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Effect of two-step post-treatment on optical properties, microstructure, and nanosecond laser damage threshold of HfO <sub/>2</sub> /TiO <sub/>2</sub> /SiO <sub/>2</sub> multilayer high reflection films
摘要： HfO2/TiO2/SiO2 periodic multilayer high reflection films deposited by an electron beam are post-treated by two-step post-treatment and thermal annealing post-treatment, respectively. The optical properties, microstructures, surface morphologies, and laser-induced damage threshold (LIDT) of the films are studied comparatively. The results show that the two-step post-treatment enhances the high reflection films’ density and reduces the film surface roughness and the defects of the film. The test results show that the LIDT of HfO2/TiO2/SiO2 high reflection films treated by two-step post-treatment reaches 32.8 J/cm2, which is 110.26% higher than that of the untreated film. Compared with the HfO2/TiO2/SiO2 high reflection films after thermal annealing post-treatment, the LIDT increased nearly 27.6% after two-step post-treatment. Two-step post-treatment of high reflection films can effectively remove the defects on the surface of the film, reduce the oxygen vacancies inside the film, and further increase the laser damage threshold of the high reflection films.
关键词： laser-induced damage threshold,HfO2/TiO2/SiO2,two-step post-treatment,thermal annealing,multilayer high reflection films
更新于2025-09-19 17:13:59
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The impact of nano-bubbles on the laser performance of hafnia films deposited by oxygen assisted ion beam sputtering method
摘要： Hafnia is a high refractive index material used in the manufacturing of dielectric coatings for next generation lasers. The formation of defects during deposition is the major barrier to realizing high laser-damage resistant coatings for future high energy density laser applications. Understanding the precursors responsible for laser-induced damage in hafnia is therefore critical. In this work, we investigate the mechanism of laser-induced damage in 90-nm thick hafnia films produced by an oxygen assisted dual ion beam sputtering (IBS) process. Under pulsed, nanosecond ultraviolet laser exposure (355 nm, 8 ns), the laser-induced damage onset is found to be strongly dependent on the amount of argon and excessive oxygen entrapped in the nanobubbles within the hafnia films. The presence of nanobubbles is revealed and confirmed by small angle X-ray scattering and scanning/transmission electron microscopy coupled with high-angle annular dark-field. The damage onset is stable initially but decreases as the energy of oxygen goes beyond 100 eV. The damage initiation is ascribed to a laser-induced plasma generation within the nanobubbles through multiphoton ionization. The results reveal that nanobubbles formed in the IBS produced coatings are a potent precursor. Although nanobubbles are commonly present in IBS films, their negative impact on laser damage resistance of hafnia films has not been previously recognized. Our findings provide a fundamental basis for the development of potential mitigation strategies required for the realization of laser damage resistant hafnia films.
关键词： laser-induced damage,multiphoton ionization,ion beam sputtering,hafnia,nanobubbles
更新于2025-09-16 10:30:52
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Near-Field-Induced Femtosecond Breakdown of Plasmonic Nanoparticles
摘要： We studied the evolution of femtosecond breakdown in lithographically produced plasmonic nanoparticles with increasing laser intensity. Localized plasmons were generated with 40-fs laser pulses with up to 1.4 × 1012 W/cm2 peak intensity. The damage morphology shows substantial variation with intensity, starting with the detachment of hot spots and stochastic nanoparticle removal. For higher intensities, we observe precise nanolithographic mapping of near-field distributions via ablation. The common feature of these phenomena is the central role played by the single plasmonic hot spot of the triangular nanoparticles used. We also derive a damage threshold value from stochastic damage trends on the arrays fostering the optimization of novel nanoarchitectures for nonlinear plasmonics.
关键词： Laser-induced damage threshold,Plasmonic nanoparticles,Plasmonics,Field enhancement mapping
更新于2025-09-12 10:27:22
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Correlation between defect absorption and nano-second laser-induced damage of HfO2/SiO2 based high reflective coatings at 1064?nm
摘要： The distribution of defect weak absorption and nanosecond pulse laser induced damage characteristics of HfO2/SiO2 multilayers were investigated. A combination of in-situ measurements of defect weak absorption distribution and laser induced damage threshold (LIDT) map was proposed, whereby the evolution of defect weak absorption and the laser induced damage morphology under laser irradiation was studied. During the laser irradiation, some nodular and scalded defects can be removed or passivated by the low flux laser, and the absorption of these defect types was reduced accordingly. Besides, catastrophic destruction defects with enhanced absorption after laser irradiation would develop into catastrophic damage. Further, two-dimensional scanning of the sample surface was used to study the relationship between defects weak absorption and the LIDT. The results indicated that the correlation of defects weak absorption intensity distribution and LIDT map depended on defect evaluation properties during the laser irradiation.
关键词： Nanosecond pulse laser,HfO2/SiO2 multilayers,High reflective coatings,Laser-induced damage,Defect absorption
更新于2025-09-11 14:15:04
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Investigation of parameters governing damage resistance of nematic liquid crystals for high-power or peak-intensity laser applications
摘要： We investigate the damage resistance of saturated and unsaturated liquid crystals (Lc’s) under a wide range of laser excitation conditions, including 1053-nm pulse durations between 600 fs and 1.5 ns and nanosecond pulse excitation at 351 nm and 532 nm. This study explores the relationship between the LC’s resistance to laser-induced breakdown (damage) and the electronic structure (π-electron delocalization) of the constituent molecules. the laser-induced damage threshold at all wavelengths and pulse durations was consistently higher in saturated materials than in their unsaturated counterparts. the wavelength’s dependence in the results suggests that the energy coupling process that leads to laser-induced breakdown is governed by the energy separation between the ground state and the first and second excited states, while the pulse duration’s dependence in the results reveals the important role of electron relaxation between the excited states. A qualitative description was developed to interpret the experimental observations.
关键词： laser-induced damage threshold,liquid crystals,saturated materials,unsaturated materials,π-electron delocalization
更新于2025-09-11 14:15:04
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A hydrophobic ultralow refractive-index silica coating towards double-layer broadband antireflective coating with exceptionally high vacuum stability and laser-induced damage threshold
摘要： We report the fabrication of nanoporous silica coatings with tunable refractive indices by a one-step base-catalyzed sol-gel process using tetraethoxysilane as the precursor, hexamethylisilazane as the modifier at ambient conditions. The advantages of the present method are inexpensive, etchant-free and without high temperature calcination treatment. Importantly, porosity of the coatings can be tunable by changing the monomer ratio of the starting solution, which makes them suitable for top layer of broadband AR coatings. The tri-wavelength broadband AR coating with the refractive indices of the bottom and top layers as 1.27 and 1.16 was achieved on a fused silica substrate, which possessed high transmittance of 99.6%, 98.0% and 99.3% at 351 nm, 527 nm and 1053 nm, respectively. Moreover, the double-layer coating showed significant stability, when tested with polydimethylsiloxane pollution in vacuum for a week. In addition, LIDT of the double-layer coating was up to ca. 19.0 J cm?2 at a 6.3 ns laser pulse of 351 nm wavelength. This double-layer AR coating possesses excellent broadband AR performance, high LIDT, and excellent vacuum stability, which can open a new avenue to explore applications in high-power laser systems.
关键词： Antireflective coating,Laser-induced damage threshold,High-power laser system,Sol-gel,Vacuum stability
更新于2025-09-04 15:30:14