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In this study, four Ta 2 O 5 -based mixture coatings, including Ta 2 O 5 -TiO 2 , Ta 2 O 5 -HfO 2 , Ta 2 O 5 -Al 2 O 3 , and Ta 2 O 5 -SiO 2 , are deposited via plasma-ion-assisted electron-beam co-evaporation and compared with a Ta 2 O 5 monolayer coating. The chemical compositions, microstructures, and optical and femtosecond laser-induced damage threshold (LIDT) properties of the coatings are investigated. For different doping materials, when the refractive indices of the mixture coatings are close, the femtosecond LIDTs exhibit a considerable difference. The experimental results indicate that the Ta 2 O 5 -HfO 2 mixture coating exhibits a larger optical bandgap and higher femtosecond LIDT than other coatings. The 1-on-1 LIDT of the Ta 2 O 5 -HfO 2 mixture coating is approximately 1032.3 mJ/cm2 (170 fs), which is 25% higher than that of the Ta 2 O 5 monolayer coating. We believe the Ta 2 O 5 -HfO 2 mixture will be useful for various multilayer coatings such as chirped mirrors and other mirrors in femtosecond laser applications. • The effect of doping materials on Ta 2 O 5 -X mixtures is systematically studied. • Ta 2 O 5 -X mixtures with similar refractive indices show different optical bandgaps. • The optical bandgap affects the femtosecond laser-induced damage threshold. • The Ta 2 O 5 –HfO 2 mixture coating exhibits excellent performance. [ABSTRACT FROM AUTHOR]

HfO 2 monolayer coatings are grown by plasma-enhanced atomic layer deposition (PEALD), and the effects of the thermal annealing atmosphere and temperature on the surface morphology, crystal structure, chemical composition, optical absorption, and laser-induced damage threshold (LIDT) of the HfO 2 monolayer coatings are investigated. The experimental results show that annealing in an oxygen atmosphere is more beneficial to the decomposition of impurity compounds (carbonates and amines) and the elimination of oxygen deficiency in HfO 2 coating than in a nitrogen atmosphere. Compared to the as-deposited coating, the HfO 2 coating annealed under an oxygen atmosphere and specific temperature has lower C and N impurity contents, a better stoichiometric ratio, and thus lower absorption and higher LIDT. The highest LIDT (at 355 nm) of 6.3 J/cm2 is obtained at an annealing temperature of 700 ℃, which is approximately three times that of the as-deposited coating. We believe that this experimental result can help improve the LIDT of PEALD-grown oxide coatings or other oxide coatings containing similar impurities. • The effect of annealing on the properties of PEALD HfO 2 coatings is investigated. • The carbonates and amines in the HfO 2 coating decompose during annealing. • The oxygen-annealed HfO 2 coating has lower absorption and higher LIDT. • The oxygen-annealed HfO 2 coating shows different damage morphology. [ABSTRACT FROM AUTHOR]

Plate laser beam splitter (PLBS) coatings for intensity-splitting in high-power laser applications face increasing requirements, where the challenge is to simultaneously satisfy a given transmittance (T)/reflectivity (R) intensity-splitting ratio with a certain bandwidth, and a high laser damage threshold (LIDT). Traditionally, a given T/R ratio is achieved by using a non-quarter-wave design. We propose a quarter-wave design strategy for arbitrary T/R ratios by using mixture layers with tunable refractive index (n) and optical bandgap as high- n layers. Two quarter-wave PLBS coatings based on HfO 2 –Al 2 O 3 mixture with a designed T/R ratio of 50:50 are experimentally demonstrated and compared with the traditional PLBS coating. The mixture-based PLBS coating shows good spectral performance, low surface roughness, and high LIDT. For an s -polarized 8 ns pulse laser at a wavelength of 1064 nm, a mixture-based PLBS coating design can improve LIDT by a factor of ∼ 2 with a slightly wider bandwidth. This tunable mixture-based PLBS coating design strategy provides support for the increasingly high output power of high-power laser systems. [ABSTRACT FROM AUTHOR]

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]

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 laser-induced damage threshold (LIDT) of HfO 2 /SiO 2 anti-reflection (AR) films for ultraviolet (UV) lasers was improved via low-temperature plasma-enhanced atomic layer deposition (PEALD). Focused on the chemical composition, optical absorption, surface scattering, and laser-resistance, the impact of precursor exposure time on PEALD SiO 2 film properties and growth temperature on PEALD SiO 2 and HfO 2 film properties were investigated respectively. When irradiated by UV laser, PEALD SiO 2 film exhibits a higher LIDT than the PEALD HfO 2 film, which is consistent with their less impurity content and lower absorption. A bilayer structure HfO 2 /SiO 2 AR film for 355 nm laser was designed and experimentally demonstrated via PEALD growth at a temperature of 150 °C. The prepared PEALD AR film shows a reflectance <0.2% at 355 nm as designed and better laser-damage resistance with a LIDT of 24.4 J/cm2 (355 nm, 7.8 ns) than the conventional e-beam deposition method. Image 1 • The HfO 2 /SiO 2 anti-reflection film for UV laser was presented via low-temperature PEALD. • The presented PEALD AR film shows better laser-damage resistance than conventional e-beam deposition method. • The impact of precursor exposure time on PEALD film properties were investigated. • The XPS measurement shows the impurity content of PEALD HfO 2 film is high, leading to a large absorption and low LIDT. [ABSTRACT FROM AUTHOR]

• Four hybrid materials (HfO 2 /Al 2 O 3 nanolaminate, HfO 2 /SiO 2 nanolaminate, HfO 2 -Al 2 O 3 mixture, and HfO 2 -SiO 2 mixture coatings) are investigated. • Hybrid materials show suppressed crystallization and reduced surface roughness, enabling tunable bandgaps and optical constants. • Hybrid-material-based mirror coatings are investigated and mixture-based mirror coatings have the highest LIDT. • The damage initiation mechanism of the mirror coating varies around 3 ps for laser pulses ranging from 0.5 to 8 ps.. Four hybrid materials (HfO 2 /Al 2 O 3 nanolaminate, HfO 2 /SiO 2 nanolaminate, HfO 2 –Al 2 O 3 mixture, and HfO 2 –SiO 2 mixture) and four hybrid-material-based mirror coatings are prepared via electron-beam evaporation. The refractive index (n), optical bandgaps, and microstructural properties of the hybrid materials are investigated and compared with those of pure materials. Experimental results show that the hybrid materials suppress crystallization, reduce surface roughness, and provide tunable bandgaps and optical constants. Among the four hybrid materials with similar n values, the HfO 2 –Al 2 O 3 mixture shows the largest bandgap. All the hybrid-material-based mirror coatings exhibit a higher laser-induced damage threshold (LIDT) at 8 picosecond (ps) than the conventional pure-material-based mirror coating. The HfO 2 –Al 2 O 3 mixture-based mirror coating with a relative high LIDT is used for further study of the pulse width dependence of the LIDT, and shows superior LIDT over the conventional mirror coating at 0.5 ps, 1 ps and 3 ps. Typical damage morphological features induced at different pulse widths show that the damage-initiation mechanism of the mirror coating changes around 3 ps. [ABSTRACT FROM AUTHOR]