhancing the understanding of CFRP's structural integrity post-irradiation. Collectively, these tests improve the knowledge of the thermal and mechanical behavior of CFRP under extreme irradiation conditions. The findings not only contribute to predictive modeling of CFRP's response to laser irradiation but enhance the scalability of these models to higher laser powers, providing robust tools for predicting material behavior in high-performance settings. [ABSTRACT FROM AUTHOR]

Silica sol-gel antireflection coatings are used in high-power lasers due to their excellent laser damage resistance. These coatings are prepared using silica nanoparticles, and flaws generated during the coating preparation process are considered one of the factors that can lead to laser damage. Ring-shape flaws of micrometer-size usually appear on the surface of silica sol-gel antireflection coating. The morphologies of these flaws were investigated through optical microscopy, contact-type surface profilometer and scanning electron microscope. The diameters of the ring-shape flaws are from several micrometers to tens of micrometers. It has been demonstrated that the ring-shape flaws are nodule-like structures containing closely packed silica nanoparticles. The quasi-in-situ laser damage tests of the coated samples show the ring-shape flaws have a low damage probability. The formation of ring-shape flaws on the silica sol-gel coating is related to the polydispersity of the colloidal silica nanoparticles. Through the analysis of the size distribution of silica nanoparticles, a mechanism for flaws formation is proposed. Highlights: Morphologies of the ring-shape flaws on the surface of silica sol-gel antireflection coating. Quasi-in-situ laser damage tests of the ring-shape flaws on the silica coating. Formation mechanism of the ring-shape flaws on the silica sol-gel coating. [ABSTRACT FROM AUTHOR]

When irradiated by high-power lasers, fused silica optical component can be ablated, which seriously affects their laser-conducing capability and service life. Numerical simulations have been applied to investigate the ablation process, laser-induced damage threshold (LIDT), and propagation loss of fused silica optical component. The depth of the ablation crater increases linearly with the duration of irradiation, while the rate of development in the width of the ablation crater gradually decreases. The LIDT of the front surface of the fused silica optical component will significantly decrease, while the propagation loss of the fused silica component will have a considerable increase when the front surface of fused silica is damaged under laser irradiation. The propagation loss and the LIDT of the fused silica’s front surface are 26.49, 21.19, 20.60, 16.83, and 16.41GW/cm2 and 0.41, 1.02, 2.24, 3.46, and 5.31dB, respectively, after 50, 100, 150, 200, and 250μs of ablation. This work provides novel opportunities for investigating the intrinsic mechanism of laser-induced damage to fused silica, and offers guidance for the future development of fused silica optical elements that are highly resistant to laser-induced damage. [ABSTRACT FROM AUTHOR]

In this paper, the fatigue damage degree of low-alloy structural steel is evaluated by using the attenuation characteristics of laser-induced surface acoustic wave (SAW) during propagation. Taking the typical structural steel material Q345 as an example, a cracks model of fatigue damage is established, and the finite element method is used to solve the model. The results showed that the attenuation coefficient of SAW can reflect the depth and density of fatigue cracks. The surface measurement experiments of specimens with stress cycles of 0, 50000, 100000, 150000, and 200,000 showed that with the increase of stress cycles, the attenuation coefficient of SAW increases as a whole, indicating that it is feasible to evaluate the fatigue damage degree based on the attenuation of SAW. A method of applying tensile stress to the material to improve the sensitivity of fatigue damage evaluation is proposed. The tensile stress is used to offset the horizontal amplitude of the SAW, keeping the fatigue cracks in an open state and increasing the attenuation coefficient of SAW. The attenuation coefficient measurement experiment shows that this method is feasible. [ABSTRACT FROM AUTHOR]

The easy destruction of most conventional materials by high-energy lasers is a great concern. Anti-laser coatings with ablative heat absorption capabilities are effective in preventing laser damage. However, their extremely low reflectivity implies a high energy absorption rate, which can result in rapid failure. In this study, silicone resin matrix composite coatings were designed and prepared by incorporating ceramic modification components to realize desired optical transformation characteristics. The modification effects on ZrC/SiC, ZrSi 2 , TiC/SiC, and TiSi 2 were specifically studied with a high-energy continuous-wave laser (1080 nm). The results showed that oxidation reactions during laser ablation play a significant role in phase change and optical transformation. The element analysis proved that the composition rapidly changed from carbide and silicide to oxide, leading to the formation of oxide layer with relatively high reflectivity in laser ablation region. In particularly, oxidation and ablation of ZrSi 2 facilitated the exposure, gathering, and sintering of ZrO 2 , which realized an increase in reflection from 6.2 % to 34.9 % during laser ablation (500 W/cm2, 60 s). The optical transformation characteristics were compared with the evolution of diffuse reflection intensity and its corresponding differential curve, which indicates that ZrSi 2 exhibited the best performance. [ABSTRACT FROM AUTHOR]

The VO2 and VO2 -SiO2 composite films were prepared by sol-gel method. The phase structure and transmittance of films were characterized by X-ray diffraction (XRD) and ultraviolet visible spectrophotometer. The results reveal that the prepared VO2 film is monoclinic phase (B), and the XRD patterns of VO2 -SiO2 composite film is similar to that of VO2 film. The optical transmittance of films have reached over 90% within the range of 450 nm to 800 nm. The laser induced damage threshold (LIDT) of VO2 -SiO2 composite film is 3. 9 J/cm2, which is 77. 3% higher than that of VO2 film. The difference in damage morphology between VO2 film and VO2 -SiO2 film were studied by FESEM and step analyzer. The VO2 film exhibits melt type damage, while the VO2 -SiO2 film exhibits melt type damage and stress damage. In addition, laser-induced damage models for different films were constructed and damage characteristics and underlying mechanisms were discussed. [ABSTRACT FROM AUTHOR]

The laser cladding technology has the advantages of a low dilution rate, green environmental protection, and a small heat-affected zone of the substrate. The laser cladding forming process on the surface of ductile iron needs to be realized by multi-track and multi-layer overlapping, which will produce repeated thermal cycle accumulation and lead to thermal fatigue, and it is of great significance to quantitatively reveal the thermal fatigue damage mechanism of the laser cladding process. In this study, a numerical model of the EN-GJS-600-3 single-track laser cladding IN625 process on ductile iron was established, revealing the multifield coupling transient evolution process during the laser cladding. A multitrack overlapping laser cladding model with different overlap ratios was established to investigate the influence of multitrack overlapping on the temperature, flow rate, stress, and fatigue of the laser cladding process. Calculations show that the temperature and stress of the molten pool gradually stabilize at 1860 °C and 351 MPa after 1 s of single-track cladding. The maximum temperatures are 2030 and 2050 °C, the maximum flow rate is 0.27 m/s, and the maximum stress is 335 MPa and 358 MPa during 1 s of cladding at 30 and 60% overlap ratios, respectively. These are caused by the cumulative effect of thermal cycling in laser cladding. Thermal damage is more diffuse at a 30 percent overlap ratio and more concentrated at a 60% overlap ratio. Finally, it is found that the morphology of the numerically calculated cladding layer agrees well with the experimental result, which verifies the validity of the model. [ABSTRACT FROM AUTHOR]

This study investigates failure mechanisms in a typical thermal barrier coating (TBC) system comprising an EB-PVD columnar top coat, an aluminide bond coat, and a Ni-based single crystal superalloy substrate, simulating gas turbine operating conditions using a burner rig. TBC degradation, initiated by interfacial defects from the LASAT method, was studied during thermal gradient cycling under fast and slow cooling. In-situ optical and infrared imaging, along with ex-situ SEM cross-sectional analysis, monitored failure mechanisms. The Laser Shock for Damage Monitoring (LASDAM) technique provided insights into gradient and cooling rate impacts on columnar TBC damage. Results showed significant effects of cooling rate on delamination and localized failure at blister sites, with LASDAM revealing significant overheating at damage sites. Analysis included full-field temperature and damage assessment, emphasizing blister-driven delamination under severe thermal gradients. Discussion focused on elastic stored energy effects, noting that fast cooling induced transient conditions where reversed temperature gradients increased damage, limiting TBC lifespan. • LASDAM demonstrates simplicity and effectiveness for burner rig conditions. • Multiple points within a given specimen are analyzed under different conditions. • Blister formation induces overheating in gradients configuration. • The damage rate is directly influenced by both cooling rate and thermal gradient. • The local maximum temperature is also considered in our study. [ABSTRACT FROM AUTHOR]

Laser damage in films under long-term high-temperature conditions is a significant concern for advancing laser applications. This study focused on HfO2 films prepared using the sol–gel method with HfCl4 as a precursor. It examined the effects of temperature on various properties of the films, including their optical properties, microstructure, surface morphology, absorption, and laser-induced damage threshold (LIDT). The prepared film demonstrated desirable characteristics at the high temperature of 423 K, such as high transmittance, low absorption, and high LIDT. As the duration of its high-temperature exposure increased, the LIDT of the films gradually decreased. An intriguing finding was that the film's LIDT exhibited an exponential decay pattern with prolonged heating time. This observation could be attributed to the power-law increase in defects on both the internal and surface areas of the film as the duration of high-temperature exposure lengthened. Moreover, even after a 15-day heating period at 423 K, the film maintained an LIDT of 12.9 J/cm2, indicating its potential applicability in practical high-temperature environments. This study provided a general pattern and a universal formula for understanding the laser damage of sol–gel films at high temperatures over time. Furthermore, it opened possibilities for future developments of laser films suitable for extreme environments. [ABSTRACT FROM AUTHOR]

The increasing utilization of transparent ceramics in laser systems, particularly the magnesium aluminate spinel (MgAl2O4) transparent ceramic, has positioned it as the primary candidate for high energy laser system exit windows. Nevertheless, the increased energy and power of laser output necessitate higher standards for the laser-induced damage threshold in transparent ceramics. Residual micropores within transparent ceramics pose a potential source of damage. In this study, we employed the post-annealing process to effectively modulate the density and size of micropores. We first established the relationship between the density and size of micropores and laser damage threshold, which described the damage morphology of transparent ceramic in detail. Subsequently, we developed a multi-physical field coupled kinetic model of laser damage in micropores, providing a quantitative analysis of how factors such as micropore size and density influence the damage morphology of transparent ceramic surfaces when subjected to laser irradiation. Using time-resolved pumping and probing technology, we conducted in situ detection of laser damage caused by micropores, enabling detailed examination of damage kinetic behavior. Ultimately, this study elucidated the physical mechanism behind micropore-induced transparent ceramic damage. This has significant implications for enhancing the anti-laser damage performance of transparent ceramics in high-intensity laser systems.

The damage threshold of an Au‐coated flat mirror, one of the reflective optics installed on the FEL‐2 beamline of the Dalian Coherent Light Source, China, upon far‐UV free‐electron laser irradiation is evaluated. The surface of the coating is characterized by profilometer and optical microscope. A theoretical approach of the phenomenon is also presented, by application of conventional single‐pulse damage threshold calculations, a one‐dimensional thermal diffusion model, as well as finite‐element analysis with ANSYS. [ABSTRACT FROM AUTHOR]

The preparation of cubic boron nitride (CBN) grinding tools using laser cladding has the advantages of strong bonding, short time consumption and customizable abrasive arrangement. In this paper, a two-step laser cladding method was used to prepare CBN abrasive blocks with the aim of reducing laser damage to CBN grits during the laser cladding process. The cross-sectional morphology of CBN abrasive blocks under different laser power conditions was characterized, and the relationship among laser power, preparation method, and forming quality of Cu–Sn–Ti/CBN cladding layer was investigated. Then, the microstructure at the Cu–Sn–Ti/CBN interface under different laser power conditions was characterized, and the main phase compositions at the Cu–Sn–Ti/CBN interface were analyzed. Finally, the grinding tests were carried out on CBN abrasive blocks. The results show that as the laser power increases from 250 W to 400 W, the fracture ratio of CBN grits increases dramatically from 4.3 % to 17.3 %. TiN, TiB 2 , and TiB compounds are all detected at the Cu–Sn–Ti/CBN interface under different laser power conditions. The mass loss of the TC4 wheel caused by the CBN abrasive block initially increases and then decreases as the laser power increases from 250 W to 400 W. The CBN abrasive block has the optimum material removal performance at the laser power of 300 W using two-step laser cladding. The results provide a theoretical basis for the preparation of high-performance CBN grinding tools using laser cladding. [ABSTRACT FROM AUTHOR]

Nd,Y:SrF2 crystal is considered a promising laser gain material in high-energy laser systems owing to its advantages of long emission lifetime, low nonlinear refractive index and high thermal conductivity. In this study, photothermal weak absorption and laser-induced damage at 1064 nm on the surface of NYSF crystals were characterized. Based on 3D damage morphologies of cracking and bending, thermoelastic effects were considered as the damage mechanism. By analyzing weak absorption values and laser-induced damage thresholds, the exponential-Chapman quantitative relationship between laser fluence and weak absorption was observed. Additionally, the relationship between the laser fluence and growth behavior of the damaged area was investigated, indicating that the damaged area grew exponentially with an increase in fluence, and the area damaged by a secondary laser pulse was one order of magnitude larger than the primary damaged area. [ABSTRACT FROM AUTHOR]

This study examined the growth of the laser-damage performance in optical components under the fourth harmonic of Nd:glass laser irradiation (263 nm). The damage-growth threshold of the optical component was relatively low under 263 nm laser irradiation compared to 351 nm irradiation, owing to the higher energy level of 4 ω photons, and depended on the material characteristics. The preliminary growth of laser damage in fused silica and CaF2 under 263 nm laser irradiation is reported in this article. The damage growth coefficients of these two materials were obtained by continuously irradiating the optical components using a 263 nm laser with a pulse width of τ = 5 ns. The damage growth threshold of fused silica is lower than that of CaF2 because of differences between the materials. The damage characteristics, including the damage morphology and bulk damage, were analyzed. [ABSTRACT FROM AUTHOR]

Reactive ion etching (RIE) with fluorocarbon plasma is a facile method to tracelessly remove the subsurface damage layer of fused silica but has the drawback of unsatisfactory improvement in laser damage resistance due to the induction of secondary defects. This work proposes to incorporate O2 into the CHF3/Ar feedstock of RIE to suppress the formation of secondary defects during the etching process. Experimental results confirm that both the chemical structural defects, such as oxygen-deficient center (ODC) and non-bridging oxygen hole center (NBOHC) defects, and the impurity element defects, such as fluorine, are significantly reduced with this method. Laser-induced damage resistance is consequently greatly improved, with the 0% probability damage threshold increasing by 121% compared to the originally polished sample and by 41% compared to the sample treated with conventional RIE. [ABSTRACT FROM AUTHOR]

In order to address the issue of thermal damage induced by laser processing of carbon fiber reinforced polymer (CFRP), researchers have conducted an optimization study of process parameters in the laser processing of CFRP. Their aim is to elucidate the relationship between process parameters and processing quality to minimize thermal damage. However, during laser processing, there exists a complex nonlinear relationship between process parameters and processing quality, making it challenging to establish high-precision predictive models, while the intrinsic connection between these two aspects remains incompletely revealed. In light of this, this study proposes utilization of machine learning techniques to explore the inherent relationship between process parameters and processing quality and establishes a 5-13-5 type back-propagation (BP) neural network predictive model. Subsequently, genetic algorithms are employed to optimize the weights and thresholds of the BP neural network, and the model is then subjected to validation. The results indicate that the BP neural network predictive model yields average errors of 5% for surface heat-affected zone (HAZ), 2.9% for groove width, 5.9% for cross-sectional HAZ, 1.8% for groove depth, and 4.5% for aspect ratio, demonstrating a relatively high level of accuracy but with notable fluctuations. The GA-BP model, when predicting the surface HAZ and the groove width, achieves errors of 4.5% and 2.7%, respectively, which are lower when compared to the BP model, indicating a higher predictive accuracy. The GA-BP model established in this study unveils the intrinsic connection between process parameters and processing quality, providing a novel means for an effective quality prediction in the processing of CFRP. [ABSTRACT FROM AUTHOR]

A computer model predicting thresholds for laser induced corneal injury was used to systematically analyze wavelength, pulse duration, and beam diameter dependencies for wavelengths between 1200 and 1500 nm, for the exposure duration regime of 10 μs to 100 s. The thresholds were compared with the maximum permissible exposure (MPE) values to protect the cornea as specified in ANSI Z136.1-2022, ICNIRP 2013, and IEC 60825-1:2014. In the wavelength range between 1200 and 1400 nm, the dominant hazard transitions from the retina to the cornea. Consequently, limits are needed to protect both the cornea and the retina. In the lower wavelength range, the retinal limits are more conservative, while in the higher wavelength range, the corneal limits are lower. Comparison with injury thresholds shows that ANSI MPEs include a large safety margin for all wavelengths. Due to the 7 mm aperture stop defined in IEC 60825-1, levels permitted by the Class 3B limit exceed the predicted injury thresholds for small beam diameters and wavelengths between approximately 1350 and 1400 nm. The Class 3B limit does not appear to be sufficiently protective for these conditions. For skin MPEs, the margin between corneal injury thresholds and MPEs decreases steadily for wavelengths approaching 1400 nm. However, normal eye movements can be expected to reduce the effective exposure so that skin MPEs may serve as adequate limits to protect the cornea for wavelengths less than 1400 nm until a specific limit to protect the cornea is promulgated by ICNIRP. [ABSTRACT FROM AUTHOR]

Nonlinear optical (NLO) crystals that can extend the frequency range of coherent light have significant applications in laser technology, semiconductor manufacturing, and lithography. Herein, two interesting NLO crystals, A2Pb3[H2N(CH2COO)2]3Cl5 (A = K, Rb), are rationally obtained. Their porous structures are constructed on [Pb3Cl5O6] clusters that possess large hyperpolarizability and polarizability anisotropy, and are arranged in a parallel manner. Remarkably, A2Pb3[H2N(CH2COO)2]3Cl5 (A = K, Rb) exhibits comprehensive NLO performance, including strong phase‐matching second‐harmonic generation (SHG) response, the widest bandgap among lead oxychloride NLO crystals, larger laser damage threshold than 127 MW cm−2, suitable birefringence of 0.11@1064 nm, high thermal stability, non‐deliquescence, as well as facile crystal growth. Theoretical calculations and structural analysis demonstrate that their strong SHG response is predominantly originated from the [Pb3Cl5O6] cluster. This study will provide a unique method for the discovery of new interesting NLO crystals in future. [ABSTRACT FROM AUTHOR]

A facile sol-gel procedure was employed to create refractive-index gradient SiO2 antireflective (AR) films. A monolayer film, characterized by the porous crosslinking framework, was fabricated with a designed volume ratio mixture both with colloidal silica suspension and soluble organic polysiloxane. The upper layer for the bilayer film was a hexamethylisilazane (HMDS) modified colloidal silica suspension, leading to the film surface transfer to hydrophobic. The strategic design of nanostructures in the bottom and upper layers resulted in a refractive-index gradient SiO2 film with enhanced AR properties. The bilayer film demonstrated a transmittance of 99.5% at 1064 nm, accompanied by a notable reduction in reflectivity. Moreover, the laser-induced damage threshold of the bilayer film was increased by 30%, rising to as high as 24.7 J/cm2. The SiO2 nanostructured film both showed a refractive-index gradient structure with excellent AR properties and exhibited good laser damage resistance. [ABSTRACT FROM AUTHOR]

The graded-refractive-index SiO2 antireflective (AR) films were prepared using the sol–gel method. A monolayer with a porous nanonetwork structure was designed as the mixed volume ratio of 70:30 between the alkali- and acid-catalyzed SiO2 sols. As the top layer, the hexamethylisilazane (HMDS) modified alkali catalyzed SiO2 sols induced SiO2 nanoparticles transforming from hydrophilic to hydrophobic nature. In comparison with the structures of monolayer and bilayer films, the AR properties and laser damage resistance were investigated in detail. By designing the nanostructures of the bottom and top layers, the graded- refractive-index SiO2 film was obtained, consequently enhancing the AR performance. In the bilayer film, the transmittance reached ∼ 98%@532 nm and 97%@1064 nm, respectively, corresponding to the obvious reduction of reflectivity. The assembly of the bilayer SiO2 film increased the laser-induced damage threshold by ∼ 30% from 25.3 J/cm2 (monolayer) to 33.1 J/cm2 (bilayer). The inducement of laser damage was further revealed by the analysis of morphological changes induced by laser damage, attributing to the initiator absorption of environmental contaminations. Therefore, the SiO2 film not only provided a graded-refractive-index structure with good AR performance, but also had high laser damage resistance. The unique graded-refractive-index structure of SiO2 AR films offers a new strategy for improving the performance of optical components in high-power laser systems. [ABSTRACT FROM AUTHOR]

The mechanism of the combined process of ion beam sputtering (IBS) and HF acid etching on the chemical structure defects of fused silica and its laser damage resistance performance were investigated in this paper. During the removal process of surface material, the sputtering effect causes lattice atoms to flee their native space locations, and a large amount of unsaturated chemical structures are produced on the silica surface, which improves the chemical activity of Si and O atoms, accelerates the chemical reaction process between surface atoms and water molecules, increases the content of hydroxyl groups (OH-) in the shallow layer, and enhances the photothermal weak absorption intensity. However, the increase in hydroxyl content weakens the binding strength of silicon–oxygen bonds, destroys the spatial network structure of silica bulk, and reduces its mechanical strength, resulting in a decrease in its laser damage resistance performance. The paper reveals for the first time the mechanism by which IBS changes the structure characteristics of silica material, accelerates the surface hydroxylation process, and thereby reduces the laser damage resistance performance. This work provides technical guidance for effectively suppressing chemical structure defects on silica surfaces and improving the laser damage resistance performance of optical components under high-flux laser irradiation. [ABSTRACT FROM AUTHOR]

Featured Application: Large scale laser operation. Complex laser use. The maximum energy at which a laser can be operated safely is a matter of paramount importance. This is patently related to laser induced damage. In the nanosecond regime, this poses a unique challenge, as it is not solely influenced by laser intensity or thermal load. Instead, it arises from the cumulative effects that includes those two factors. While extensive research has explored this dependence for various pulse lengths, the exploration of different longitudinal modes and temporal shapes is relatively limited. Our study aims to fill this gap by determining the safe operational fluence for any pulse shape, leveraging established dependencies on pulse duration. We propose a straightforward and adaptable method to ascertain these operational limits, independent of the type or origin of laser damage. This approach allows us to derive fluence limits for diverse pulse shapes. [ABSTRACT FROM AUTHOR]

Laser ablation damage has an important impact on the load-bearing capacity of the aircraft structure. This paper first uses ABAQUS ALE adaptive grid technology to establish and verify the numerical simulation analysis method of laser irradiation ablation of CFRP laminates. Then a finite element simulation analysis was conducted on the buckling process of the CFRP cylindrical shell under the combined loading conditions of laser irradiation and axial compression, and the critical buckling load and buckling mode of the cylindrical shell under different conditions were obtained. The effects of ablation damage and laser irradiation position on the critical buckling load are also discussed. When the laser irradiation position is between the end and the midpoint of the axis in the axial direction of the cylindrical, and is farthest from the axis in the radial direction, buckling failure is prone to occur. [ABSTRACT FROM AUTHOR]

The use of composite plate structures has become increasingly prevalent in industries such as civil engineering, aerospace, high-speed rail, automotive, and wind power. However, the propagation of ultrasonic Lamb waves in these structures is subject to multi-modal and frequency dispersion effects, which, coupled with the complicated anisotropic propagation mechanism of composite materials, makes it challenging to extract damage scatter signals without a health signal as a reference. In this study, we apply the frequency-wavenumber (f - k) domain filter wavefront modal method to carbon fiber reinforced polymer (CFRP) materials and use a three-dimensional (3D) window function to achieve different modalities and their corresponding damage reflection signals in the absence of a reference dispersion curve. Single modal damage imaging is achieved using a common source method (CSM) by laser vibration scanning experiment. To effectively extract single modalities in laminate material damage detection, a 3D filter window function was constructed. Considering the skew angle correction, it can effectively remove the direct wave signal, so as to realize the imaging of the damage. [ABSTRACT FROM AUTHOR]

KDP crystal is one of the most important parts in high-powered laser facilities, and the deformation control of KDP crystal has an important impact on the final laser frequency doubling efficiency. This paper proposes an assembly method based on small-hole gas suspending plate compressed gas-assisted support to accurately control the deformation of KDP crystals. First, the flow equation of gas flow through the small hole is derived, and the influencing factors of the bearing capacity of the overall gas flotation plate are further deduced. Secondly, the finite element model of the fluid-structure coupling is established to calculate the stress and deformation of the KDP crystal. Finally, the assembly process of the gas-suspending plate is optimized and the deformation control effect is verified based on the laser damage threshold experiment. The results show that the Pv value of the KDP crystal can be controlled at 11.17 nm by rationally designing the structural parameters of the small-hole gas-floating plate. The gas suspension into the frame is a reliable way to assemble KDP crystal. [ABSTRACT FROM AUTHOR]

As a wide band gap semiconductor, alkaline-earth metal sulfides (AES) with low phonon energy, high laser damage threshold, and high transmittance in infrared, have wide application prospects in bioimaging, spectral conversion, and solid-state lighting. However, AES nanocrystals (NCs) suffer from the weak chemical-stability and low mechanical-stability, and can be easily oxidized in humidity and oxygen. Incorporation of AES NCs into inorganic glass is expected to overcome those inherent limitations. In this work, a new type of oxysulfide glass-ceramics containing CaS, SrS, BaS, Sr x Ba 1−x S, and Ca x Sr 1−x S NCs is developed, and average diameters of these AES NCs are tuned in the range of 3–18 nm. Precipitation of AES NCs not only improves the mechanical properties of glass, but also maintains high transmittance (˃60%) in the spectral range of 1–4.3 µm. Results reported in this work offer a new pathway for developing novel oxysulfide glass-ceramics for multi-functional optical devices. [ABSTRACT FROM AUTHOR]

Sapphire optical components are prone to cracks and scratches during grinding, installation, and service, which affects the laser damage resistance. In order to improve the laser damage resistance of sapphire damaged surface, the influence of surface damage on the laser damage resistance was analyzed. The repair mechanism of wet etching on the damaged surface was expounded. The results show that the reduction of damage frequency and depth can reduce the LIMF, and the LIMF caused by ellipsoidal damage is less than prism damage. The texture direction relationship between the two surfaces influences the internal LIMF. Compared with the vertical surface damage, the parallel surface damage has a larger LIMF value. The LIMF value of the etching surface is minimal. The characteristics of the damaged surface before and after etching were compared. The results show that the surface damages are passivated and merged after etching, and the surface transforms into ellipsoidal features. These changes are conducive to improving the laser damage resistance. Finally, the effect of the etching process on surface quality is analyzed. The formation mechanism and etching repair mechanism of sapphire damaged surface at the atomic scale were revealed by molecular dynamics simulation. Finally, the laser damage resistance of sapphire surface was tested, and the feasibility of wet etching was verified. [ABSTRACT FROM AUTHOR]

Stimulated Brillouin scattering (SBS) is a potential risk for laser damage in the experiments carried out at the National Ignition Facility (NIF), and by altering the energy deposition pattern in hohlraums, it affects the symmetry of indirect-drive inertial confinement fusion implosions. We have surveyed backward SBS on outer-cone quads across NIF integrated hohlraums of various platforms numerically, using three-dimensional (3D) simulations with the backscatter code pF3D [Berger et al. Phys. Plasmas 5, 4337 (1998)] and ray-based gain calculations. Simulated reflected powers and energies, as well as the spectrum of reflected light all compare favorably with measurements. Ray-based calculations of exponential SBS amplification ("gain"), which assume a strongly damped plasma wave and steady-state response, are performed using a novel method that includes the 3D speckled field of the laser that drives SBS. This approach is useful for understanding qualitative differences between hohlraum designs and identifying regions susceptible to SBS within hohlraums. Quantitatively, gains are not found to correlate with SBS reflectivities in 3D, necessitating fully wave-based calculations that naturally include diffraction and various temporal dependencies. [ABSTRACT FROM AUTHOR]

The fabrication of SSD-free fused silica optics is a crucial objective for high-power laser applications. To treat the surface of polished fused silica, a combination of RIE/RIBE and deep-controlled etch (DCE) techniques are typically employed. Currently, it is important to consider and study the ideal etching depth and precision while using combined etching techniques to remove the identified SSD. Herein, we present a novel approach to identify the distribution of SSD in fused silica, which corresponds to a specific grinding/polishing process condition. Our method involves using a mobile RIBE to perform cone cutting and remove material from the polished fused silica surface. Afterward, we etch the optical element's surface with HF to visualize the subsurface cracks and understand their relationship with the RIBE depth. Through a systematic investigation of the combined etching technique, we establish a correlation between the depth of RIBE and DCE and the performance of laser damage. The combined etching technique can be implemented as a dependable approach to treat the surface/subsurface defects in fused silica and has the potential to improve laser damage resistance significantly. [ABSTRACT FROM AUTHOR]

Correlating damage outcomes to a retinal laser exposure is critical for diagnosis and choosing appropriate treatment modalities. Therefore, it is important to understand the causal relationships between laser parameters, such as wavelength, power density, and length of exposure, and any resulting injury. Differentiating photothermal from photochemical processes in an in vitro retinal model using cultured retinal pigment epithelial cells would be a first step in achieving this goal. The first-order rate constant of Arrhenius has been used for decades to approximate cellular thermal damage. A modification of this equation, called the damage integral (Ω), has been used extensively to predict the accumulation of laser damage from photothermal inactivation of critical cellular proteins. Damage from photochemical processes is less well studied and most models have not been verified because they require quantification of one or more uncharacterized chemical species. Additionally, few reports on photochemical damage report temperature history, measured or simulated. We used simulated threshold temperatures from a previous in vitro study to distinguish between photothermal and photochemical processes. Assuming purely photochemical processes also inactivate critical cellular proteins, we report the use of a photothermal Ω and a photochemical Ω that work in tandem to indicate overall damage accumulation. The combined damage integral (ΩCDI) applies a mathematical switch designed to describe photochemical damage relative to wavelength and rate of photon delivery. Although only tested in an in vitro model, this approach may transition to predict damage at the mammalian retina.

Laser anti-drone technology is entering the sequence of actual combat, and it is necessary to consider the vulnerability of typical functional parts of UAVs. Since the concept of ''vulnerability'' was proposed, a variety of analysis programs for battlefield targets to traditional weapons have been developed, but a comprehensive assessment methodology for targets’ vulnerability to laser is still missing. Based on the shotline method, this paper proposes a method that equates laser beam to shotline array, an efficient vulnerability analysis program of target to laser is established by this method, and the program includes the circuit board and the wire into the vulnerability analysis category, which improves the precision of the vulnerability analysis. Taking the UAV engine part as the target of vulnerability analysis, combine with the ''life-death unit method'' to calculate the laser penetration rate of various materials of the UAV, and the influence of laser weapon system parameters and striking orientation on the killing probability is quantified after introducing the penetration rate into the vulnerability analysis program. The quantitative analysis method proposed in this paper has certain general expansibility, which can provide a fresh idea for the vulnerability analysis of other targets to laser.

Laser damage in films under long-term high-temperature conditions is a significant concern for advancing laser applications. This study focused on HfO2 films prepared using the sol–gel method with HfCl4 as a precursor. It examined the effects of temperature on various properties of the films, including their optical properties, microstructure, surface morphology, absorption, and laser-induced damage threshold (LIDT). The prepared film demonstrated desirable characteristics at the high temperature of 423 K, such as high transmittance, low absorption, and high LIDT. As the duration of its high-temperature exposure increased, the LIDT of the films gradually decreased. An intriguing finding was that the film’s LIDT exhibited an exponential decay pattern with prolonged heating time. This observation could be attributed to the power-law increase in defects on both the internal and surface areas of the film as the duration of high-temperature exposure lengthened. Moreover, even after a 15-day heating period at 423 K, the film maintained an LIDT of 12.9 J/cm2, indicating its potential applicability in practical high-temperature environments. This study provided a general pattern and a universal formula for understanding the laser damage of sol–gel films at high temperatures over time. Furthermore, it opened possibilities for future developments of laser films suitable for extreme environments.

Phase matching is indispensable for high efficiency of second‐order nonlinear optical (NLO) crystals. Thousands of these crystals rely on birefringence phase matching, whereas only a few of them are quasi‐phase matching without the restriction of birefringence. Herein, using oriented seeds inch‐sized LiNH4SO4 (LAS) single crystals are successfully grown. LAS is NLO‐active with a very short deep‐UV absorption edge of 171 nm and high laser damage threshold up to 1.47 GW cm−2 at 1064 nm, 10 ns, but its birefringence is merely 0.0078@532 nm, which is too small to realize birefringence phase matching in deep‐UV region. Fortunately, P−E hysteresis loop, variable‐temperature NLO tests, and ferroelectric domain observations confirm that LAS is ferroelectric. Furthermore, LAS exhibits small refractive index dispersion resulting in a relatively long periodic length of 1.4 µm and its single domain structure can be easily obtained by electrical poling. These attributes make LAS a scarce NLO candidate for deep‐UV quasi‐phase matching. This work highlights the longly overlooked potential of sulfates and provides new opportunities for deep‐UV NLO materials. [ABSTRACT FROM AUTHOR]

Nonlinear optical properties play a key role in technologies such as broadband laser light sources and ultrafast laser machining. With the emergence of transparent nanocrystalline Al2O3 ceramics as an alternative to single crystal alumina (sapphire), it is critical to understand their nonlinear optical behavior. Here, we report the demonstration of supercontinuum generation in polycrystalline alumina ceramics. Substantial broadening was observed when a focused 515 nm pulsed (260 fs) laser propagated through the ceramic sample. The broadening increased with increasing laser power and displayed stokes/anti-stokes asymmetries. At higher incident power, permanent damage was observed. Our results show that transparent nanocrystalline Al2O3 ceramics have a higher material removal rate than single crystal alumina. These results have interesting implications for laser machining as well as integrated photonics. [ABSTRACT FROM AUTHOR]

Most traditional 2D materials have small bandgaps, resulting in low laser damage thresholds and limiting their applications in the ultraviolet region. Recently experimentally synthesized 2D GaN and ZnO can be such candidates due to their wide bandgaps, high charge mobilities, and optical transparency. Here, the van der Waals heterostructure GaN/ZnO is predicted that can exhibit both wide bandgap and strong second harmonic generation (SHG) response by compelling simulations. The results show the heterostructure always exhibits type‐II band alignment under all probable stacking configurations. The out‐of‐plane SHG coefficients are up to 90 pm V−1 at 400 nm, comparable to those of MoS2 and MoSe2 and higher than most 3D crystals. Interestingly, the positions are enhanced with localized, symmetric, and stacking‐dependent features in the Brillouin zone. This peculiar momentum space behavior is originated from the relative strength of two distinct mechanisms contributing to the second‐order nonlinear optical (NLO) response, that is, a purely interband transition part and a mixed interband‐intraband contribution. Thus, this study proposes that GaN/ZnO heterostructure may be an efficient and high laser damage thresholds (LDTs) NLO material and an interesting platform for studying NLO optical properties. [ABSTRACT FROM AUTHOR]

In the pursuit of mitigating or eradicating thermal damage defects during laser processing of carbon fiber-reinforced polymers (CFRP), the application of picosecond lasers with ultra-short pulse durations has emerged as a promising approach. Despite the adoption of picosecond lasers, the occurrence of thermal damage defects in CFRP processing persists. As a result, a more comprehensive comprehension of the mechanisms behind thermal damage formation and material removal in picosecond laser processing of CFRP is imperative. This study utilizes a picosecond laser at a wavelength of 532 nm to scribe the surface of braided CFRP. The focus is primarily on analyzing the mechanisms of thermal damage formation and material removal. Specifically, the effects of single-pulse energy density, line energy, and number of pulses in the spot range controlled by the process parameters on thermal damage and dimensional characteristics of the groove are evaluated. The results indicate that ablation, combustion and mechanical effects are the main forms of CFRP removal. Simultaneously, the groove also presents typical thermal damage defects as carbon fiber pull-out, heat-affected zone (HAZ), cracks, etc.. Furthermore, this study introduces a pioneering theoretical analysis of the effects of process parameter variations on effective thermal efficiency and the evolution of surface HAZ. This study contributes to the enhancement of the control capabilities against thermal damage in picosecond laser processing of CFRP, offering a crucial theoretical framework for further advancements in this domain. [ABSTRACT FROM AUTHOR]

Surface defects which are caused by diamond fly-cutting can degrade the optical characteristics of KDP crystals by inducing the laser damage and resultantly shortening the service life when working in the condition of extremely high-power laser irradiations. The ball-end milling repair can totally remove the defects and correspondingly enhance the ability of the KDP crystals to resist laser damage. However, because of the existence of pull-milling, push-milling, down-milling, and up-milling in the complex machining trajectory, it is of great challenge for soft-brittle KDP crystals to achieve full plastic domain milling of repair points for obtaining ultra-smooth repaired surface. In this study, theoretical models of the maximum uncut chip thickness (UCT) considering the defect are constructed in the various milling modes. The cutting force and surface morphology affected by milling modes on the defective surface are simulated using a three-dimensional (3D) finite element model. Combined with the simulations, micro-milling tests are employed to confirm the influence of milling modes on the material removal mechanisms for defective KDP crystals by cutting force, surface morphology, surface roughness and specific cutting energy (SCE). It is found that defects could reduce the maximum UCT to distinct degrees in the various milling modes. Defects have a greater influence on the maximum UCT in the push-milling mode than that in the pull-milling mode, while the influence is the same in the up-milling and down-milling modes. Interestingly, the ductile removal mode occurs on the both defect-free and defective surfaces in the pull-milling mode when the feed per tooth (f z) is 0.5 µm/z. In contrast, the brittle-ductile transition caused by surface defects occurs in the other three milling modes. Furthermore, defects would lead to severer size effect in the all milling modes. When the f z is 0.1 µm/z, for the defective surface, the SCE is larger and the ploughing effect is more significant in the push-milling mode compared to the pull-milling mode. More importantly, as a result of the difficulty of chip discharge, the SCE is greater in the up-milling mode than in the down-milling mode on the defective surface. This work reveals the influence mechanism of milling modes on the material removal process for defective KDP crystals and offers a theoretical foundation and technical value for improving the repaired surface quality of functional KDP crystals served as the optical devices. [Display omitted] • Effect of milling modes on cutting mechanisms of defective KDP crystal was explored. • The models of maximum uncut chip thickness considering defects were established. • Surface defects could cause the brittle-ductile transition and severe size effect. • Pull-milling was the easiest to obtain ultra-smooth surface of defective KDP crystal. [ABSTRACT FROM AUTHOR]

The photoexcited structural changes by the femtosecond laser pulses is one of the basic principles for laser processing techniques such as cutting and slicing. The femtosecond laser pulses photoexcite various structural changes of defects and nanovoids in MgO single crystals, and then such deficiencies develop into cracks. However, the precise roles of laser polarization during this process are unknown. Here we show that the photoinduced defects and nanovoids were formed along the <100> direction corresponding to the slip plane. Remarkably, the distribution of defects and nanovoids in [100] and [010] directions changed according to the polarization direction, resulting in polarization-dependent birefringence. Furthermore, depending on the pulse energy, the laser damage along the scanning direction was observed in the lower part of the focal region due to multiple filamentations. [ABSTRACT FROM AUTHOR]

The application range of fused silica optical components can be expanded and the cost of fused silica components can be reduced by depositing the same material film on fused silica substrate. However, due to the different manufacturing process, the performance of ALD SiO2 film is lower than that of fused silica substrate, which also limits the use of this process. In this paper, ALD SiO2 film with different thicknesses were deposited, and then the structure and properties were tested. Finally, the ALD SiO2 film was treated via the annealing process. Transmission electron microscopy (TEM) showed that the ALD SiO2 film had good compactness and substrate adhesion. The Raman spectra showed that the ALD SiO2 film and substrate had the same structure, with only slight differences. The XRD pattern showed that ALD-fused silica did not crystallize before or after annealing. The infrared spectra showed that there was an obvious Si-OH defect in the ALD SiO2 film. The laser damage showed that the ALD SiO2 film had a much lower damage threshold than the fused silica substrate. The nanoindentation showed that the mechanical properties of the ALD SiO2 film were much lower than those of the fused silica substrate. After a low-temperature annealing treatment, the ALD SiO2 film Si-OH defect was reduced, the ALD SiO2 film four-member ring content was increased, the elastic modulus of the ALD SiO2 film was increased from 45.025 GPa to 68.025 GPa, the hardness was increased from 5.240 GPa to 9.528 GPa, and the ALD SiO2 film damage threshold was decreased from 5.5 J/cm2 to 1.3 J/cm2. [ABSTRACT FROM AUTHOR]

Micro surface defects (SDs) would be unavoidably induced on most fused silica surfaces (FSSs), substantially reducing their laser-induced damage thresholds (LIDTs). There is still no clear understanding of the relation between SD structural feature and their LIDTs, which poses a challenge to the recognition and mitigation of the dangerous SDs with low LIDTs in industrial production. In this work, the brittle-plasticity and stress states of the SDs are found to dominate the atomic point-defect densities on FSSs and resultantly dominate their LIDTs for the first time. Based on this, the SDs have been divided into four categories: pressure-induced brittle defects (PBDs), pressure-induced plastic defects (PPDs), tension-induced brittle defects (TBDs) and tension-induced plastic defects (TPDs). Based on the tested LIDTs, laser damage morphologies and photoluminescence (PL) characteristics, the laser damage resistance of different kinds of SDs are compared, whose reasons are revealed on the basis of the molecular dynamics (MD) simulations. The sharp increase of the atomic point-defect density from the plasticity to the brittleness of the material, the significant disparity in tensile and compressive strength of fused silica, the distinctly different material response behaviours under tensile and compressive forces, as well as the opposite effects of the tensile and compressive forces on the material compactness significantly affect the atomic point-defect densities on FSSs and resultantly contribute to the different laser damage resistance of different kinds of SDs. This work possesses great significance in solving the laser damage on FSSs. It could also provide a new understanding of the impact of the tensile and compressive forces on the LIDTs of various optical elements. [ABSTRACT FROM AUTHOR]

Detecting subsurface defects in optical components has always been challenging. This study utilizes laser scattering and photothermal weak absorption techniques to detect surface and subsurface nano-damage precursors of single-crystal silicon components. Based on laser scattering and photothermal weak absorption techniques, we successfully establish the relationship between damage precursors and laser damage resistance. The photothermal absorption level is used as an important parameter to measure the damage resistance threshold of optical elements. Single-crystal silicon elements are processed and post-processed optimally. This research employs dry etching and wet etching techniques to effectively eliminate damage precursors from optical components. Additionally, detection techniques are utilized to comprehensively characterize these components, resulting in the successful identification of optimal damage precursor removal methods for various polishing types of single-crystal silicon components. Consequently, this method efficiently enhances the damage thresholds of optical components. [ABSTRACT FROM AUTHOR]

Zinc germanium phosphide (ZGP) crystals have garnered significant attention for their nonlinear properties, making them good candidates for powerful mid-IR optical parametric oscillators and second-harmonic generators. A ZnGeP2 single crystal was treated by deep magnetorheological processing (MRP) until an Angstrom level of roughness. The studies presented in this article are devoted to the experimental evaluation of the influence of deep removal (up to 150 μm) from the surface of a ZnGeP2 single crystal by magnetorheological polishing on the parameters of optical breakdown. It was shown that the dependence of the ZnGeP2 laser-induced damage threshold on MRP depth is a smooth monotonically decreasing logarithmic function. The obtained logarithmic dependence indicates the thermal nature of optical breakdown and the dependence of the ZnGeP2 laser-induced damage threshold on the concentration of surface absorbing defects. [ABSTRACT FROM AUTHOR]