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HfO(2) thin films were deposited by e-beam evaporation, and were post-treated with plasma under different flow rate ratios of argon to oxygen. By measuring the surface defect density, weak absorption, laser-induced damage threshold (LIDT) and damage morphology, the influence of the flow rate ratio of argon to oxygen on the laser-induced damage characters of HfO(2) thin films were analyzed. The experimental results show that plasma treatment is effective in reducing the surface defect density of thin films. Compared with the as-grown sample, the absorption reduction is obvious after plasma treatment when argon and oxygen flow rate ratio is 5:25, but the absorption increases gradually with the continued increase of argon and oxygen flow rate ratio. LIDT measurements in 1-on-1 mode demonstrate that plasma treatment is not effective in improving LIDT of the samples at 355 nm. Damage morphologies reveal that the LIDT is dominated by nanoscale absorbing defects in subsurface layers, which agrees well with our numerical simulation result based on a spherical absorber model.