23 November 2017 HfO2-SiO2 mixed film deposited by ion assisted deposition coevaporation
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Low absorption, low scattering and high-density HfO2 coatings lead to an important improvement of high power laser systems. In order to suppress the crystallization of HfO2 coatings fabricated with ion assisted deposition (IAD), we used double electron-beam (EB) coevaporation with ion beam assisting method to fabricate HfO2-SiO2 mixtures from two independent material sources. Crystallization following the different mixture ratios was investigated. Several prototypes were designed, featuring different HfO2-SiO2 ratios with similar physical thickness (500nm). The samples were deposited on fused silica and silicon substrates. X-ray diffraction patterns show that the degree of crystallization gradually fades away with increasing SiO2 contents and when SiO2 component reach 18%, the mixture film becomes almost amorphous. To decrease the high absorption originating from IAD method, thermal annealing in air at progressive temperatures was subsequently performed. It was found that post-annealing treatment at 600°C could eliminate the absorption at 1064nm. However, high temperature annealing would induce the crystallization of these initial amorphous coatings. In order to suppress the crystallization further to obtain amorphous structure even after 600°C annealing, the 25% SiO2 sample was fabricated and it successfully obtain low roughness and low absorption equivalent to the bare substrate. Finally, a 1064 nm HR coating using SiO2 and mixed film of 25% SiO2 concentration was prepared and annealed to prove its practical application in low loss and high LIDT optical elements.
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Xinshang Niu, Xinshang Niu, Hongfei Jiao, Hongfei Jiao, Ganghua Bao, Ganghua Bao, Jinlong Zhang, Jinlong Zhang, Xinbin Cheng, Xinbin Cheng, Zhanshan Wang, Zhanshan Wang, } "HfO2-SiO2 mixed film deposited by ion assisted deposition coevaporation", Proc. SPIE 10447, Laser-Induced Damage in Optical Materials 2017, 1044726 (23 November 2017); doi: 10.1117/12.2280438; https://doi.org/10.1117/12.2280438

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