Aluminum (Al)-based metal-dielectric composite coatings play a crucial role in the production of vacuum ultraviolet (VUV) optical components and laser systems. In the short-wavelength range of the VUV region, there is a high demand for practical Al-based coatings with high reflectivity, which imposes strict requirements on the preparation process. Key parameters of the preparation process, such as deposition rate, film thickness, and deposition temperature, significantly influence the growth and short-wavelength VUV optical properties of the coatings. In this study, we utilized electron-beam evaporation technology to prepare magnesium fluoride (MgF2) protected Al coatings for short-wavelength VUV reflection. We explored the impact of the aforementioned key process factors on the coatings’ properties and improved the reflectivity of the coatings in the short-wavelength VUV range, achieving reflectivity above 85% at the wavelength of 121.6 nm.
Meter-scale transmission mirror was one of the most important components for the giant solid-state laser device. Innovative method was adopted to realized multi-performance control by coupling different steps. Meter-scale transmission mirrors with high comprehensive performance were firstly coated. And the results were the best as reported so far.
HfO2 coatings are undoubtedly one of the most successful materials for high power laser applications. The ion beam assistance during the film growth is one of the most useful methods to obtain dense film along with improved optical and structural properties. As a consequence of the ever increasing application field of modern optical technologies, new demands for the optimization of deposition processes for high quality optical coatings with increased power handling capability, lower stress and optical uniformity are required for HfO2 film. In this paper, HfO2 films have been evaporated with ion assistance, provided by three different ion or plasma sources (APS, lion, RF). The influence of working gas flow (Ar and O2), ion energy and ion beam density on the HfO2 film properties was experimentally investigated. The film properties such as index of refraction, optical absorption and residual stress have been examined by spectrophotometry, laser calorimetry, and substrate curvature measurements. Microstructure have been studied by xray diffraction. Furthermore, a set of HfO2 monolayer were tested for LIDT at 1064 nm and 355nm for 10 ns pulses. The results suggest that the residual stress of HfO2 film is correlated with momentum transfer parameter, while both the ion energy and working gas flow maybe critical for the LIDT (absorption). The correlation between the microstructure and HfO2 film properties is discussed.
HfO2 thin films were evaporated with ion beam assistance to achieve dense, homogeneous, stoichiometric and low-stress films. The ion beam energy were related to the optical and structural properties of the film. The absorption coefficient and the refractive index were measured by spectrophotometric technique while the microstructure has been studied by means of x-ray diffraction and atomic force microscopy. The correlation between the structure, optical properties and laser damage threshold were analyzed. The results suggest the HfO2 structure and laser damage properties are closely related to the momentum transfer process during film deposition.
With the progress of high power laser system, the specifications of the large-aperture optics on the
low-spatial-frequency wavefront, mid-spatial-frequency wavefront, high-spatial-frequency wavefront
all meet stricter requirements. To the mid-spatial-frequency wavefront, it has been researched less than
others. The influence factors of the mid-spatial-frequency wavefront PSD1 error for large-aperture
mirrors are analyzed in this work. The results show that the influence factors of the
mid-spatial-frequency wavefront is different with the low-spatial-frequency wavefront. PV error
depends on the peak and vale of film surface,Grms error is affected by the big amplitude wave of film
surface, and PSD1 error is mainly caused by the small frequency wave of film surface. So it is the key
to controlling the PSD1 error for large-aperture mirrors that reducing small frequency wave of film
surface.
Damage tests were carried out to measure the laser resistance of Al2O3/TiO2 and Al2O3/HfO2
antireflection coatings at 1064nm grown by atomic layer deposition (ALD). The S-on-1 and
R-on-1 damage results are given. It's interesting to find that ALD coatings damage performance
seems closed to those grown by conventional e-beam evaporation process. For Al2O3/TiO2
coatings, the grown temperature will impact the damage resistance of thin films. Crystallization of
TiO2 layer at higher temperature could play an importance role as absorption defects that reduced
the LIDT of coatings. In addition, it is found that using inorganic compound instead of organic
compound as precursors for ALD process can effective prevent residual carbon in films and will
increase the LIDT of coatings.
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