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Highlights: [•] The peeling-off damages occurred at the InterfaceHfO2→SiO2 or InterfaceTa2O5→SiO2. [•] The interface microstructure was not a major factor for peeling-off damages. [•] Incomplete oxides and Na, K, and Li ions should be the cause of stripping damage. [ABSTRACT FROM AUTHOR]

Abstract: We present a monitoring strategy based on using two pieces of witness glass, which are brought to the measuring position in a specially chosen sequence, each witness glass is monitored by one single wavelength. To reduce the thickness error, some thick layers are divided into two layers and monitored by different witness glasses. Theoretical analysis and experimental results have demonstrated that the proposed monitoring strategy can achieve spectral performance close to the theoretical design. [Copyright &y& Elsevier]

• HfO 2 –SiO 2 mixture coatings with different proportions were investigated. • Admixing 10% or higher SiO 2 in the mixture coatings suppresses inhomogeneity of HfO 2. • Short-wave pass dichroic laser mirror coatings were prepared using mixture layers. • Using HfO 2 –SiO 2 mixture layers fundamentally solves the half-wave hole effect. • Using different mixture layers gets further optical improvement in the pass band. Hafnia/silica (HfO 2 /SiO 2) short-wavelength pass dichroic laser mirror (DLM) coatings are widely utilized in high-power laser systems. However, the half-wave hole effect resulting from the refractive index inhomogeneity of HfO 2 severely restricts the spectra and potential applications of these coatings. To address this issue, an investigation was conducted on HfO 2 –SiO 2 mixture coatings with different proportions, which were produced by electron beam co-evaporation. Compared to the inhomogeneous growth characteristics observed in pure HfO 2 coatings, the introduction of 10 % or higher SiO 2 admixing in HfO 2 –SiO 2 mixture coatings results in an amorphous structure characterized by excellent refractive index homogeneity and improved surface smoothness. Leveraging this, different DLM coatings with the objective of achieving high transmittance across the 400 to 900 nm range were designed and prepared, while ensuring high reflectance at 1064 nm. The incorporation of HfO 2 –SiO 2 mixture layers instead of pure HfO 2 layers in the mirror coatings led to a fundamental inhibition of the half-wave hole effect throughout the entire broad transmission band, resulting in a substantial improvement in the optical performance of the coatings. Moreover, by incorporating several types of HfO 2 –SiO 2 mixture layers with different proportions in the coating stacks, the transmittance of DLM coatings in the pass band can be further increased, and the transmission fluctuations at different wavelengths can be further compressed. Additionally, compared to traditional DLM coatings with HfO 2 layers, DLM coatings incorporating HfO 2 –SiO 2 mixture layers exhibit lower roughness, higher laser-induced damage threshold (LIDT) at 532 nm, and similar LIDT at 1064 nm. These results indicate a promising strategy for fabricating DLM coatings tailored for high-power laser systems. [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]

The knowledge of the optical properties of coating materials at high temperatures is important for understanding the dynamic process of high-power laser-material interactions. In this paper, the variations of refractive index and physical thickness of single layer coatings were studied by ellipsometric spectroscopy at different temperatures. From 23 °C to 320 °C, a decrease and then an increase of the refractive index of SiO 2 , and HfO 2 single layer was observed, while the thickness of these layers increased first and then decreased. The inflection points of different coating materials occurred at different temperatures. Water evaporation processes, densification and hydrophilicity of films were used to explain the temperature dependent properties of the dielectric coatings. Results of the variation of refractive index and thickness of single layer coatings at different temperatures in the vacuum proved the mentioned theory. Moreover, HfO 2 single layer shows better resistance to both temperature change and vacuum change, indicating that it is promising for high-reflective coatings in photoelectric devices. Besides, the formation of transient defects during high power laser irradiation was interpreted considering the optical properties variation with temperature. Three confusing and debated issues concerning laser-coating interaction are interpreted and explained. • Change of coatings' optical constants with temperature were studied. • Mechanism relies on water evaporation, film densification and hydrophilicity. • Three confusing issues concerning laser-coating interaction are interpreted. [ABSTRACT FROM AUTHOR]

Fig.1. (a) SEM images of the fabricated low-oscillation dispersion mirrors (LODM). The surface GLAD SiO 2 layer has an ultra-low refractive index of 1.09, which is used to reduce the partial reflection of the surface layer, thereby reducing the dispersion oscillation of the entire mirror. (b) electric field intensity(EFI) distribution of three mirrors. (c) multi-wavelength Dynamic EFI distribution of LODM. In Brief. The dispersion oscillation and damage threshold of a dispersion mirror (DM) are the key influencing factors for high-quality pulses and outputting high power density. The sculptured structure film prepared by the glance-angle deposition(GLAD) technique has a porous structure, and its shape and porosity can be adjusted. In this study, we fabricated a low-oscillation DM (LODM) with a high damage threshold through a sculptured structure layer. Although the static electric field intensity (EFI) inside the LODM is 8.5 times that of the Bragg mirror, their thresholds are still close. As laser damage is a dynamic process, EFI is redistributed in time. A new EFI analysis model, which combines the influence of action time and different frequency components is employed. As a result, the EFI transfer to deep due to sculptured layer is the root cause of high damage threshold. In the depth of the film, there is a time difference in the formation of EFI peaks of different frequencies, which causes the EFI in the depth of the film to cancel out. The dynamic effect of few-cycle laser pulses or attosecond pulses damage will be more common. It can elucidate the ultrafast laser damage behavior of film components. [Display omitted] • A low-oscillation dispersion mirror (LODM) with a high damage threshold is fabricated through a sculptured structure layer; • A new electric field analysis model including time component is established to analyze ultrafast laser damage; • Introducing the standing wave field peak of the multilayer into the depth of the film may be a good way to increase the damage threshold. The dispersion oscillation and damage threshold of a dispersive mirror (DM) are the key influencing factors for high-quality pulses and outputting high power density. Here, we studied the femtosecond damage behavior of low-oscillation DMs(LODM) with SiO 2 sculptured layer. The monochromatic standing wave field(SWF) distribution widely used in ultrafast laser damage analysis is sufficient in Bragg mirror. In more complex systems, the actual electric field intensity(typically smaller) will dynamically change due to the broad bandwidth and the time difference of pulse propagation. Time-domain dynamic electric field intensity displays that the spatio-temporal evolution of the pulse within the stacks averages the electric field intensity, especially the electric field in the deeper layers. The dynamic effect of few-cycle pulses or attosecond pulses damage will be more meaningful. The time-domain dynamic electric field model can elucidate the ultrafast laser damage behavior. Introducing the time-domain dynamic electric model into the merit function can help us design optical coatings with high damage thresholds. [ABSTRACT FROM AUTHOR]