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We describe the design, fabrication and performance of an optimized one-dimensional subwavelength grating for use in 1064 nm wavelength laser systems. The laser-induced damage threshold (LIDT) under the irradiation of 12 ns 1064 nm pulses on the grating was performed, and a higher LIDT was obtained compared with LIDT of traditional antireflective coatings. Laser irradiation produces some morphological modifications on grating. Light interferometric surface profiler, scanning electron microscope and atomic force microscope were used to study these modifications, and these studies indicate the significant ablation and resolidification have occurred. To understand possible damage mechanisms, the role of electric field distribution inside the grating during the laser radiation process was investigated by a three-dimensional finite difference time-domain method, and the simulation result indicates the temperature distribution resulting from the internal electric field may be the main factor behind the damage. [ABSTRACT FROM AUTHOR]

[Display omitted] • First studied on the properties of mixture coating for picosecond laser applications. • Systematically studied the influence of Al 2 O 3 doping and annealing on the properties of HfO 2 -Al 2 O 3 mixture coating. • The properties of the mixture coatings may be improved by increasing the doped Al 2 O 3 content and annealing treatment. • Provide significantly support for the preparation of reflective coatings with a higher picosecond damage threshold. HfO 2 -Al 2 O 3 mixture coatings with different Al 2 O 3 doping contents are deposited on fused silica substrate using an electron-beam co-evaporation process. The effects of the material composition and thermal annealing temperature on the chemical states, crystal structure, transmittance spectra, refractive index, optical band gap, and picosecond laser-induced damage threshold (LIDT) properties of these HfO 2 -Al 2 O 3 mixture coatings are investigated. Characterization measurements confirmed that the properties of the mixture coatings may be improved by increasing the doped Al 2 O 3 content and thermal annealing. The experimental results show that, firstly, with the increase of the doped Al 2 O 3 content, the optical band gap and the LIDTs of the HfO 2 -Al 2 O 3 mixture coating increase monotonically. Secondly, the highest LIDT of 7.1 J/cm2 is obtained at an annealing temperature of 500 °C, which is ∼ 20 % higher than that of the as-deposited coating. The S-M 2 coating annealed at 500 ℃ shows a similar LIDT and a higher refractive index as compared to the pure Al 2 O 3 , which provides significantly support for the preparation of reflective coatings with a higher picosecond damage threshold. [ABSTRACT FROM AUTHOR]

Abstract: Antireflective sub-wavelength structures with high laser-induced damage threshold on fused silica are fabricated using a self-assembly technique, in which a porous yttrium oxide film is deposited as a mask followed by alkaline etching. By controlling the etching time, several sub-wavelength structures with different height, density and diameter have been made. The best reflectance is less than 2.87% for wavelengths from 300 to 1000nm after 1.5h etching. The laser-induced damage threshold of the etched glass measured by a 10ns Nd:YAG laser at a wavelength of 532nm was as high as 30J/cm2 compared to 16J/cm2 of blank glass. The specular reflectance of structures matches the theoretical simulation using a thin-film multilayer model, and the results reveal that the shape of the structures is similar to the calculated parabolic shape. Achieving antireflective sub-wavelength structures on fused silica paves the way for applications in laser systems. [Copyright &y& Elsevier]

The high optical performance and laser-induced damage threshold (LIDT) of broadband hafnium oxide/silica (HfO 2 /SiO 2) dichroic coatings with high transmittance and reflectance around 532 and 1064 nm, respectively, are essential for the efficiency of a harmonic separation system. However, the transmittance of dichroic coatings tends to drop rapidly at 532 nm because of the half-wave hole effect. Moreover, an intense electric field penetrates the coating (~6 μm thick) to the substrate, thereby generating a challenge to improve the LIDT at 532 nm. In this paper, we study the methods to improve the optical performance and LIDT of HfO 2 /SiO 2 dichroic coatings prepared by electron-beam evaporation. The inhomogeneity in the growth characteristics of the HfO 2 layer is studied and considered in the design of dichroic coatings, which can improve spectral performance, especially by broadening the transmittance bandwidth around 532 nm. Additionally, the effects of the different treatment procedures, including ultrasonic cleaning, acid-solution etching, and argon-ion-beam etching, of the fused silica substrate on the LIDT of dichroic coatings are investigated by the raster-scan damage test method. We observe that the LIDT of dichroic coatings at 532 nm is limited by the surface and subsurface defects of the substrate. Etching ~200 nm of the surface of the fused silica substrate can effectively inhibit the occurrence of low-energy catastrophic growth damage. Compared with acid-solution etching, argon-ion-beam etching can yield improved substrate surface quality and increased LIDTs of dichroic coatings at 532 nm. • The refractive index inhomogeneity of the HfO 2 single layer is consistent with that of the HfO 2 layer in dichroic coatings. • HfO 2 /SiO 2 dichroic coatings considering the refractive-index inhomogeneity of HfO 2 layer inhibit the half-wave hole effect. • Laser damage at 532 nm mainly originates from the substrate subsurface defects in the redeposition (Beilby) layer. • Argon-ion-beam etching can bring better substrate surface quality and higher LIDTs of dichroic coatings at 532 nm. [ABSTRACT FROM AUTHOR]

Antireflection (AR) coatings are deposited on UV grade fused silica substrates, which are cleaned in the dual ion beam sputtering device. Compared to ultrasonic and acid etching cleaning progress, ion beam etching improves the laser-induced damage threshold (LIDT) of substrates and AR coatings significantly at 355 nm. Ion beam etching declines the low LIDT defects drastically and removes lots of the impurity elements (Ce, Fe, K, and Na). Roughness test shows that the AR coatings and substrates with ion beam etching are very flat and of low roughness. Ion beam etching reduces the density of deep defect from substrates greatly. Damage morphologies show double layers delamination, which is explained via calculation of layer stress. This study will be helpful for preparation of high LIDT optical coatings. • The LIDT of the 355 nm AR coatings and substrates are improved greatly with ion beam etching of substrates. • The damage curves show that ion beam etching declined the low LIDT defects drastically. • The impurity elements (Ce, Fe, K, and Na) are removed efficiently, and the surfaces are quite smooth. • Damage morphologies show two different defects in AR coatings and correspond to the laser damage curves. • Laser damage mechanism of AR coatings is explained. [ABSTRACT FROM AUTHOR]